AAT2550ISK-CAA-T1 [ANALOGICTECH]
Total Power Solution for Portable Applications; 用于便携式应用的总电源解决方案
| 型号： | AAT2550ISK-CAA-T1 |
| 厂家： | 
ADVANCED ANALOGIC TECHNOLOGIES |
| 描述： | Total Power Solution for Portable Applications |
| 文件： | 总35页 (文件大小：902K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
AAT2550
Total Power Solution for Portable Applications
™
SystemPower
General Description
Features
The AAT2550 is a fully integrated total power solu-
tion with two step-down converters plus a single-
cell lithium-ion / polymer battery charger. The step-
down converter input voltage range spans 2.7V to
5.5V, making the AAT2550 ideal for systems pow-
ered by single-cell lithium-ion/polymer batteries.
•
Two Step-Down Converters:
— 600mA Output Current per Converter
— VIN Range: 2.7V to 5.5V
— 1.4MHz Switching Frequency
— Low RDS(ON) 0.4Ω Integrated Power
Switches
— Internal Soft Start
The battery charger is a complete constant current/
constant voltage linear charger. It offers an inte-
grated pass device, reverse blocking protection,
high current accuracy and voltage regulation,
charge status, and charge termination. The charg-
ing current is programmable via external resistor
from 100mA to 1A. In addition to these standard
features, the device offers over-voltage, over-cur-
rent, and thermal protection.
— 27µA Quiescent Current per Converter
Highly Integrated Battery Charger:
— Programmable Charging Current from
100mA to 1A
•
•
— Pass Device
— Reverse Blocking Diodes
— Current Sensing Resistor
— Digital Thermal Regulation
Short-Circuit, Over-Temperature, and Current
Limit Protection
The two step-down converters are highly integrated,
operating at a switching frequency of 1.4MHz, mini-
mizing the size of external components while keep-
ing switching losses low. Each converter has inde-
pendent input, enable, and feedback pins. The out-
put voltage ranges from 0.6V to VIN. Each converter
is capable of delivering up to 600mA of load current.
•
•
QFN44-24 Package
-40°C to +85°C Temperature Range
Applications
The AAT2550 is available in a Pb-free, space-sav-
ing, thermally-enhanced QFN44-24 package and is
rated over the -40°C to +85°C temperature range.
•
•
•
•
Cellular Telephones
Digital Cameras
Handheld Instruments
MP3, Portable Music, and Portable Media
Players
•
PDAs and Handheld Computers
Typical Application
Battery Pack
Batt+
Adapter
ADP
BAT
AAT2550
TS
CT
STAT1
STAT2
Batt-
Serial Interface
DATA
ADPSET
RSET
Temp
VOUTA
COUTA
LXA
ENBAT
INA
FBA
LXB
Li-Ion Battery or
Adapter
INB
VOUTB
COUTB
ENA
ENB
FBB
GND
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AAT2550
Total Power Solution for Portable Applications
Pin Descriptions
Pin #
Symbol Function
1
ENA
Enable pin for Converter A. When connected to logic low, it disables the step-down converter
and consumes less than 1µA of current. When connected to logic high, the converter operates
normally.
2
LXA
Power switching node for Converter A. Connect the inductor to this pin. Internally, it is connect-
ed to the drain of both high- and low-side MOSFETs.
3, 17
PGND
Power ground. Connect the PGND pins together as close to the IC as possible. Connect
AGND to PGND at a single point as close to the IC as possible.
Status report to the microcontroller via serial interface (open drain).
Not connected.
4
5, 7
6
DATA
N/C
ADPSET
Charge current set point. Connect a resistor from this pin to ground. Refer to Typical
Characteristics curves for resistor selection.
8
BAT
ADP
Battery charging and sensing. Connect the positive terminal of the battery to BAT.
Input for adapter charger.
9
10, 11, 22
12
AGND
ENBAT
Analog signal ground. Connect AGND to PGND at a single point as close to the IC as possible.
Enable pin for the battery charger. When connected to logic low, the battery charger is dis-
abled and consumes less than 1µA of current. When connected to logic high, the charger
operates normally.
13
14
15
16
TS
Temperature sense input. Connect to a 10kΩ NTC thermistor.
Battery charge status indicator pin to drive an LED. It is an open drain input.
