MAX1645B [MAXIM]
Advanced Chemistry-Independent, Level 2 Battery Charger with Input Current Limiting; 先进的化学类型无关的Level 2电池充电器，带有输入限流
| 型号： | MAX1645B |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Advanced Chemistry-Independent, Level 2 Battery Charger with Input Current Limiting |
| 文件： | 总32页 (文件大小：354K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-2593; Rev 0; 10/02
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
General Description
Features
The MAX1645B is a high-efficiency battery charger
capable of charging batteries of any chemistry type. It
uses the Intel System Management Bus (SMBus) to
control voltage and current-charge outputs.
o Input Current Limiting
o 175s Charge Safety Timeout
o 128mA Wake-Up Charge
When charging lithium-ion (Li+) batteries, the MAX1645B
automatically transitions from regulating current to regu-
lating voltage. The MAX1645B can also limit line input
current so as not to exceed a predetermined current
drawn from the DC source. A 175s charge safety timer
prevents “runaway charging” should the MAX1645B stop
receiving charging voltage/current commands.
o Charges Any Chemistry Battery: Li+, NiCd,
NiMH, Lead Acid, etc.
o Intel SMBus 2-Wire Serial Interface
o Compliant with Level 2 Smart Battery Charger
Spec Rev 1.0
o +8V to +28V Input Voltage Range
o Up to 18.4V Battery Voltage
o 11-Bit Battery Voltage Setting
The MAX1645B employs a next-generation synchro-
nous buck control circuitry that lowers the minimum
input-to-output voltage drop by allowing the duty cycle
to exceed 99%. The MAX1645B can easily charge one
to four series Li+ cells.
o
0.8ꢀ ꢁutput Voltage Accuracy with Internal
Reference
Applications
o 3A (max) Battery Charge Current
o 6-Bit Charge-Current Setting
Notebook Computers
Point-of-Sale Terminals
Personal Digital Assistants
o 99.99ꢀ (max) Duty Cycle for Low-Dropout
ꢁperation
o Load/Source Switchover Drivers
o >97ꢀ Efficiency
Pin Configuration
Ordering Information
TOP VIEW
PART
TEMP RANGE
PIN-PACKAGE
MAX1645BEEI
-40°C to +125°C
28 QSOP
DCIN
LDO
CLS
REF
1
2
3
4
5
6
7
8
9
28 CVS
27 PDS
26 CSSP
25 CSSN
24 BST
23 DHI
CCS
CCI
MAX1645B
CCV
GND
BATT
22 LX
21 DLOV
20 DLO
19 PGND
18 CSIP
17 CSIN
16 PDL
15 INT
DAC 10
11
V
DD
Typical Operating Circuit appears at end of data sheet.
THM 12
SCL 13
SDA 14
SMBus is a trademark of Intel Corp.
QSꢁP
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
ABSꢁLUTE MAXIMUM RATINGS
DCIN, CVS, CSSP, CSSN, LX to GND....................-0.3V to +30V
CSSP to CSSN, CSIP to CSIN ...............................-0.3V to +0.3V
V
, SCL, SDA, INT, DLOV to GND.........................-0.3V to +6V
DD
THM to GND...............................................-0.3V to (V
+ 0.3V)
DD
PDS, PDL to GND ...................................-0.3V to (V
BST to LX..................................................................-0.3V to +6V
DHI to LX...................................................-0.3V to (V + 0.3V)
+ 0.3V)
PGND to GND .......................................................-0.3V to +0.3V
LDO Continuous Current.....................................................50mA
CSSP
Continuous Power Dissipation (T = +70°C)
BST
A
CSIP, CSIN, BATT to GND .....................................-0.3V to +22V
28-Pin QSOP (derate 10.8mW/°C above +70°C).........860mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range.............................-60°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
LDO to GND.....................-0.3V to (lower of 6V or V
+ 0.3V)
+ 0.3V)
+ 0.3V)
DCIN
DLO to GND ...........................................-0.3V to (V
DLOV
REF, DAC, CCV, CCI, CCS, CLS to GND.....-0.3V to (V
LDO
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V
= +3.3V, V
= +16.8V, V
= +18V, T = 0°C to +85°C, unless otherwise noted. Typical values are at
A
DCIN
DD
BATT
T
A
= +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL SPECIFICATIONS
DCIN Typical Operating Range
DCIN Supply Current
V
8
28
6
V
DCIN
I
8V < V
< 28V
1.7
0.7
mA
DCIN
DCIN
DCIN
DCIN Supply Current Charging
Inhibited
8V < V
< 28V
2
mA
V
DCIN rising
DCIN falling
7.5
7.4
5.4
7.85
When AC_PRESENT
switches
DCIN Undervoltage Threshold
7
LDO Output Voltage
V
8V < V
8V < V
< 28V, 0 < I < 15mA
LDO
5.15
2.80
5.65
5.65
2.8
V
V
LDO
DCIN
DCIN
V
V
Input Voltage Range
< 28V (Note 1)
V
DD
DD
rising
falling
2.55
2.5
DD
DD
When the SMB
responds to commands
Undervoltage Threshold
V
V
2.1
0 < V
< 6V, V
= 5V, V
= 5V,
SCL
DCIN
= 5V
DD
V
Quiescent Current
I
80
150
µA
DD
DD
V
SDA
REF Output Voltage
V
0 < I
< 200µA
4.066
2.4
4.096
4.126
2.8
V
V
REF
REF
BATT Undervoltage Threshold
When I
drops to 128mA (Note 2)
CHARGE
PDS Charging Source Switch
Turn-Off Threshold
V
V
V
V
referred to V
referred to V
= 0
, V
falling
50
100
8
100
200
10
150
300
mV
mV
V
PDS-OFF
CVS
CVS
PDS
BATT CVS
PDS Charging Source Switch
Threshold Hysteresis
PDS-HYS
BATT
PDS Output Low Voltage, PDS
Below CSSP
I
12
PDS Turn-On Current
PDS Turn-Off Current
PDS = CSSP
100
10
150
50
300
µA
V
= V
- 2V, V = 16V
DCIN
mA
PDS
CSSP
PDL Load Switch Turn-Off
Threshold
V
V
referred to V , V rising
BATT CVS
-150
-100
-50
mV
PDL-OFF
CVS
2
_______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
= +3.3V, V
= +16.8V, V
= +18V, T = 0°C to +85°C, unless otherwise noted. Typical values are at
A
DCIN
DD
BATT
T
A
= +25°C.)
PARAMETER
SYMBOL
CONDITIONS
referred to V
MIN
TYP
MAX
UNITS
PDL Load Switch Threshold
Hysteresis
V
V
V
100
200
300
mV
PDL-HYS
CVS
BATT
PDL Turn-Off Current
PDL Turn-On Resistance
CVS Input Bias Current
- V
PDL
= 1V
6
12
100
6
mA
kΩ
µA
CSSN
PDL to GND
= 28V
50
150
20
V
CVS
ChargingVoltage() = 0x41A0
ChargingVoltage() = 0x3130
ChargingVoltage() = 0x20D0
ChargingVoltage() = 0x1060
16.666
16.8
16.934
12.492 12.592 12.692
BATT Full-Charge Voltage
V0
I0
V
8.333
4.150
8.4
8.467
4.234
4.192
ChargingCurrent() =
139.9
3.08
150.4
6.4
160.9
9.72
0x0BC0
BATT Charge Current-Sense
Voltage
V
V
- V
mV
mV
CSIP
CSIN
ChargingCurrent() =
0x0080
V
V
= 4.096V
= 2.048V
188.6
91.3
204.8
102.4
221.0
113.5
CLS
CLS
DCIN Source Current-Limit
Sense Voltage
- V
CSSP
CSSN
BATT Undervoltage Charge
Current-Sense Voltage
V
V
- V
- V
V
= 1V
3.08
250
0
6.4
9.72
350
20
mV
mV
V
CSIP
CSIP
CSIN
BATT
Inductor Peak Current Limit
300
CSIN
BATT/CSIP/CSIN Input Voltage
Range
Total of I
, I
, and I
, and I
;
CSIN
BATT CSIP
Total BATT Input Bias Current
Total BATT Quiescent Current
Total BATT Standby Current
-700
-100
-5
+700
+100
+5
µA
µA
µA
V
= 0 to 20V
BATT
Total of I
, I
;
CSIN
BATT CSIP
V
= 0 to 20V, charge inhibited
BATT
Total of I
, I
, and I
;
CSIN
BATT CSIP
V
V
V
V
= 0 to 20V, V
= 0
BATT
DCIN
CSSP Input Bias Current
CSSN Input Bias Current
CSSP/CSSN Quiescent Current
= V
= V
CSSN
= 0 to 28V
= 0 to 28V
-100
-100
-1
540
35
+1000
+100
+1
µA
µA
µA
CSSP
CSSP
CSSP
DCIN
= C
= V
DCIN
CSSN
CSSN
= V
= 28V, V
= 0
DCIN
Battery Voltage-Error Amp DC
Gain
From BATT to CCV
= V /2 to V
REF
200
-1
500
V/V
µA
CLS Input Bias Current
V
+0.05
0.222
+1
CLS
REF
Battery Voltage-Error Amp
Transconductance
From BATT to CCV, ChargingVoltage() =
0x41A0, V = 16.8V
0.111
0.444
µA/mV
BATT
Battery Current-Error Amp
Transconductance
From CSIP/CSIN to CCI, ChargingCurrent()
= 0x0BC0, V - V = 150.4mV
0.5
1
2.0
µA/mV
CSIP
CSIN
Input Current-Error Amp
Transconductance
From CSSP/CSSN to CCS, V
= 2.048V,
CLS
0.5
1
2.0
µA/mV
mV
V
- V
CSSN
= 102.4mV
CSSP
CCV/CCI/CCS Clamp Voltage
V
= V
= V = 0.25V to 2V (Note 3)
CCS
150
300
600
CCV
CCI
_______________________________________________________________________________________
3
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
= +3.3V, V
= +16.8V, V
= +18V, T = 0°C to +85°C, unless otherwise noted. Typical values are at
A
DCIN
DD
BATT
T
A
= +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DC-TO-DC CONVERTER SPECIFICATIONS
Minimum Off-Time
t
1.0
5
1.25
10
1.5
15
µs
ms
%
OFF
Maximum On-Time
t
ON
Maximum Duty Cycle
LX Input Bias Current
LX Input Quiescent Current
BST Supply Current
DLOV Supply Current
DHI Output Resistance
DLO Output Resistance
99
99.99
200
V
V
= 28V, V
= V = 20V
500
1
µA
µA
µA
µA
Ω
DCIN
DCIN
BATT
LX
= 0, V
= V = 20V
LX
BATT
DHI high
= V
6
5
6
6
15
10
14
14
V
, DLO low
LDO
DLOV
DHI high or low, V
- V = 4.5V
LX
BST
DLO high or low, V
= 4.5V
Ω
DLOV
THERMISTOR COMPARATOR SPECIFICATIONS
V
= 4% of V
to 96% of V , V
=
THM
DD
DD DD
THM Input Bias Current
-1
+1
µA
2.8V to 5.65V
Thermistor Overrange Threshold
Thermistor Cold Threshold
Thermistor Hot Threshold
V
V
V
= 2.8V to 5.65V, V
= 2.8V to 5.65V, V
= 2.8V to 5.65V, V
falling
falling
falling
89.5
74
91
92.5
77
% of V
DD
DD
DD
DD
THM
THM
THM
75.5
23.5
% of V
% of V
DD
DD
22
25
Thermistor Underrange
Threshold
V
= 2.8V to 5.65V, V
falling
6
7.5
1
9
% of V
DD
DD
THM
Thermistor Comparator
Threshold Hysteresis
All four comparators, V
= 2.8V to 5.65V
% of V
DD
DD
SMB INTERFACE LEVEL SPECIFICATIONS (V
SDA/SCL Input Low Voltage
= 2.8V to 5.65V)
DD
0.6
+1
V
SDA/SCL Input High Voltage
1.4
V
SDA/SCL Input Hysteresis
220
25
mV
µA
mA
µA
mV
SDA/SCL Input Bias Current
-1
6
SDA Output Low Sink Current
INT Output High Leakage
V
V
= 0.4V
SDA
= 5.65V
1
I NT
INT Output Low Voltage
I
= 1mA
200
I NT
SMB INTERFACE TIMING SPECIFICATIONS (V
= 2.8V to 5.65V, Figures 4 and 5)
DD
SCL High Period
SCL Low Period
t
4
µs
µs
HIGH
t
4.7
LOW
Start Condition Setup Time
from SCL
t
4.7
4
µs
µs
SU:STA
Start Condition Hold Time
from SCL
t
t
HD:STA
SDA Setup Time from SCL
SDA Hold Time from SCL
250
0
ns
ns
SU:DAT
HD:DAT
t
4
_______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
= +3.3V, V
= +16.8V, V
= +18V, T = 0°C to +85°C, unless otherwise noted. Typical values are at
A
DCIN
DD
BATT
T
A
= +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SDA Output Data Valid from SCL
t
1
µs
DV
Maximum Charge Period Without
a ChargingVoltage() or
t
140
175
210
s
WDT
Charging Current() Loaded
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V = +3.3V, V
DD
= +16.8V, V
= +18V, T = -40°C to +85°C, unless otherwise noted. Guaranteed by design.)
BATT
DCIN A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL SPECIFICATIONS
DCIN Typical Operating Range
DCIN Supply Current
V
8
28
6
V
DCIN
I
8V < V
8V < V
< 28V
mA
DCIN
DCIN
DCIN
DCIN Supply Current Charging
Inhibited
< 28V
2
mA
V
DCIN rising
DCIN falling
7.85
When AC_PRESENT
switches
DCIN Undervoltage Threshold
7
LDO Output Voltage
V
8V < V
8V < V
< 28V, 0 < I < 15mA
LDO
5.15
2.80
5.65
5.65
2.8
V
V
LDO
DCIN
DCIN
V
V
Input Voltage Range
< 28V (Note 1)
V
DD
DD
rising
falling
DD
DD
When the SMB
responds to commands
Undervoltage Threshold
V
V
2.1
0 < V
< 6V, V
= 5V, V
= 5V,
SCL
DCIN
= 5V
DD
V
Quiescent Current
I
150
µA
DD
DD
V
SDA
REF Output Voltage
V
0 < I
< 200µA
4.035
2.4
4.157
2.8
V
V
REF
REF
BATT Undervoltage Threshold
When I
drops to 128mA (Note 2)
CHARGE
PDS Charging Source Switch
Turn-Off Threshold
V
V
V
V
referred to V
referred to V
= 0
, V
falling
50
100
8
150
300
mV
mV
V
PDS-OFF
CVS
CVS
PDS
BATT CVS
PDS Charging Source Switch
Threshold Hysteresis
PDS-HYS
BATT
PDS Output Low Voltage, PDS
Below CSSP
I
12
PDS Turn-On Current
PDS Turn-Off Current
PDS = CSSP
100
10
300
µA
V
= V
- 2V, V = 16V
DCIN
mA
PDS
CSSP
PDL Load Switch Turn-Off
Threshold
V
V
V
referred to V
referred to V
, V
rising
-150
-50
mV
PDL-OFF
PDL-HYS
CVS
BATT CVS
PDL Load Switch Threshold
Hysteresis
V
V
100
6
300
mV
mA
CVS
BATT
PDL Turn-Off Current
- V
PDL
= 1V
CSSN
_______________________________________________________________________________________
5
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V = +3.3V, V
DD
= +16.8V, V = +18V, T = -40°C to +85°C, unless otherwise noted. Guaranteed by design.)
DCIN A
BATT
PARAMETER
PDL Turn-On Resistance
CVS Input Bias Current
SYMBOL
CONDITIONS
MIN
TYP
MAX
150
20
UNITS
kΩ
PDL to GND
50
V
= 28V
µA
CVS
ERROR AMPLIFIER SPECIFICATIONS
ChargingVoltage() = 0x41A0
ChargingVoltage() = 0x3130
ChargingVoltage() = 0x20D0
ChargingVoltage() = 0x1060
16.532
12.391
8.266
17.068
12.793
8.534
BATT Full-Charge Voltage
V0
I0
V
4.124
4.260
ChargingCurrent() =
130.4
0.76
170.4
12.04
0x0BC0
BATT Charge Current-Sense
Voltage
V
V
- V
mV
mV
CSIP
CSIN
ChargingCurrent() =
0x0080
V
V
= 4.096V
= 2.048V
174.3
82.2
235.3
120.2
CLS
CLS
DCIN Source Current-Limit
Sense Voltage
- V
CSSP
CSSN
BATT Undervoltage Charge
Current-Sense Voltage
V
V
= 1V, V
- V
CSIN
1
250
0
10
350
20
mV
mV
V
BATT
CSIP
CSIP
Inductor Peak Current Limit
- V
CSIN
BATT/CSIP/CSIN Input Voltage
Range
Total of I
, I
, and I
, and I
;
CSIN
BATT CSIP
Total BATT Input Bias Current
Total BATT Quiescent Current
Total BATT Standby Current
-700
-100
-5
+700
+100
+5
µA
µA
µA
V
= 0 to 20V
BATT
Total of I
, I
;
CSIN
BATT CSIP
V
= 0 to 20V, charge inhibited
BATT
Total of I
, I
, and I
;
CSIN
BATT CSIP
V
V
V
V
= 0 to 20V, V
= 0
BATT
DCIN
CSSP/Input Bias Current
CSSN Input Bias Current
CSSP/CSSN Quiescent Current
= V
= V
CSSN
= 0 to 28V
= 0 to 28V
-100
-100
-1
+1000
+100
+1
µA
mA
µA
CSSP
CSSP
CSSP
DCIN
= C
= V
DCIN
CSSN
CSSN
= V
= 28V, V
= 0
DCIN
Battery Voltage-Error Amp DC
Gain
From BATT to CCV
= V /2 to V
REF
200
-1
V/V
µA
CLS Input Bias Current
V
+1
CLS
REF
Battery Voltage-Error Amp
Transconductance
From BATT to CCV, ChargingVoltage() =
0x41A0, V = 16.8V
0.111
0.444
µA/mV
BATT
Battery Current-Error Amp
Transconductance
From CSIP/CSIN to CCI, ChargingCurrent()
= 0x0BC0, V - V = 150.4mV
0.5
2.0
µA/mV
CSIP
CSIN
Input Current-Error Amp
Transconductance
From CSSP/CSSN to CCS, V
= 2.048V,
CLS
0.5
2.0
µA/mV
mV
V
- V
CSSN
= 102.4mV
CSSP
CCV/CCI/CCS Clamp Voltage
V
= V
= V = 0.25V to 2V (Note 3)
CCS
150
600
CCV
CCI
6
_______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V = +3.3V, V
DD
= +16.8V, V = +18V, T = -40°C to +85°C, unless otherwise noted. Guaranteed by design.)