Battery charge status indicator pin to drive an LED. It is an open drain input.
Timing capacitor to adjust internal watchdog timer. Sets maximum charge time for adapter
powered trickle, constant current, and constant voltage charge modes.
Power switching node for Converter B. Connect the inductor to this pin. Internally, it is connect-
ed to the drain of both high- and low-side MOSFETs.
STAT2
STAT1
CT
18
19
LXB
ENB
Enable pin for Converter B. When connected to logic low, it disables the step-down converter
and consumes less than 1µA of current. When connected to logic high, the converter operates
normally.
20
21
INB
Input voltage for Converter B.
FBB
Output voltage feedback input for Converter B. FBB senses the output voltage for regulation
control. For fixed output versions, connect FBB to the output voltage. For adjustable versions,
drive FBB from the output voltage through a resistive voltage divider. The FBB regulation
threshold is 0.6V.
23
FBA
INA
Output voltage feedback input for Converter A. FBA senses the output voltage for regulation
control. For fixed output versions, connect FBA to the output voltage. For adjustable versions,
drive FBA from the output voltage through a resistive voltage divider. The FBA regulation
threshold is 0.6V.
24
Input voltage for Converter A.
EP
Exposed paddle; connect to ground directly beneath the package.
2
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AAT2550
Total Power Solution for Portable Applications
Pin Configuration
QFN44-24
(Top View)
1
2
3
4
5
6
18
17
16
15
14
13
ENA
LXA
PGND
DATA
N/C
LXB
PGND
CT
STAT1
STAT2
TS
ADPSET
Absolute Maximum Ratings1
Symbol
Description
Value
Units
VINA/B, VADP
INA, INB, and ADP Voltages to GND
VLXA, VLXB, VFBA, and VFBB to GND
Voltage on All Other Pins to GND
Operating Junction Temperature Range
-0.3 to 6.0
V
V
VLXA/B, VFBA/B
-0.3 to VINA/B, VADP + 0.3
-0.3 to 6.0
VX
TJ
V
-40 to 150
°C
°C
TLEAD
Maximum Soldering Temperature (at leads, 10 sec)
300
Thermal Information
Symbol
Description
Value
Units
PD
Maximum Power Dissipation
Thermal Resistance2
2.0
50
W
θJA
°C/W
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions
other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Mounted on an FR4 printed circuit board.
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AAT2550
Total Power Solution for Portable Applications
Electrical Characteristics1
VIN = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C.
Symbol
Description
Conditions
Min
Typ
Max Units
Step-Down Converters A and B
VIN
Input Voltage
2.7
5.5
2.7
V
V
VIN Rising
Hysteresis
VIN Falling
VUVLO
Under-Voltage Lockout Threshold
100
mV
V
1.8
-3.0
0.6
I
OUT = 0 to 600mA,
VOUT
Output Voltage Tolerance
3.0
%
VIN = 2.7V to 5.5V
VOUT
IOUT
IQ
Output Voltage Range
Output Current
VIN
600
70
V
mA
µA
µA
A
Per Converter
Quiescent Current
Shutdown Current
P-Channel Current Limit
Each Converter
VENA = VENB = GND
Each Converter
27
ISHDN
ILIM
1.0
0.8
1.0
V
IN = 5.5V, VLX = 0 to VIN,
ILX_LEAK
LX Leakage Current
1.0
0.2
µA
VENA = VENB = GND
VFB = 0.6V
IFB_LEAK
RFB
Feedback Leakage
µA
FB Impedance
VOUT > 0.6V
250
kΩ
Feedback Threshold Voltage Accuracy
(0.6V Adjustable Version)
High-Side Switch On Resistance
Low-Side Switch On Resistance
Line Regulation
VFB
No Load, TA = 25°C
0.591
0.6
0.609
V
RDS(ON)H
RDS(ON)L
ΔVLineReg
FOSC
0.45
0.40
0.1
Ω
Ω
%/V
MHz
°C
°C
V
VIN = 2.7V to 5.5V
Switching Frequency
1.4
TSD
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
Enable Threshold Low
140
15
THYS
VEN(L)
0.6
VEN(H)
Enable Threshold High
1.4
V
1. The AAT2550 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
4
2550.2006.07.1.0
AAT2550
Total Power Solution for Portable Applications
Electrical Characteristics1
VADP = 5V; TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C.