DCIN A
BATT
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DC-TO-DC CONVERTER SPECIFICATIONS
Minimum Off-Time
t
1.0
5
1.5
15
µs
ms
%
OFF
Maximum On-Time
t
ON
Maximum Duty Cycle
LX Input Bias Current
LX Input Quiescent Current
BST Supply Current
DLOV Supply Current
DHI Output Resistance
DLO Output Resistance
99
V
= 28V, V
= V = 20V
500
1
µA
µA
µA
µA
Ω
DCIN
DCIN
BATT
LX
V
= 0, V
= V = 20V
BATT LX
DHI high
= V
15
10
14
14
V
, DLO low
LDO
DLOV
DHI high or low, V
- V = 4.5V
LX
BST
DLO high or low, V
= 4.5V
Ω
DLOV
THERMISTOR COMPARATOR SPECIFICATIONS
V
V
= 4% of V
= 2.8V to 5.65V
to 96% of V
,
DD
THM
DD
THM Input Bias Current
-1
+1
µA
DD
Thermistor Overrange Threshold
Thermistor Cold Threshold
Thermistor Hot Threshold
V
V
V
= 2.8V to 5.65V, V
= 2.8V to 5.65V, V
= 2.8V to 5.65V, V
falling
falling
falling
89.5
74
92.5
77
% of V
DD
DD
DD
DD
THM
THM
THM
% of V
DD
22
25
% of V
DD
Thermistor Underrange
Threshold
V
= 2.8V to 5.65V, V
falling
6
9
% of V
DD
DD
THM
SMB INTERFACE LEVEL SPECIFICATIONS (V
SDA/SCL Input Low Voltage
= 2.8V to 5.65V)
DD
0.6
+1
V
SDA/SCL Input High Voltage
1.4
-1
6
V
SDA/SCL Input Bias Current
µA
mA
µA
mV
SDA Output Low Sink Current
V
V
= 0.4V
SDA
INT Output High Leakage
= 5.65V
1
I NT
INT Output Low Voltage
I
= 1mA
200
I NT
SMB INTERFACE TIMING SPECIFICATIONS (V
= 2.8V to 5.65V, Figures 4 and 5)
DD
SCL High Period
SCL Low Period
t
4
µs
µs
HIGH
t
4.7
LOW
Start Condition Setup Time
from SCL
t
4.7
4
µs
µs
SU:STA
Start Condition Hold Time
from SCL
t
t
HD:STA
SDA Setup Time from SCL
SDA Hold Time from SCL
250
0
ns
ns
SU:DAT
HD:DAT
t
_______________________________________________________________________________________
7
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V = +3.3V, V
DD
= +16.8V, V = +18V, T = -40°C to +85°C, unless otherwise noted. Guaranteed by design.)
DCIN A
BATT
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SDA Output Data Valid from SCL
t
1
µs
DV
Maximum Charge Period Without
a ChargingVoltage() or
t
140
210
s
WDT
Charging Current() Loaded
Note 1: Guaranteed by meeting the SMB timing specs.
Note 2: The charger reverts to a trickle-charge mode of I
= 128mA below this threshold.
CHARGE
Note 3: Voltage difference between CCV and CCI or CCS when one of these three pins is held low and the others try to pull high.
Typical Operating Characteristics
(Circuit of Figure 1, V
= 20V, T = +25°C, unless otherwise noted.)
A
DCIN
LOAD-TRANSIENT RESPONSE
(STEP-IN LOAD CURRENT)
BATTERY REMOVAL AND REINSERTION
LDO LINE REGULATION
TRANSIENT RESPONSE
MAX1645B toc02
MAX1645B toc01
5.60
5.55
5.50
5.45
5.40
5.35
5.30
5.25
5.20
I
= 0
LOAD
15.5V
15.0V
16V
15V
1A
CCS
CCS
CCI
2.75V
2.25V
1.75V
CCV
CCV
0
CCI
1.25V
CCI
CCI
0.75V
0.25V
CCI
CCI
CCV
CCS
0.75V
BATTERY REMOVED
BATTERY INSERTED
400µs/div
5
10
15
20
(V)
25
30
2ms/div
ChargingCurrent() = 3.0A
0 TO 2A LOAD STEP, V
SOURCE
V
DCIN
ChargingVoltage() = 16000mV
ChargingCurrent() = 1000mA
= 20V
BATT
I
LIMIT = 2.5A
REFERENCE VOLTAGE
vs. TEMPERATURE
REFERENCE VOLTAGE LOAD REGULATION
LDO LOAD REGULATION
4.100
4.098
4.096
4.094
4.092
4.090
5.60
5.55
5.50
5.45
5.40
5.35
5.30
5.25
5.20
4.110
4.105
4.100
4.095
4.090
4.085
4.080
0
50
100
150
200
250
300
0
2
4
6
8
10 12 14 16 18 20
-40 -20
0
20
40
60
80 100
LOAD CURRENT (µA)
LOAD CURRENT (mA)
TEMPERATURE (°C)
8
_______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
= 20V, T = +25°C, unless otherwise noted.)
A
DCIN
EFFICIENCY vs. BATTERY CURRENT
(VOLTAGE-CONTROL LOOP)
EFFICIENCY vs. BATTERY CURRENT
(CURRENT-CONTROL LOOP)
OUTPUT VI CHARACTERISTICS
100
95
90
85
80
75
70
65
60
55
50
100
95
90
85
80
75
70
65
60
55
50
0.001
0.01
0.1
A
B
A
B
1.0
ChargingVoltage() = 16800mV
ChargingCurrent() = 3008mA
A: V
B: V
= 20V, ChargingVoltage() = 16.8V
= 16V, ChargingVoltage() = 8.4V
A: V
B: V
= 20V, V
= 16V, V
= 16.8V
= 8.4V
DCIN
DCIN
DCIN
DCIN
BATT
BATT
10
0
500 1000 1500 2000 2500 3000 3500
LOAD CURRENT (mA)
0
500 1000 1500 2000 2500 3000
BATTERY CURRENT (mA)
0
500 1000 1500 2000 2500 3000
ChargingCurrent() (CODE)
BATT VOLTAGE ERROR
vs. ChargingVoltage() CODE
0.3
CURRENT-SETTING ERROR
vs. ChargingCurrent() CODE
5
4
0.2
0.1
0
3
2
1
0
-1
-2
-3
-4
-0.1
-0.2
I
= 0
V
= 12.6V
BATT
BATT
MEASURED AT AVAILABLE CODES
4000 8000 12,000 16,000 20,000
ChargingVoltage() (CODE)
MEASURED AT AVAILABLE CODES
-0.3
-5
0
0
500 1000 1500 2000 2500 3000
ChargingCurrent() (CODE)
SOURCE/BATT CURRENT vs. LOAD CURRENT
WITH SOURCE CURRENT LIMIT
SOURCE/BATT CURRENT vs. V
WITH SOURCE CURRENT LIMIT
BATT
3.5
3.5
3.0
2.5
2.0
3.0
2.5
2.0
1.5
1.0
0.5
0
I
I
IN
IN
1.5
I
V
R
V
= 2V
= 2A
= 2V
CLS
CSS
LOAD
= 40mΩ
= 16.8V
V
R
CLS
CSS
1.0
0.5
0
I
I
BATT
BATT
= 40mΩ
BATT
SOURCE CURRENT LIMIT = 2.5A
ChargingCurrent() = 3008mA
ChargingVoltage() = 18432mV
ChargingVoltage() = 18432mV
ChargingCurrent() = 3008mA
SOURCE CURRENT LIMIT = 2.5A
0
0.5
1.0
1.5
2.0
2.5
0
2
4
6
8
10 12 14 16 18 20
(V)
LOAD CURRENT (A)
V
BATT
_______________________________________________________________________________________
9
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Pin Description
PIN
1
NAME
DCIN
LDO
CLS
FUNCTION
DC Supply Voltage Input
2
5.4V Linear-Regulator Voltage Output. Bypass with a 1µF capacitor to GND.
Source Current-Limit Input
3
4
REF
4.096V Reference Voltage Output
5
CCS
CCI
Charging Source Compensation Capacitor Connection. Connect a 0.01µF capacitor from CCS to GND.
Battery Current-Loop Compensation Capacitor Connection. Connect a 0.01µF capacitor from CCI to GND.
6
Battery Voltage-Loop Compensation Capacitor Connection. Connect a 10kΩ resistor in series with a 0.01µF
capacitor to GND.
7
CCV
8
GND
BATT
DAC
Ground
9
Battery Voltage Output
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
DAC Voltage Output
V
Logic Circuitry Supply Voltage Input (2.8V to 5.65V)
Thermistor Voltage Input
DD
THM
SCL
SDA
INT
SMB Clock Input
SMB Data Input/Output. Open-drain output. Needs external pullup.
Interrupt Output. Open-drain output. Needs external pullup.
PMOS Load Switch Driver Output
Battery Current-Sense Negative Input
Battery Current-Sense Positive Input
PDL
CSIN
CSIP
PGND Power Ground
DLO
DLOV
LX
Low-Side NMOS Driver Output
Low-Side NMOS Driver Supply Voltage. Bypass with 0.1µF capacitor to GND.
Inductor Voltage Sense Input
DHI
High-Side NMOS Driver Output
BST
High-Side Driver Bootstrap Voltage Input. Bypass with 0.1µF capacitor to LX.
Charging Source Current-Sense Negative Input
Charging Source Current-Sense Positive Input
Charging Source PMOS Switch Driver Output
Charging Source Voltage Input
CSSN
CSSP
PDS
CVS
10 ______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Input Current Limiting
Detailed Description
The MAX1645B limits the current drawn by the charger
The MAX1645B consists of current-sense amplifiers, an
when the load current becomes high. The device limits
SMBus interface, transconductance amplifiers, reference
the charging current so the AC adapter voltage is not
circuitry, and a DC-DC converter (Figure 2). The DC-DC
loaded down. An internal amplifier, CSS, compares the
converter generates the control signals for the external
voltage between CSSP and CSSN to the voltage at
MOSFETs to maintain the voltage and the current set by
CLS/20. V
and GND.
is set by a resistor-divider between REF
CLS
the SMBus interface. The MAX1645B features a voltage-
regulation loop and two current-regulation loops. The
loops operate independently of each other. The voltage-
regulation loop monitors BATT to ensure that its voltage
never exceeds the voltage set point (V0). The battery cur-
rent-regulation loop monitors current delivered to BATT to
ensure that it never exceeds the current-limit set point
(I0). The battery current-regulation loop is in control as
long as BATT voltage is below V0. When BATT voltage
reaches V0, the current loop no longer regulates. A third
loop reduces the battery-charging current when the sum
of the system (the main load) and the battery charger
input current exceeds the charging source current limit.
The input source current is the sum of the device cur-
rent, the charge input current, and the load current. The
device current is minimal (6mA max) in comparison to
the charge and load currents. The charger input cur-
rent is generated by the DC-DC converter; therefore, the
actual source current required is determined as follows:
I
= I
+ [(I ✕ V
CHARGE BATT)
/ (V ✕ η)]
IN
SOURCE
LOAD
where η is the efficiency of the DC-DC converter (typi-
cally 85% to 95%).
V
CLS
determines the threshold voltage of the CSS com-
parator. R3 and R4 (Figure 1) set the voltage at CLS.
Sense resistor R1 sets the maximum allowable source
current. Calculate the maximum current as follows:
Setting Output Voltage
The MAX1645B voltage DAC has a 16mV LSB and an
18.432V full scale. The SMBus specification allows for a
16-bit ChargingVoltage() command that translates to a
1mV LSB and a 65.535V full-scale voltage; therefore,
the ChargingVoltage() value corresponds to the output
voltage in millivolts. The MAX1645B ignores the first 4
LSBs and uses the next 11 LSBs to control the voltage
DAC. All codes greater than or equal to 0x4800
(18432mV) result in a voltage overrange, limiting the
charger voltage to 18.432V. All codes below 0x0400
(1024mV) terminate charging.
I
= V
/ (20 ✕ R )
MAX
CLS
1
(Limit V
- V
to between 102.4mV and
CSSN
CSSP
204.8mV.)
The configuration in Figure 1 provides an input current
limit of:
I
= (2.048V / 20) / 0.04Ω = 2.56A
MAX
LDO Regulator
Setting the Charge Current
The MAX1645B charge-current DAC has a 3.2mV to
150.4mV range. The SMBus specification allows for a
16-bit ChargingCurrent() command that translates to a
0.05mV LSB and a 3.376V full-scale current-sense volt-
age. The MAX1645B drops the first 6 LSBs and uses
the remaining 6 MSBs to control the charge-current
DAC. All codes above 0x0BC0 result in an overrange
condition, limiting the charge current-sense voltage to
150.4mV. All codes below 0x0080 turn off the charging
An integrated LDO regulator provides a +5.4V supply
derived from DCIN, which can deliver up to 15mA of
current. The LDO sets the gate-drive level of the NMOS
switches in the DC-DC converter. The drivers are actu-
ally powered by DLOV and BST, which must be con-
nected to LDO through a lowpass filter and a diode as
shown in Figure 1. Also see the MOSFET Drivers sec-
tion. The LDO also supplies the 4.096V reference and
most of the control circuitry. Bypass LDO with a 1µF
capacitor.
current. Therefore, the charging current (I
determined by:
) is
CHARGE
V
Supply
DD
This input provides power to the SMBus interface and
the thermistor comparators. Typically connect V to
I
= V
/ R
CHARGE
DACI CSI
DD
where V
is the current-sense voltage set by
DACI
LDO or, to keep the SMBus interface of the MAX1645B
active while the supply to DCIN is removed, connect an
ChargingCurrent(), and R
is the battery current-
CSI
sense resistor (R2 in Figure 1). When using a 50mΩ
current-sense resistor, the ChargingCurrent() value cor-
responds directly to the charging current in milliamps
(0x0400 = 1024mA = 52.2mV/50mΩ).
external supply to V
.
DD
______________________________________________________________________________________ 11
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
ADAPTER IN
R13
D4
P1
FDS6675
1kΩ
1N4148
D1
1N5821
PDS
CVS
R14
DCIN
4.7Ω
C23
0.1µF
CSSP
C5
C2
22µF
C1
22µF
1µF
C20, 1µF
C19, 1µF
R1
0.04Ω
MAX1645B
REF
CSSN
LDO
R15
4.7Ω
R3
100kΩ
C7
1µF
LOAD
C6
1µF
CLS
R12
33Ω
D3
CMPSH3
R4
100kΩ
BST
GND
DLOV
DAC
CCV
C16
0.22µF
C8
0.1µF
R17
10kΩ
C14
0.1µF
R5
10kΩ
DHI
LX
N1
FDS6680
CCI
C10
1nF
C9
0.01µF
R18
10kΩ
CCS
DLO
C11
1nF
L1
22µH
N2
FDS6612A
D2
1N5821
PGND
R11
1Ω
CSIP
C18
0.1µF
R2
0.05Ω
C24
0.1µF
R16
1Ω
CSIN
PDL
P2
FDS6675
C3
22µF
C4
22µF
BATT
R7
BATTERY
HOST
R6
10kΩ
10kΩ
THM
C13
1.5nF
V
DD
C12
1µF
R8
R10
10kΩ
10kΩ
R9
10kΩ
SCL
SDA
INT
Figure 1. Typical Application Circuit
12 ______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
BST
MAX1645B
DHI
LX
CSSP
CSSN
CLS
DHI
CSS
GMS
DC-DC
LVC
DLOV
DLO
DLO
CSIP
CSIN
CSI
PGND
GMI
BATT
CCS
CCI
CCV
GMV
CVS
BATT
PDL
PDS
PDS
PDL
DCIN
LDO
V
DD
VL
SCL
SDA
INT
DACI
SMB
REF
REF
DACV
GND
DAC
TEMP
THM
Figure 2. Functional Diagram
______________________________________________________________________________________ 13
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
The MAX1645B uses the SMBus read-word and write-
word protocols to communicate with the battery being
charged, as well as with any host system that monitors
the battery-to-charger communications as a Level 2
SMBus charger. The MAX1645B is an SMBus slave
device and does not initiate communication on the bus.
It receives commands and responds to queries for sta-
tus information. Figure 3 shows examples of the SMBus
write-word and read-word protocols, and Figures 4 and
5 show the SMBus serial-interface timing.
Operating Conditions
The MAX1645B changes its operation depending on
the voltages at DCIN, BATT, V
and THM. Several
DD,
important operating states follow:
• AC Present. When DCIN is >7.5V, the battery is con-
sidered to be in an AC present state. In this condi-
tion, both the LDO and REF function properly and
battery charging is allowed. When AC is present, the
AC_PRESENT bit (bit 15) in the ChargerStatus() reg-
ister is set to 1.
Each communication with this part begins with the
MASTER issuing a START condition that is defined as a
falling edge on SDA with SCL high and ends with a
STOP condition defined as a rising edge on SDA with
SCL high. Between the START and STOP conditions,
the device address, the command byte, and the data
bytes are sent. The MAX1645B’s device address is
0x12 and supports the charger commands as
described in Tables 1–6.
• Power Fail. When DCIN is <BATT + 0.3V, the part is
in the power-fail state, since the charger does not
have enough input voltage to charge the battery. In
power fail, the PDS input PMOS switch is turned off
and the POWER_FAIL bit (bit 13) in the
ChargerStatus() register is set to 1.
• Battery Present. When THM is <91% of V , the
DD
battery is considered to be present. The MAX1645B
uses the THM pin to detect when a battery is con-
nected to the charger. When the battery is present,
the BATTERY_PRESENT bit (bit 14) in the
ChargerStatus() register is set to 1 and charging can
proceed. When the battery is not present, all of the
registers are reset. With no battery present, the
charger performs a “float” charge to minimize con-
tact arcing on battery connection. The “float” charge
still tries to regulate the BATT pin voltage at 18.32V
with 128mA of current compliance.
Battery Charger Commands
ChargerSpecInfo()
The ChargerSpecInfo() command uses the read-word
protocol (Figure 3b). The command code for
ChargerSpecInfo() is 0x11 (0b00010001). Table 1 lists
the functions of the data bits (D0–D15). Bit 0 refers to the
D0 bit in the read-word protocol. The MAX1645B com-
plies with Level 2 Smart Battery Charger Specification
Revision 1.0; therefore, the ChargerSpecInfo() command
returns 0x09.
• Battery Undervoltage. When BATT <2.5V, the bat-
tery is in an undervoltage state. This causes the
charger to reduce its current compliance to 128mA.
The content of the ChargingCurrent() register is unaf-
fected and, when the BATT voltage exceeds 2.7V,
normal charging resumes. ChargingVoltage() is unaf-
fected and can be set as low as 1.024V.
ChargerMode()
The ChargerMode() command uses the write-word
protocol (Figure 3a). The command code for
ChargerMode() is 0x12 (0b00010010). Table 2 lists the
functions of the data bits (D0–D15). Bit 0 refers to the
D0 bit in the write-word protocol.