Symbol Description
Battery Charger
Conditions
Min
Typ
Max Units
VADP
Adapter Voltage Range
4.0
5.5
V
V
Under-Voltage Lockout
UVLO Hysteresis
Rising Edge
3.0
150
0.75
0.3
VUVLO
mV
mA
µA
µA
µA
V
IQ
Quiescent Current
ICHARGE = 100mA
VBAT = 4.25V
3.0
1.0
ISLEEP
ILEAKAGE
ISHDN
Sleep Mode Current
Reverse Leakage Current
Shutdown Current
VBAT = 4V, ADP Pin Open
VEN = GND
1.0
1.0
2
VBAT EOC
End of Charge Voltage Accuracy
4.158
2.80
100
4.2
0.5
3.0
4.242
_
ΔVCH/VCH Output Charge Voltage Tolerance
%
VMIN
VRCH
ICH
Preconditioning Voltage Threshold
Battery Recharge Voltage Threshold
Charge Current
3.15
V
VBAT EOC - 0.1
V
_
1000
mA
%
ΔICH/ICH
VADPSET
KIA
Charge Current Regulation Tolerance
ADPSET Pin Voltage
10
2.0
Constant Current Mode
V
Current Set Factor: ICH/IADPSET
Charger Pass Device
4000
0.25
3.0
RDS(ON)
TC
VIN = 5.5V
0.20
0.35
0.4
Ω
Hour
Minute
Hour
V
Constant Current Mode Time-Out
Preconditioning Time-Out
Constant Voltage Mode Time-Out
Output Low Voltage
CT = 100nF, VADP = 5.5V
CT = 100nF, VADP = 5.5V
CT = 100nF, VADP = 5.5V
ISINK = 4mA
TP
25
TV
3.0
VSTAT
ISTAT
STAT Sink Current
8.0
4.4
10
mA
V
VOVP
ITK/ICH
ITERM/ICH
ITS
Over-Voltage Protection
Pre-Charge Current
%
Charge Termination Threshold Current
Current Source from TS Pin
7.5
80
%
70
90
µA
Threshold
310
330
15
350
TS1
TS2
TS Hot Temperature Fault
TS Cold Temperature Fault
mV
Hysteresis
Threshold
2.2
2.3
10
2.4
0.4
V
mV
mA
V
Hysteresis
IDATA
VDATA(H)
VDATA(L)