• V
Undervoltage. When V
<2.5V, the V
sup-
DD
DD
DD
To charge a battery that has a thermistor impedance in
the HOT range (i.e., THERMISTOR_HOT = 1 and
THERMISTOR_UR = 0), the host must use the
ChargerMode() command to clear HOT_STOP after the
battery is inserted. The HOT_STOP bit returns to its
default power-up condition (1) whenever the battery is
removed.
ply is in an undervoltage state, and the SMBus inter-
face does not respond to commands. Coming out of
the undervoltage condition, the part is in its Power-
On Reset state. No charging occurs when V
under voltage.
is
DD
SMBus Interface
The MAX1645B receives control inputs from the SMBus
interface. The serial interface complies with the SMBus
specification (refer to the System Management Bus
Specification from Intel Corporation). Charger function-
ality complies with the Intel/Duracell Smart Charger
Specification for a Level 2 charger.
ChargerStatus()
The ChargerStatus() command uses the read-word
protocol (Figure 3b). The command code for
ChargerStatus() is 0x13 (0b00010011). Table 3
describes the functions of the data bits (D0–D15). Bit 0
refers to the D0 bit in the read-word protocol.
14 ______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
The ChargerStatus() command returns information
about thermistor impedance and the MAX1645B’s inter-
nal state. The latched bits, THERMISTOR_HOT and
ALARM_INHIBITED, are cleared whenever BATTERY_
PRESENT = 0 or ChargerMode() is written with
POR_RESET = 1. The ALARM_INHIBITED status bit can
also be cleared by writing a new charging current OR
charging voltage.
a) Write-Word Format
LOW
DATA
BYTE
HIGH
DATA
BYTE
SLAVE
ADDRESS
COMMAND
BYTE
S
W
ACK
ACK
ACK
ACK
P
7 bits
1b
0
1b
0
8 bits
1b
0
8 bits
1b
0
8 bits
1b
0
MSB LSB
MSB LSB
MSB LSB
MSB LSB
ChargerMode() = 0x12
ChargingCurrent() = 0x14
ChargerVoltage() = 0x15
AlarmWarning() = 0x16
Preset to
0b0001001
D7
D0
D15
D8
b) Read-Word Format
SLAVE
LOW
DATA
BYTE
HIGH
DATA
BYTE
COMMAND
ACK
SLAVE
ADDRESS
S
W
ACK
S
R
ACK
ACK
NACK P
ADDRESS
BYTE
7 bits
1b 1b
8 bits
1b
0
7 bits
1b 1b
8 bits
1b
0
8 bits
1b
1
MSB LSB
0
0
MSB LSB
MSB LSB
1
0
MSB LSB
MSB LSB
Preset to
0b0001001
Preset to
0b0001001
D7
D0
D15
D8
ChargerSpecInfo() =
0x11
ChargerStatus() =
0x13
Legend:
S = Start Condition or Repeated Start Condition
ACK = Acknowledge (logic low)
W = Write Bit (logic low)
P = Stop Condition
NACK = NOT Acknowledge (logic high)
R = Read Bit (logic high)
MASTER TO SLAVE
SLAVE TO MASTER
Figure 3. SMBus Write-Word and Read-Word Protocols
______________________________________________________________________________________ 15
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
MOST SIGNIFICANT
ADDRESS BIT (A6)
CLOCKED INTO SLAVE
A5 CLOCKED
INTO SLAVE
A4 CLOCKED
INTO SLAVE
A3 CLOCKED
INTO SLAVE
START
CONDITION
SCL
SDA
t
t
t
HIGH
LOW
HD:STA
t
t
t
HD:DAT
t
t
SU:DAT
SU:STA
HD:DAT
SU:DAT
Figure 4. SMBus Serial Interface Timing—Address
MOST SIGNIFICANT BIT
OF DATA CLOCKED
INTO MASTER
ACKNOWLEDGE
BIT CLOCKED
INTO MASTER
R/W BIT
CLOCKED
INTO SLAVE
SCL
SDA
SLAVE PULLING
SDA LOW
t
t
DV
DV
Figure 5. SMBus Serial Interface Timing—Acknowledgment
16 ______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Table 1. ChargerSpecInfo()*
BIT
0
NAME
CHARGER_SPEC
CHARGER_SPEC
CHARGER_SPEC
CHARGER_SPEC
SELECTOR_SUPPORT
Reserved
DESCRIPTION
Returns a 1 for version 1.0
Returns a zero for version 1.0
Returns a zero for version 1.0
Returns a 1 for version 1.0
1
2
3
4
Returns a zero, indicating no smart battery selector functionality
5
Returns a zero
Returns a zero
Returns a zero
Returns a zero
Returns a zero
Returns a zero
Returns a zero
Returns a zero
Returns a zero
Returns a zero
Returns a zero
6
Reserved
7
Reserved
8
Reserved
9
Reserved
10
11
12
13
14
15
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
*Command: 0x11
______________________________________________________________________________________ 17
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Table 2. ChargerMode()*
BIT
0
NAME
FUNCTION
0* = Allow normal operation; clear the CHG_INHIBITED flip-flop.
1 = Turn off the charger; set the CHG_INHIBITED flip-flop.
The CHG_INHIBITED flip-flop is not affected by any other commands.
INHIBIT_CHARGE
ENABLE_POLLING
POR_RESET
1
Not implemented.
0 = No change.
2
1 = Change the ChargingVoltage() to 0xFFFF and the ChargingCurrent()
to 0x00C0; clear the THERMISTOR_HOT and ALARM_INHIBITED flip-flops.
3
4
RESET_TO_ZERO
Not implemented.
0* = Interrupt on either edge of the AC_PRESENT status bit.
1 = Do not interrupt because of an AC_PRESENT bit change.
AC_PRESENT_MASK
0* = Interrupt on either edge of the BATTERY_PRESENT status bit.
1 = Do not interrupt because of a BATTERY_PRESENT bit change.
5
6
BATTERY_PRESENT_ MASK
POWER_FAIL_MASK
0* = Interrupt on either edge of the POWER_FAIL status bit.
1 = Do not interrupt because of a POWER_FAIL bit change.
7
8
9
—
—
—
Not implemented.
Not implemented.
Not implemented.
0 = The THERMISTOR_HOT status bit does not turn off the charger.
1* = The THERMISTOR_HOT status bit does turn off the charger.
THERMISTOR_HOT is reset by either POR_RESET or
BATTERY_PRESENT = 0 status bit.
10
HOT_STOP
11
12
13
14
15
—
—
—
—
—
Not implemented.
Not implemented.
Not implemented.
Not implemented.
Not implemented.
*Command: 0x12
*State at chip initial power-on (i.e., V
from 0 to +3.3V).
DD
18 ______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Table 3. ChargerStatus()*
BIT
NAME
FUNCTION
0** = Ready to charge smart battery.
0
CHARGE_INHIBITED
1 = Charger is inhibited, I(chg) = 0mA.
This status bit returns the value of the CHG_INHIBITED flip-flop.
1
2
3
4
5
MASTER_MODE
VOLTAGE_NOT_REG
CURRENT_NOT_REG
LEVEL_2
Always returns zero.
Function disabled. Always returns zero.
Function disabled. Always returns zero.
Always returns a 1.
LEVEL_3
Always returns a zero.
0** = The ChargingCurrent() value is valid for the MAX1645B.
1 = The ChargingCurrent() value exceeds the MAX1645B output range,
i.e., programmed ChargingCurrent() exceeds 3008mA.
6
7
CURRENT_OR
VOLTAGE_OR
0 = The ChargingVoltage() value is valid for the MAX1645B.
1** = The ChargingVoltage() value exceeds the MAX1645B output range,
i.e., programmed ChargingVoltage() exceeds 1843mV.
0 = THM is <91% of the reference voltage.
1 = THM is >91% of the reference voltage.
8
9
THERMISTOR_OR
0 = THM is <75.5% of the reference voltage.
1 = THM is >75.5% of the reference voltage.
THERMISTOR_COLD
0 = THM has not dropped to <23.5% of the reference voltage.
1 = THM has dropped to <23.5% of the reference voltage.
THERMISTOR_HOT flip-flop cleared by BATTERY_PRESENT = 0 or writing a 1 into the
POR_RESET bit in the ChargerMode() command.
10
11
THERMISTOR_HOT
THERMISTOR_UR
0 = THM is >7.5% of the reference voltage.
1 = THM is <7.5% of the reference voltage.
Returns the state of the ALARM_INHIBITED flip-flop. This flip-flop is set by either a
watchdog timeout or by writing an AlarmWarning() command with bits 11, 12, 13, 14,
or 15 set. This flip-flop is cleared by BATTERY_PRESENT = 0, writing a 1 into the
POR_RESET bit in the ChargerMode() command, or by receiving successive
ChargingVoltage() and ChargingCurrent() commands. POR: 0.
12
ALARM_INHIBITED
0 = The charging source voltage CVS is above the BATT voltage.
1 = The charging source voltage CVS is below the BATT voltage.
13
14
POWER_FAIL
BATTERY_PRESENT
AC_PRESENT
0 = No battery is present (based on THM input).
1 = Battery is present (based on THM input).
0 = DCIN is below the 7.5V undervoltage threshold.
1 = DCIN is above the 7.5V undervoltage threshold.
15
*Command: 0x13
**State at chip initial power-on.
______________________________________________________________________________________ 19
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Table 4. ChargingCurrent()*
BIT
0
NAME
—
FUNCTION
Not used. Normally a 0.05mV (1mA x 50mΩ) weight.
Not used. Normally a 0.1mV (2mA x 50mΩ) weight.
Not used. Normally a 0.2mV (4mA x 50mΩ) weight.
Not used. Normally a 0.4mV (8mA x 50mΩ) weight.
Not used. Normally a 0.8mV (16mA x 50mΩ) weight.
Not used. Normally a 1.6mV (32mA x 50mΩ) weight.
1
—
2
—
3
—
4
—
5
—
0 = Adds 0mV of charge current-sense voltage.
1 = Adds 3.2mV (64mA x 50mΩ) charge current-sense voltage.
6.4mV (min) (128mA x 50mA) sense voltage.
6
Charge Current, DACI 0
0 = Adds 0mV of charge current-sense voltage.
1 = Adds 6.4mV (128mA x 50mΩ) charge current-sense voltage.
7
8
Charge Current, DACI 1
Charge Current, DACI 2
Charge Current, DACI 3
Charge Current, DACI 4
0 = Adds 0mV of charge current-sense voltage.
1 = Adds 12.8mV (256mA x 50mΩ) charge current-sense voltage.
0 = Adds 0mV of charge current-sense voltage.
1 = Adds 25.6mV (512mA x 50mΩ) charge current-sense voltage.
9
0 = Adds 0mV of charge current-sense voltage.
1 = Adds 51.2mV (1024mA x 50mΩ) charge current-sense voltage.
10
0 = Adds 0mV of charge current-sense voltage.
11
Charge Current, DACI 5
1 = Adds 102.4mV (2048mA x 50mΩ) charge current-sense voltage.
150.4mV (max) (3008mA x 50mA) sense voltage.
0 = Adds 0mV of charge current-sense voltage.
1 = Sets charge current-sense voltage into overrange.
150.4mV (max) (3008mA x 50mA) sense voltage.
12–15
—
*Command: 0x14
ChargingCurrent() (POR: 0x0080)
150.4
102.4
The ChargingCurrent() command uses the write-word
protocol (Figure 3a). The command code for
ChargingCurrent() is 0x14 (0b00010100). The 16-bit
binary number formed by D15–D0 represents the cur-
rent-limit set point (I0) in milliamps. However, since the
MAX1645B has 64mA resolution in setting I0, the D0–D5
bits are ignored as shown in Table 4. Figure 6 shows the
mapping between I0 (the current-regulation-loop set
point) and the ChargingCurrent() code. All codes above
0b00 1011 1100 0000 (3008mA) result in a current over-
range, limiting the charger current to 3.008A. All codes
below 0b0000 0000 1000 0000 (128mA) turn the charg-
ing current off. A 50mΩ sense resistor (R2 in Figure 1) is
required to achieve the correct CODE/current scaling.
51.2
6.4
The power-on reset value for the ChargingCurrent() reg-
ister is 0x0080; thus, the first time a MAX1645B is pow-
ered on, the BATT current regulates to 128mA. Any time
0x0400
0XFFFF
0x0080
0x0800
0x0BC0
Figure 6. Average Voltage Between CSIP and CSIN vs.
ChargingCurrent() Code
20 ______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Table 5. ChargingVoltage()*
PIN
0
BIT NAME
FUNCTION
—
—
—
—
Not used. Normally a 1mV weight.
Not used. Normally a 2mV weight.
Not used. Normally a 4mV weight.
Not used. Normally an 8mV weight.
1
2
3
0 = Adds 0mV of charger-voltage compliance.
1 = Adds 16mV of charger-voltage compliance, 1.024V (min).
4
5
Charge Voltage, DACV 0
Charge Voltage, DACV 1
Charge Voltage, DACV 2
Charge Voltage, DACV 3
Charge Voltage, DACV 4
Charge Voltage, DACV 5
Charge Voltage, DACV 6
Charge Voltage, DACV 7
Charge Voltage, DACV 8
Charge Voltage, DACV 9
Charge Voltage, DACV 10
Charge Voltage, Overrange
0 = Adds 0mV of charger-voltage compliance.
1 = Adds 32mV of charger-voltage compliance, 1.024V (min).
0 = Adds 0mV of charger-voltage compliance.
1 = Adds 64mV of charger-voltage compliance, 1.024V (min).
6
0 = Adds 0mV of charger-voltage compliance.
1 = Adds 128mV of charger-voltage compliance, 1.024V (min).
7
0 = Adds 0mV of charger-voltage compliance.
1 = Adds 256mV of charger-voltage compliance, 1.024V (min).
8
0 = Adds 0mV of charger-voltage compliance.
1 = Adds 512mV of charger-voltage compliance, 1.024V (min).
9
0 = Adds 0mA of charger-voltage compliance.
1 = Adds 1024mV of charger-voltage compliance.
10
11
12
13
14
15
0 = Adds 0mV of charger-voltage compliance.
1 = Adds 2048mV of charger-voltage compliance.
0 = Adds 0mV of charger-voltage compliance.
1 = Adds 4096mV of charger-voltage compliance.
0 = Adds 0mV of charger-voltage compliance.
1 = Adds 8192mV of charger-voltage compliance.
0 = Adds 0mV of charger-voltage compliance.
1 = Adds 16384mV of charger-voltage compliance, 18432mV (max).
0 = Adds 0mV of charger-voltage compliance.
1 = Sets charger compliance into overrange, 18432mV.
*Command: 0x15
the battery is removed, the ChargingCurrent() register
returns to its power-on reset state.
MAX1645B has 16mV resolution in setting V0, the D0,
D1, D2, and D3 bits are ignored as shown in Table 5.
The ChargingVoltage() command is used to set the bat-
tery charging voltage compliance from 1.024V to
18.432V. All codes greater than or equal to 0b0100
1000 0000 0000 (18432mV) result in a voltage over-
range, limiting the charger voltage to 18.432V. All codes
below 0b0000 0100 0000 0000 (1024mV) terminate
charge. Figure 7 shows the mapping between V0
ChargingVoltage() (POR: 0x4800)
The ChargingVoltage() command uses the write-word
protocol (Figure 3a). The command code for
ChargingVoltage() is 0x15 (0b00010101). The 16-bit
binary number formed by D15–D0 represents the volt-
age set point (V0) in millivolts; however, since the
______________________________________________________________________________________ 21
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
18.432V
16.800V
V
= 4.096V
REF
VDCIN > 20V
12.592V
8.400V
4.192V
1.024V
0
0
0x0400
0xFFFF
0x106x
0x20Dx
0x313x
0x41A0 0x4800
ChargingVoltage() D15–D0 DATA
Figure 7. ChargingVoltage() Code to Voltage Mapping
(the voltage-regulation-loop set point) and the
ChargingVoltage() code.
AlarmWarning() is 0x16 (0b00010110). AlarmWarning()
sets the ALARM_INHIBITED status bit in the MAX1645B
if D15, D14, D13, D12, or D11 of the write-word protocol
data equals 1. Table 6 summarizes the Alarm-Warning()
command’s function. The ALARM_INHIBITED status bit
remains set until the battery is removed, a
ChargerMode() command is written with the
POR_RESET bit set, or new ChargingCurrent() AND
ChargingVoltage() values are written. As long as
ALARM_INHIBITED = 1, the MAX1645B switching regu-
lators remain off.
The power-on reset value for the ChargingVoltage() reg-
ister is 0x4880; thus, the first time a MAX1645B is pow-
ered on, the BATT voltage regulates to 18.432V. Any
time the battery is removed, the ChargingVoltage() reg-
ister returns to its power-on reset state. The voltage at
DAC corresponds to the set compliance voltage divided
by 4.5.
AlarmWarning() (POR: Not Alarm)
The AlarmWarning() command uses the write-word
protocol (Figure 3a). The command code for
22 ______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Table 6. AlarmWarning()*
BIT
0
BIT NAME
Error Code
FUNCTION
Not used
Not used
Not used
Not used
Not used
Not used
Not used
Not used
Not used
Not used
Not used
1
Error Code
2
Error Code
3
Error Code
4
FULLY_DISCHARGED
FULLY_CHARGED
DISCHARGING
5
6
7
INITIALIZING
8
REMAINING_TIME_ ALARM
REMAINING_CAPACITY_ ALARM
Reserved
9
10
0 = Charge normally
1 = Terminate charging
11
12
13
14
15
TERMINATE_ DISCHARGE_ALARM
OVER_TEMP_ALARM
0 = Charge normally
1 = Terminate charging
0 = Charge normally
1 = Terminate charging
OTHER_ALARM
0 = Charge normally
1 = Terminate charging
TERMINATE_CHARGE_ ALARM
OVER_CHARGE_ALARM
0 = Charge normally
1 = Terminate charging
*Command: 0x16
______________________________________________________________________________________ 23
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
MOSFET Drivers
Interrupts and Alert Response Address
The MAX1645B requests an interrupt by pulling the INT
pin low. An interrupt is normally requested when there is
a change in the state of the ChargerStatus() bits
POWER_FAIL (bit 13), BATTERY_PRESENT (bit 14), or
AC_PRESENT (bit 15). Therefore, the INT pin pulls low
whenever the AC adapter is connected or disconnect-
ed, the battery is inserted or removed, or the charger
goes in or out of dropout. The interrupts from each of
the ChargerStatus() bits can be masked by an associat-
ed ChargerMode() bit POWER_FAIL_MASK (bit 6), BAT-
TERY_PRESENT_MASK (bit 5), or AC_PRESENT_MASK
(bit 4).
The low-side driver output DLO swings from 0V to DLOV.
DLOV is usually connected through a filter to LDO. The
high-side driver output DHI is bootstrapped off LX and
swings from V to V
. When the low-side driver turns
on, BST rises to one diode voltage below DLOV.