SQPULSE
TPeriod
FDATA
DATA Pin Sink Current
Input High Threshold
DATA Pin is Active Low
3.0
1.6
Input Low Threshold
V
Status Request Pulse Width
System Clock Period
200
ns
µs
kHz
°C
°C
°C
°C
50
20
Data Output Frequency
Thermal Loop Regulation
Thermal Loop Entering Threshold
TREG
90
TLOOP IN
110
85
_
TLOOP OUT Thermal Loop Exiting Threshold
_
TSD
Over-Temperature Shutdown Threshold
145
1. The AAT2550 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
2. End of Charge Voltage Accuracy is specified over the 0° to 70°C ambient temperature range.
2550.2006.07.1.0
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AAT2550
Total Power Solution for Portable Applications
Typical Characteristics—Step-Down Converter
Efficiency vs. Load
(VOUT = 1.8V; L = 4.7μH)
DC Regulation
(VOUT = 1.8V)
100
90
80
70
60
50
1.0
0.5
VIN = 2.7V
VIN = 4.2V
VIN = 4.2V
VIN = 3.6V
0.0
VIN = 3.6V
-0.5
-1.0
VIN = 2.7V
0.1
1
1
1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 2.5V; L = 6.8μμH)
DC Regulation
(VOUT = 2.5V)
100
90
80
70
60
50
1.0
0.5
VIN = 2.7V
VIN = 4.2V
VIN = 5.0V
VIN = 5.0V
VIN = 4.2V
0.0
VIN = 3.6V
VIN = 3.6V
-0.5
-1.0
VIN = 3.0V
0.1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 3.3V; L = 6.8μH)
DC Regulation
(VOUT = 3.3V; L = 6.8µH)
100
1.0
0.5
VIN = 3.6V
VIN = 5.0V
VIN = 4.2V
90
80
70
60
50
VIN = 4.2V
0.0
VIN = 5.0V
-0.5
-1.0
VIN = 3.6V
0.1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
6
2550.2006.07.1.0
AAT2550
Total Power Solution for Portable Applications
Typical Characteristics—Step-Down Converter
Soft Start
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA)
Line Regulation
(VOUT = 1.8V)
0.40
0.30
0.20
0.10
0.00
-0.10
-0.20
-0.30
-0.40
5.0
4.0
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
VEN
VO
IOUT = 10mA
3.0
2.0
1.0
0.0
-1.0
-2.0
-3.0
-4.0
-5.0
IOUT = 1mA
IOUT = 400mA
IL
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Time (100μμs/div)
Input Voltage (V)
Output Voltage Error vs. Temperature
(VIN = 3.6V; VO = 1.8V; IOUT = 400mA)
Switching Frequency vs. Temperature
(VIN = 3.6V; VOUT = 1.8V)
2.0
1.0
15.0
12.0
9.0
6.0
3.0
0.0
0.0
-3.0
-6.0
-9.0
-12.0
-15.0
-1.0
-2.0
-40
-20
0
20
40
60
80
100
-40
-20
0
20
40
60
80
100
Temperature (°C)
Temperature (°C)
Frequency vs. Input Voltage
No Load Quiescent Current vs. Input Voltage
2.0
1.0
50
45
40
35
VOUT = 1.8V
0.0
25°C
85°C
-1.0
-2.0
-3.0
-4.0
30
25
20
15
10
VOUT = 2.5V
VOUT = 3.3V
-40°C
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Input Voltage (V)
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AAT2550
Total Power Solution for Portable Applications
Typical Characteristics—Step-Down Converter
P-Channel RDS(ON) vs. Input Voltage
N-Channel RDS(ON) vs. Input Voltage
750
700
650
600
550
500
450
400
350
300
750
700
650
600
550
500
450
400
350
300
120°C
100°C
120°C
100°C
85°C
85°C
25°C
25°C
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
Input Voltage (V)
Load Transient Response
(1mA to 300mA; VIN = 3.6V; VOUT = 1.8V;
Load Transient Response
(300mA to 400mA; VIN = 3.6V;
C1 = 10μF; CFF = 100pF)
V
OUT = 1.8V; C1 = 4.7μμF)
2.0
1.90
1.85
1.80
1.75
1.9
1.8
1.7
VO
VO
IO
IO
300mA
400mA
300mA
1mA
IL
0.4
0.3
0.2
0.1
IL
0
Time (50μs/div)
Time (50μs/div)
Load Transient Response
(300mA to 400mA; VIN = 3.6V;
Load Transient Response
(300mA to 400mA; VIN = 3.6V; VOUT = 1.8V;
V
OUT = 1.8V; C1 = 10μμF)
C1 = 10μμF; C4 = 100pF)
1.850
1.90
1.85
1.80
1.75
1.825
1.800
1.775
VO
IO
VO
IO
400mA
400mA
300mA
300mA
0.4
0.3
0.2
0.1
0.4
0.3
0.2
0.1
IL
IL
Time (50μs/div)
Time (50μs/div)
8
2550.2006.07.1.0
AAT2550
Total Power Solution for Portable Applications
Typical Characteristics—Step-Down Converter
Line Response