LX
BST
Filter DLOV with an RC circuit whose cutoff frequency
is about 50kHz. The configuration in Figure 1 intro-
duces a cutoff frequency of around 48kHz:
f = 1 / 2πRC = 1 / (2 ✕ π ✕ 33Ω ✕ 0.1µF) = 48kHz
Thermistor Comparators
Four thermistor comparators evaluate the voltage at the
THM input to determine the battery temperature. This
input is meant to be used with the internal thermistor
connected to ground inside the battery pack. Connect
the output of the battery thermistor to THM. Connect a
All interrupts are cleared by sending any command to
the MAX1645B, or by sending a command to the
AlertResponse() address, 0x19, using a modified
receive-byte protocol. In this protocol, all devices that
set an interrupt try to respond by transmitting their
address, and the device with the highest priority, or
most leading zeros, are recognized and cleared. The
process repeats until all devices requesting interrupts
are addressed and cleared. The MAX1645B responds
to the AlertResponse() address with 0x13, which is its
address and a trailing 1.
resistor from THM to V . The resistor-divider sets the
DD
voltage at THM. When the charger is not powered up,
the battery temperature can still be determined if V
powered from an external voltage source.
is
DD
Thermistor Bits
Figure 9 shows the expected electrical behavior of a
103ETB-type thermistor (nominally 10kΩ at +25°C 5%
or better) to be used with the MAX1645B:
Charger Timeout
The MAX1645B includes a timer that terminates charge
if the charger has not received a ChargingVoltage() or
ChargingCurrent() command in 175s. During charging,
the timer is reset each time a ChargingVoltage() or
ChargingCurrent() command is received; this ensures
that the charging cycle is not terminated.
• THERMISTOR_OR bit is set when the thermistor
value is >100kΩ. This indicates that the thermistor is
open or a battery is not present. The charger is set to
POR, and the BATTERY_PRESENT bit is cleared.
• THERMISTOR_COLD bit is set when the thermistor
value is >30kΩ. The thermistor indicates a cold bat-
tery. This bit does not affect the charge.
If timeout occurs, charging terminates and both
ChargingVoltage() and ChargingCurrent() commands
are required to restart charging. A power-on reset also
restarts charging at 128mA.
• THERMISTOR_HOT bit is set when the thermistor
value is <3kΩ. This is a latched bit and is cleared by
removing the battery or sending a POR with the
ChargerMode() command. The MAX1645B charger
is stopped unless the HOT_STOP bit is cleared in the
ChargerMode() command or the RES_UR bit is set.
See Table 7.
DC-to-DC Converter
The MAX1645B employs a buck regulator with a boot-
strapped NMOS high-side switch and a low-side NMOS
synchronous rectifier.
• THERMISTOR_UR bit is set when the thermistor
value is <500Ω (i.e., THM is grounded).
DC-to-DC Controller
The control scheme is a constant off-time, variable-fre-
quency, cycle-by-cycle current mode. The off-time is
Multiple bits can be set depending on the value of the
thermistor (e.g., a thermistor that is 450Ω causes both
the THERMISTOR_HOT and the THERMISTOR_UR bits
to be set). The thermistor can be replaced by fixed-
value resistors in battery packs that do not require the
thermistor as a secondary fail-safe indicator. In this
case, it is the responsibility of the battery pack to manip-
ulate the resistance to obtain correct charger behavior.
constant for a given BATT voltage; it varies with V
BATT
to keep the ripple current constant. During low-dropout
operation, a maximum on-time of 10ms allows the con-
troller to achieve >99% duty cycle with continuous con-
duction. Figure 8 shows the controller functional
diagram.
24 ______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
10ms
S
CSSP
ADAPTER IN
LDO
RESET
3.0V
BST
R1
CSS
IMAX
CCMP
IMIN
MAX1645B
CSSN
BST
R
Q
DHI
LX
R
S
Q
C
DHI
BST
CHG
Q
L1
R2
0.25V
0.1V
DLO
DLO
1µs
CSIP
ZCMP
CSI
CSIN
BATT
GMS
GMI
LVC
C
OUT
BATTERY
R
FC
70kΩ
GMV
R
FI
20kΩ
DACV
DACI
CLS
CONTROL
ON
CCS
CCI
CCV
*
*
*OPTIONAL
Figure 8. DC-to-DC Converter Functional Diagram
______________________________________________________________________________________ 25
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Load and Source Switch Drivers
1000
The MAX1645B can drive two P-channel MOSFETs to
eliminate voltage drops across the Schottky diodes,
which are normally used to switch the load current from
the battery to the main DC source:
100
10
1
• The source switch P1 is controlled by PDS. This P-
channel MOSFET is turned on when CVS rises to
300mV above BATT and turns off when CVS falls to
100mV above BATT. The same signal that controls
the PDS also sets the POWER_FAIL bit in the
Charger Status() register. See Operating Conditions.
0.1
• Load switch P2 is controlled by PDL. This P-channel
MOSFET is turned off when the CVS rises to 100mV
below BATT and turns on when CVS falls to 300mV
below BATT.
-40
-50
-30 -20 -10
0
10 20 30 40 50 60 70 80 90 100 110
TEMPERATURE (°C)
Figure 9. Typical Thermistor Characteristics
Dropout Operation
The MAX1645B has a 99.99% duty-cycle capability
with a 10ms maximum on-time and 1µs off-time. This
allows the charger to achieve dropout performance lim-
ited only by resistive losses in the DC-DC converter
components (P1, R1, N1, R2; see Figure 1). The actual
dropout voltage is limited to 300mV between CVS and
BATT by the power-fail comparator (see Operating
Conditions).
typically found in notebook computers, video cameras,
cellular phones, or other portable electronic equipment.
Another configuration uses two or more smart batteries
(Figure 11). The smart battery selector is used either to
connect batteries to the smart battery charger or the
system, or to disconnect them, as appropriate. For
each battery, three connections must be made: power
(the battery’s positive and negative terminals), the
SMBus (clock and data), and the safety signal (resis-
tance, typically temperature dependent). Additionally,
the system host must be able to query any battery so it
can display the state of all batteries present in the system.
Applications Information
Smart Battery Charging
System/Background Information
A smart battery charging system, at a minimum, con-
sists of a smart battery and smart battery charger com-
patible with the Smart Battery System Specifications
using the SMBus.
Figure 11 shows a two-battery system where battery 2 is
being charged while battery 1 is powering the system.
This configuration can be used to “condition” battery 1,
allowing it to be fully discharged prior to recharge.
A system can use one or more smart batteries. Figure 10
shows a single-battery system. This configuration is
Table 7. Thermistor Bit Settings
THERMISTOR
DESCRIPTION
STATUS BIT
CONTROLLED
WAKE-UP CHARGE
CHARGE
RES_UR and RES_HOT
RES_HOT
Underrange
Hot
Allowed for timeout period
Not allowed
Allowed
Not allowed
Allowed
(None)
Normal
Allowed for timeout period
Allowed for timeout
period
RES_COLD
Cold
Allowed
RES_OR and RES_COLD
Overrange
Float charge*
Not allowed
*See Battery Present in the Operating Conditions section for more information.
26 ______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
V
CC
SYSTEM
POWER
CONTROL
SYSTEM
POWER
SUPPLY
DC (UNREGULATED) / V
+12V, -12V
BATTERY
AC
AC-DC
V
DC (UNREGULATED)
BATTERY
CONVERTER
(UNREGULATED)
SAFETY
SIGNAL
SMART
BATTERY
MAX1645B
SYSTEM HOST
(SMBus HOST)
SMART BATTERY
CHARGER
CRITICAL EVENTS
CHARGING VOLTAGE/CURRENT
REQUESTS
SMBus
BATTERY DATA/STATUS REQUESTS
CRITICAL EVENTS
Figure 10. Typical Single Smart Battery System
The smart battery is in the best position to tell the smart
battery charger how it needs to be charged. The charg-
ing algorithm in the battery may request a static charge
condition or may choose to periodically adjust the
smart battery charger’s output to meet its present
needs. A Level 2 smart battery charger is truly chem-
istry independent and, since it is defined as an SMBus
slave device only, the smart battery charger is relatively
inexpensive and easy to implement.
Smart Battery Charger Types
Two types of smart battery chargers are defined: Level
2 and Level 3. All smart battery chargers communicate
with the smart battery using the SMBus; the two types
differ in their SMBus communication mode and whether
they modify the charging algorithm of the smart battery
(Table 8). Level 3 smart battery chargers are supersets
of Level 2 chargers and, as such, support all Level 2
charger commands.
Selecting External Components
Table 9 lists the suppliers’ contacts; Table 10 lists the
recommended components and refers to the circuit of
Figure 1. The following sections describe how to select
these components.
Level 2 Smart Battery Charger
The Level 2 or smart battery-controlled smart battery
charger interprets the smart battery’s critical warning
messages and operates as an SMBus slave device to
respond to the smart battery’s ChargingVoltage() and
ChargingCurrent() messages. The charger is obliged to
adjust its output characteristics in direct response to
the ChargingVoltage() and ChargingCurrent() mes-
sages it receives from the battery. In Level 2 charging,
the smart battery is completely responsible for initiating
the communication and providing the charging algo-
rithm to the charger.
MOSFETs and Schottky Diodes
Schottky diode D1 provides power to the load when the
AC adapter is inserted. Choose a 3A Schottky diode or
higher. This diode may not be necessary if P1 is used.
The P-channel MOSFET P1 turns on when V
BATT
>
CVS
V
. This eliminates the voltage drop and power con-
______________________________________________________________________________________ 27
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
AC
V
CC
SYSTEM
POWER
SUPPLY
+12V, -12V
DC (UNREGULATED) / V
BATTERY
NOTE: SB 1 POWERING SYSTEM
SB 2 CHARGING
AC-DC
CONVERTER
(UNREGULATED)
SMART BATTERY 1
SMART BATTERY 2
SMBus
MAX1645B
SYSTEM HOST
(SMBus HOST)
SAFETY SIGNAL
SMART BATTERY
SELECTOR
SMART
BATTERY
CHARGER
V
CHARGE
CRITICAL EVENTS
SMBus
BATTERY DATA/STATUS REQUESTS
Figure 11. Typical System Using Multiple Smart Batteries
sumption of the Schottky diode. To minimize power loss,
select a MOSFET with an R
MOSFET must be able to deliver the maximum current
as set by R1. D1 and P1 provide protection from
reversed voltage at the adapter input.