(VOUT = 1.8V @ 400mA)
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA)
40
20
0.30
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
-0.10
1.82
1.81
1.80
1.79
1.78
1.77
1.76
6.0
5.5
5.0
4.5
4.0
3.5
3.0
VO
0
-20
-40
-60
-80
-100
-120
IL
Time (25μμs/div)
Time (10µs/div)
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 400mA)
40
20
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
VO
0
-20
-40
-60
-80
-100
-120
IL
Time (500ns/div)
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AAT2550
Total Power Solution for Portable Applications
Typical Characteristics—Battery Charger
IFASTCHARGE vs. RSET
Battery Voltage vs. Supply Voltage
4.242
4.221
4.200
4.179
4.158
10000
1000
100
10
1
10
100
100
100
4.5
4.75
5.0
5.25
5.5
RSET (kΩ)
Supply Voltage (V)
End of Charge Voltage Regulation
vs. Temperature
Preconditioning Threshold
Voltage vs. Temperature
4.242
4.221
4.200
4.179
4.158
3.05
3.04
3.03
3.02
3.01
3.00
2.99
2.98
2.97
2.96
2.95
-50
-25
0
25
50
75
100
-50
-25
0
25
50
75
Temperature (°°C)
Temperature (°°C)
Preconditioning ICH vs. Temperature
(ADPSET = 8.06kΩΩ)
Fast Charge Current vs. Temperature
(ADPSET = 8.06kΩΩ)
1100
1080
1060
1040
1020
1000
980
120
110
100
90
960
940
920
900
80
-50
-25
0
25
50
75
-50
-25
0
25
50
75
100
Temperature (°C)
Temperature (°C)
10
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AAT2550
Total Power Solution for Portable Applications
Typical Characteristics—Battery Charger
Charging Current vs. Battery Voltage
(ADPSET = 8.06kΩ; VIN = 5.0V)
Fast Charge Current vs. Supply Voltage
(ADPSET = 8.06kΩΩ)
1200
1.2
1.0
0.8
0.6
0.4
0.2
0.0
VBAT = 3.3V
1000
800
600
400
200
0
VBAT = 3.9V
VBAT = 3.5V
2.5
2.9
3.3
3.7
4.1
4.5
4.5
4.75
5.0
5.25
5.5
5.75
6.0
6.0
100
Battery Voltage (V)
Supply Voltage (V)
VIH vs. Supply Voltage
EN Pin (Rising)
VIL vs. Supply Voltage
EN Pin (Falling)
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
-40°C
+25°C
-40°C
+25°C
+85°C
+85°C
4.2
4.4
4.6
4.8
5.0
5.2
5.4
5.6
5.8
6.0
4.2
4.4
4.6
4.8
5.0
5.2
5.4
5.6
5.8
Supply Voltage (V)
Supply Voltage (V)
Adapter Mode Supply Current
vs. ADPSET Resistor
Counter Timeout vs. Temperature
(CT = 0.1μμF)
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
10
8
6
4
Constant Current
Pre-Conditioning
2
0
-2
-4
-6
-8
-10
1
10
100
1000
-50
-25
0
25
50
75
ADPSET Resistor (kΩ)
Temperature (°C)
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AAT2550
Total Power Solution for Portable Applications
Typical Characteristics—Battery Charger
CT Pin Capacitance vs. Counter Timeout
Temperature Sense Output Current
vs. Temperature
2.0
88
86
84
82
80
78
76
74
72
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Precondition Timeout
Precondition + Constant Current Timeout
or Constant Voltage Timeout
-50
-25
0
25
50
75
100
0
2
4
6
8
10
Time (hours)
Temperature (°°C)
12
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AAT2550
Total Power Solution for Portable Applications
Functional Block Diagram
Reverse Blocking
BAT
ADP
Current
Compare
ADPSET
UVLO
OTP
4.2V
Constant
Current
Charge
Control
ENBAT
CV/Pre-
Charge
STAT2
Charge
Status
STAT1
TS
Watchdog
Timer
80µA
Window
CT
Comparator
INA
FBA
Err.
Amp.
DH
DL
LXA
Logic
Voltage
Reference
Control
Logic
ENA
PGND
INB
FBB
Err.
Amp.
DH
DL
LXB
Logic
Voltage
Reference
Control
Logic
ENB
PGND
device and reverse blocking, it offers a constant
current / constant voltage charge algorithm with a
user-programmable charge current level. The two
step-down converters have been designed to mini-
mize external component size and maximize effi-
ciency over the entire load range. Each converter
has independent enable and input voltage pins and
can provide 600mA of load current.
Functional Description
The AAT2550 is a highly integrated power manage-
ment IC comprised of a battery charger and two
step-down voltage converters. The battery charger
is designed for charging single-cell lithium-ion /
polymer batteries. Featuring an integrated pass
2550.2006.07.1.0
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AAT2550
Total Power Solution for Portable Applications
Status monitor output pins are provided to indicate
the battery charge state by directly driving two
Battery Charger
The battery charger is designed to operate with
standard AC adapter input sources, while requiring
a minimum number of external components. It pre-
cisely regulates charge voltage and current for sin-
gle-cell lithium-ion / polymer batteries.
external LEDs. A serial interface output is also
available to report any one of 12 distinct charge
states to the host system microcontroller / micro-
processor. Battery temperature and charge state
are fully monitored for fault conditions. In the event
of an over-voltage or over-temperature condition,
the device will automatically shut down, protecting
the charging device, control system, and the bat-
tery under charge. In addition to internal charge
controller thermal protection, the charger also
offers a temperature sense feedback function (TS
pin) from the battery to shut down the device in the
event the battery exceeds its own thermal limit dur-
ing charging. All fault events are reported to the
user either by simple status LEDs or via the DATA
pin function.
The adapter charge input constant current level
may be programmed up to 1A for rapid charging
applications. The battery charger features thermal
loop charge reduction. In the event of operating
ambient temperatures exceeding the power dissi-
pation abilities of the device package for a given
constant current charge level, the charge control
will enter into thermal regulation. When the system
thermal regulation becomes active, the pro-
grammed constant current charge amplitude will
automatically decrease to a safe level for the pres-
ent operating conditions. If the ambient tempera-
ture drops to a level sufficient to allow the device to
come out of thermal regulation, then the system will
automatically resume charging at the full pro-
grammed constant current level. This intelligent
thermal management system permits the battery
charger to operate and charge a battery cell safely
over a wide range of ambient conditions, while
maximizing the greatest possible charge current
and minimizing the battery charge time for a given
set of conditions.
Charging Operation
As shown in Figure 1, there are four basic modes
for the battery charge cycle:
1. Pre-conditioning / trickle charge
2. Constant current / fast charge
3. Constant voltage
4. End of charge
Preconditioning
(Trickle Charge)
Phase
Constant Current
Phase
Constant Voltage
Phase
Output Charge
Voltage (VCH
)
Preconditioning
Voltage Threshold
(VMIN
)
Regulation
Current
(ICHARGE(REG)
)
Trickle Charge
and Termination
Threshold
Figure 1: Typical Charge Profile.
14
2550.2006.07.1.0
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Total Power Solution for Portable Applications
goes into a sleep state. The charger will remain in a
sleep state until the battery voltage decreases to a
Battery Preconditioning
Before the start of charging, the charger checks sev-
eral conditions in order to assure a safe charging
environment. The input supply must be above the
minimum operating voltage, or under-voltage lock-
out threshold (VUVLO), for the charging sequence to
begin. Also, the battery temperature, as reported by
a thermistor connected to the TS pin from the bat-
tery, must be within the proper window for safe
charging. When these conditions have been met
and a battery is connected to the BAT pin, the charg-
er checks the state of the battery. If the battery volt-
age is below the preconditioning voltage threshold
(VMIN), then the charge control begins precondition-
ing the battery. The preconditioning trickle charge
current is equal to the fast charge constant current
divided by 10. For example, if the programmed fast
charge current is 1A, then the preconditioning mode
(trickle charge) current will be 100mA. Battery pre-
conditioning is a safety precaution for deeply dis-
charged batteries and also helps to limit power dis-
sipation in the pass transistor when the voltage
across the device is at the greatest potential.
level below the battery recharge voltage threshold
(VRCH). When the input supply is disconnected, the
charger will automatically transition into a power-
saving sleep mode. Consuming only an ultra-low
0.3µA in sleep mode, the charger minimizes battery
drain when it is not charging. This feature is particu-
larly useful in applications where the input supply
level may fall below the battery charge or under-volt-
age lockout level. In such cases where the input volt-
age drops, the device will enter sleep mode and
resume charging automatically once the input sup-
ply has recovered from the fault condition.
Step-Down Converters
The AAT2550 offers two high-performance,
600mA, 1.4MHz step-down converters. Both con-
verters minimize external component size and opti-
mize efficiency over the entire load range. The
fixed output version requires only three external
power components (CIN, COUT, and L) for each con-
verter. The adjustable version is programmed with
external feedback resistors to any voltage ranging
from 0.6V to the input voltage. At dropout, the con-
verter duty cycle increases to 100% and the output
voltage tracks the input voltage minus the RDS(ON)
drop of the P-channel MOSFET.