Table 8. Smart Battery Charger Type
by SMBus Mode and Charge Algorithm
Source
of 50mΩ or less. This
DS(ON)
CHARGE ALGORITHM SOURCE
N-channel MOSFETs N1 and N2 are the switching
devices for the buck controller. High-side switch N1
should have a current rating of at least 6A and have an
SMBus MODE
MODIFIED FROM
BATTERY
BATTERY
R
of 50mΩ or less. The driver for N1 is powered
Slave only
Level 2
Level 3
Level 3
Level 3
DS(ON)
by BST; its current should be less than 10mA. Select a
MOSFET with a low total gate charge and determine the
Slave/master
Note: Level 1 smart battery chargers were defined in the ver-
sion 0.95a specification. While they can correctly interpret
smart battery end-of-charge messages, minimizing over-
charge, they do not provide truly chemistry-independent
charging. They are no longer defined by the Smart Battery
Charger Specification and are explicitly not compliant with this
and subsequent smart battery charger specifications.
required drive current by I
= Q
✕ f (where f is
GATE
GATE
the DC-to-DC converter maximum switching frequency
of 400kHz).
The low-side switch N2 should also have a current rating
of at least 3A, have an R
of 100mΩ or less, and a
DS(ON)
total gate charge less than 10nC. N2 is used to provide
the starting charge to the BST capacitor C14. During nor-
mal operation, the current is carried by Schottky diode
D2. Choose a 3A or higher Schottky diode.
28 ______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
D3 is a signal-level diode, such as the 1N4148. This
diode provides the supply current to the high-side
MOSFET driver.
Other Components
CCV, CCI, and CCS are the compensation points for the
three regulation loops. Bypass CCV with a 10kΩ resistor
in series with a 0.01µF capacitor to GND. Bypass CCI
and CCS with 0.01µF capacitors to GND. R7 and R13
serve as protection resistors to THM and CVS, respec-
tively. To achieve acceptable accuracy, R6 should be
10kΩ and 1% to match the internal battery thermistor.
The P-channel MOSFET P2 delivers the current to the
load when the AC adapter is removed. Select a
MOSFET with an R
of 50mΩ or less to minimize
DS(ON)
power loss and voltage drop.
Inductor Selection
Current-Sense Input Filtering
In normal circuit operation with typical components, the
current-sense signals can have high-frequency tran-
sients that exceed 0.5V due to large current changes
and parasitic component inductance. To achieve prop-
er battery and input current compliance, the current-
sense input signals should be filtered to remove large
common-mode transients. The input current-limit sens-
ing circuitry is the most sensitive case due to large cur-
rent steps in the input filter capacitors (C1 and C2) in
Figure 1. Use 1µF ceramic capacitors from CSSP and
CSSN to GND. Smaller 0.1µF ceramic capacitors can
be used on the CSIP and CSIN inputs to GND since the
current into the battery is continuous. Place these
capacitors next to the single-point ground directly
under the MAX1645B.
Inductor L1 provides power to the battery while it is
being charged. It must have a saturation current of at
least 3A plus one-half of the current ripple (∆I ):
L
1
I
= 3A + /2 ∆I
SAT
L
The controller determines the constant off-time period,
which is dependent on BATT voltage. This makes the
ripple current independent of input and battery voltage
and should be kept to less than 1A. Calculate the ∆I
L
with the following equation:
∆I = 21Vµs / L
L
Higher inductor values decrease the ripple current.
Smaller inductor values require higher saturation cur-
rent capabilities and degrade efficiency. Typically, a
22µH inductor is ideal for all operating conditions.
Layout and Bypassing
Bypass DCIN with a 1µF to GND (Figure 1). D4 protects
the device when the DC power source input is
reversed. A signal diode for D4 is adequate as DCIN
only powers the LDO and the internal reference.
Bypass LDO, BST, DLOV, and other pins as shown in
Figure 1.
Table 9. Component Suppliers
COMPONENT
MANUFACTURER
Sumida
PART
CDRH127 series
D03316P series
UP2 series
Good PC board layout is required to achieve specified
noise, efficiency, and stable performance. The PC
board layout artist must be given explicit instructions,
preferably a pencil sketch showing the placement of
power-switching components and high-current routing.
A ground plane is essential for optimum performance.
In most applications, the circuit is located on a multilay-
er board, and full use of the four or more copper layers
is recommended. Use the top layer for high-current
connections, the bottom layer for quiet connections
Inductor
Coilcraft
Coiltronics
Internal Rectifier
Fairchild
IRF7309
MOSFET
FDS series
Vishay-Siliconix
Dale
Si4435/6
WSL series
Sense resistor
Capacitor
IRC
LR2010-01 series
(REF, CCV, CCI, CCS, DAC, DCIN, V , and GND),
DD
and the inner layers for an uninterrupted ground plane.
TPS series,
TAJ series
AVX
Use the following step-by-step guide:
Sprague
Motorola
Nihon
595D series
1) Place the high-power connections first, with their
grounds adjacent:
1N5817–1N5822
NSQ03A04
Diode
• Minimize current-sense resistor trace lengths and
ensure accurate current sensing with Kelvin con-
nections.
Central
Semiconductor
CMSH series
______________________________________________________________________________________ 29
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Table 10. Component Selection
DESIGNATION
C1, C2 input capacitors
DESCRIPTION
22µF, 35V low-ESR tantalum capacitors
AVX TPSE226M035R0300
22µF, 25V low-ESR tantalum capacitors
AVX TPSD226M025R0200
C3, C4 output capacitors
C5, C19, C20
1µF, >30V ceramic capacitors
1µF ceramic capacitors
C6, C7, C12
C8, C14, C16
0.1µF ceramic capacitors
0.01µF ceramic capacitor
1nF ceramic capacitors
C9 compensation capacitor
C10, C11 compensation capacitors
C13
1500pF ceramic capacitor
0.1µF, >20V ceramic capacitors
0.1µF, >30V ceramic capacitor
C18, C24
C23
40V, 2A Schottky diodes
Central Semiconductor CMSH2-40
D1, D2
D3, D4
L1
Small-signal diodes
Central Semiconductor CMPSH-3
22µH, 3.6A buck inductor
Sumida CDRH127-220
30V, 11.5A, high-side N-channel MOSFET (8-pin SO)
Fairchild FDS6680
30V, 8.4A, low-side N-channel MOSFET
N1 high-side MOSFET
N2 low-side MOSFET
Fairchild FDS6612A or
30V, signal-level N-channel MOSFET
2N7002
30V, 11A P-channel MOSFETs load and source switches
Fairchild FDS6675
P1, P2
R1
40mΩ 1%, 0.5W battery current-sense resistor
Dale WSL-2010/40mΩ/ 1%
50mΩ 1%, 0.5W source current-sense resistor
Dale WSL-2010/50mΩ/ 1%
R2
R3, R4
R3 + R4 >100kΩ input current-limit setting resistors
10kΩ 5% resistors
R5, R7–R10, R17, R18
R6
10kΩ 1% temperature sensor network resistor
1Ω 5% resistors
R11, R16
R12
33Ω 5% resistor
R13
1kΩ 5% resistor
R14, R15
4.7Ω 5% resistors
Note: See Figure 1 for circuit configuration.
30 ______________________________________________________________________________________
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
• Minimize ground trace lengths in the high-current
2) Place the IC and signal components. Keep the main
switching nodes (LX nodes) away from sensitive ana-
log components (current-sense traces and REF
capacitor). Important: The IC must be no further
than 10mm from the current-sense resistors.
paths.
• Minimize other trace lengths in the high-current
paths:
• Use >5mm-wide traces.
Keep the gate drive traces (DHI, DLO, and BST)
shorter than 20mm and route them away from the
current-sense lines and REF. Place ceramic bypass
capacitors close to the IC. The bulk capacitors can
be placed further away. Place the current-sense
input filter capacitors under the part, connected
directly to the GND pin.
• Connect C1 and C2 to high-side MOSFET
(10mm (max) length).
• Connect rectifier diode cathode to low-side
MOSFET (5mm (max) length).
• LX node (MOSFETs, rectifier cathode, inductor:
15mm (max) length). Ideally, surface-mount
power components are flush against one another
with their ground terminals almost touching.
These high-current grounds are then connected
to each other with a wide, filled zone of top-
layer copper so they do not go through vias.
The resulting top-layer subground plane is con-
nected to the normal inner-layer ground plane
at the output ground terminals, which ensures
that the IC’s analog ground is sensing at the
supply’s output terminals without interference
from IR drops and ground noise. Other high-
current paths should also be minimized, but
focusing primarily on short ground and current-
sense connections eliminates about 90% of all
PC board layout problems.
3) Use a single-point star ground placed directly below
the part. Connect the input ground trace, power
ground (subground plane), and normal ground to
this node.
Chip Information
TRANSISTOR COUNT: 6996
______________________________________________________________________________________ 31
Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting
Typical Operating Circuit
ADAPTER IN
PDS
CVS
DCIN
CSSP
MAX1645B
REF
CLS
GND
CSSN
LDO
LOAD
BST
DLOV
DAC
CCV
DHI
LX
CCI
CCS
DLO
PGND
CSIP
CSIN
PDL
BATT
BATTERY
HOST
THM
V
DD
SCL
SDA
INT
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
32 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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