Fast Charge/Constant Current Charging
Battery preconditioning continues until the voltage on
the BAT pin exceeds the preconditioning voltage
threshold (VMIN). At this point, the charger begins the
constant current fast charging phase. The fast charge
constant current (ICH) amplitude is programmed by
the user via the RSET resistor. The charger remains in
the constant current charge mode until the battery
Input voltage range is 2.7V to 5.5V and each convert-
er's efficiency has been optimized for all load condi-
tions, ranging from no load to 600mA. The internal
error amplifier and compensation provides excellent
transient response, load regulation, and line regula-
tion. Soft start eliminates output voltage overshoot
when the enable or the input voltage is applied.
reaches the voltage regulation threshold, VBAT_EOC
.
Constant Voltage Charging
The system transitions to a constant voltage charging
mode when the battery voltage reaches the output
charge regulation threshold (VBAT_EOC) during the con-
stant current fast charge phase. The regulation voltage
level is factory programmed to 4.2V (±1%). The charge
current in the constant voltage mode drops as the bat-
tery under charge reaches its maximum capacity.
Soft Start / Enable
The internal soft start limits the inrush current dur-
ing start-up. This prevents possible sagging of the
input voltage and eliminates output voltage over-
shoot. Typical start-up time for a 4.7µF output
capacitor and load current of 600mA is 100µs.
The AAT2550 offers independent enable pins for
each converter. When connected to logic low, the
enable input forces the respective step-down con-
verter into a low-power, non-switching, shutdown
state. The total input current during shutdown is
less than 1µA for each channel.
End of Charge Cycle Termination and
Recharge Sequence
When the charge current drops to 7.5% of the pro-
grammed fast charge current level in the constant
voltage mode, the device terminates charging and
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AAT2550
Total Power Solution for Portable Applications
System Operation Flow Chart
ADP
Voltage
Yes
ADP
Yes
UVLO
Yes
Output
ADPP
Switch
On
Test
Power Select
V
P > VUVLO
ADP > VADPP
No
No
Sleep
No
Mode
ADP
Loop
Enable
Timing
Power On
Reset
Fault
Conditions Monitor
Yes
OV, OT
Thermal
Loop Enable
No
Expire
Shutdown
Mode
No
Yes
Battery
Temp. Monitor
No
Yes
Yes
Battery
Device Temp. Monitor
Recharge Test
VRCH > VBAT
No
Temp. Fault
<TS<VTS2
VTS1
TJ > 110°C
Charge
Timer
Safety
Yes
Yes
Thermal Loop
Current
Low Current
Set
Preconditioning Test
VMIN > VBAT
Reduction in ADP
Conditioning
Charging Mode
Charge
No
Current
Current Phase Test
Charging
> VBAT
VCH
Mode
No
Voltage
Yes
Voltage Phase Test
IBAT> IMIN
Charging
Mode
No
Charge
Completed
junction over-temperature threshold is 140°C with
15°C of hysteresis. Once an over-temperature or
over-current fault conditions is removed, the output
voltage automatically recovers.
Current Limit and Over-Temperature
Protection
For overload conditions, the peak input current is
limited. To minimize power dissipation and stresses
under current limit and short-circuit conditions,
switching is terminated after entering current limit
for a series of pulses. Switching is terminated for
seven consecutive clock cycles after a current limit
has been sensed for a series of four consecutive
clock cycles.
Under-Voltage Lockout
The under-voltage lockout circuit prevents the
device from improper operation at low input volt-
ages. Internal bias of all circuits is controlled via the
VIN input. Under-voltage lockout (UVLO) guaran-
tees sufficient VIN bias and proper operation of all
internal circuitry prior to activation.
Thermal protection completely disables switching
when internal dissipation becomes excessive. The
16
2550.2006.07.1.0
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Total Power Solution for Portable Applications
When power is re-applied to the adapter pin or the
UVLO condition recovers and ADP > VBAT, the sys-
tem charge control will assess the state of charge
on the battery cell and will automatically resume
charging in the appropriate mode for the condition
of the battery.
Application Information
AC Adapter Power Charging
The adapter constant current charge levels can be
programmed up to 1A. The AAT2550 will operate
from the adapter input over a 4.0V to 5.5V range.
The constant current fast charge current for the
adapter input mode is set by the RSET resistor con-
nected between the ADPSET and ground. Refer to
Table 1 for recommended RSET values for a desired
constant current charge level. The precise charging
function in the adapter mode may be read from the
DATA pin and/or status LEDs. Please refer to the
Battery Charge Status Indication discussion in this
datasheet for further details on data reporting.
ADP
ICH
RSET (kΩ)
100
200
300
400
500
600
700
800
900
1000
84.5
43.2
28.0
21.0
16.9
13.3
11.5
10.2
9.09
8.06
Thermal Loop Control
Due to the integrated nature of the linear charging
control pass device, a special thermal loop control
system has been employed to maximize charging
current under all operation conditions. The thermal
management system measures the internal circuit
die temperature and reduces the fast charge cur-
rent when the device exceeds a preset internal
temperature control threshold. Once the thermal
loop control becomes active, the fast charge cur-
rent is initially reduced by a factor of 0.44.
Table 1: Resistor Values.
Enable / Disable
The AAT2550 provides an enable function to con-
trol the charger IC on and off. The enable (EN) pin
is active high. When pulled to a logic low level, the
AAT2550 will be shut down and forced into the
sleep state. Charging will be halted regardless of
the battery voltage or charging state. When the
device is re-enabled, the charge control circuit will
automatically reset and resume charging functions
with the appropriate charging mode based on the
battery charge state and measured cell voltage.
The initial thermal loop current can be estimated by
the following equation:
ITLOOP = ICH · 0.44
The thermal loop control re-evaluates the circuit die
temperature every three seconds and adjusts the
fast charge current back up in small steps to the full
fast charge current level or until an equilibrium cur-
rent is discovered and maximized for the given
ambient temperature condition. The thermal loop
controls the system charge level; therefore, the
AAT2550 will always provide the highest level of
constant current possible in the fast charge mode
for any given ambient temperature condition.
Programming Charge Current
The fast charge constant current charge level is
programmed with a resistor placed between the
ADPSET pin and ground. The accuracy of the fast
charge, as well as the preconditioning trickle
charge current, is dominated by the tolerance of
the set resistor used. For this reason, 1% tolerance
metal film resistors are recommended for the set
resistor function.
Adapter Input Charge Inhibit and Resume
The AAT2550 has an under-voltage lockout and
power on reset feature so that the charger will sus-
pend charging and shut down if the input supply to
the adapter pin drops below the UVLO threshold.
Fast charge constant current levels from 100mA to
1A can be set by selecting the appropriate resistor
value from Table 1. The RSET resistor should be con-
nected between the ADPSET pin and ground.
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AAT2550
Total Power Solution for Portable Applications
ing or un-terminated, as this will cause errors in the
internal timing control circuit.
10000
1000
100
The constant current provided to charge the timing
capacitor is very small, and this pin is susceptible
to noise and changes in capacitance value.
Therefore, the timing capacitor should be physical-
ly located on the printed circuit board layout as
closely as possible to the CT pin. Since the accu-
ADP
10
1
10
100
racy of the internal timer is dominated by the
RSET (kΩ)
capacitance value, 10% tolerance or better ceram-
ic capacitors are recommended. Ceramic capacitor
materials, such as X7R and X5R type, are a good
choice for this application.
Figure 2: IFASTCHARGE vs. RSET
.
Over-Voltage Protection
An over-voltage event is defined as a condition
where the voltage on the BAT pin exceeds the max-
imum battery charge voltage and is set by the over-
voltage protection threshold (VOVP). If an over-volt-
age condition occurs, the AAT2550 charge control
will shut down the device until voltage on the BAT
pin drops below the over-voltage protection thresh-
old (VOVP). The AAT2550 will resume normal charg-
ing operation after the over-voltage condition is
removed. During an over-voltage event, the STAT
LEDs will report a system fault, and the actual fault
condition may be read via the DATA pin signal.
Protection Circuitry
Programmable Watchdog Timer
The AAT2550 contains a watchdog timing circuit for
the adapter input charging mode. Typically, a 0.1µF
ceramic capacitor is connected between the CT pin
and ground. When a 0.1µF ceramic capacitor is
used, the device will time a shutdown condition if
the trickle charge mode exceeds 25 minutes and a
combined trickle charge plus fast charge mode of
three hours. When the device transitions to the con-
stant voltage mode, the timing counter is reset and
will time out after three hours and shut down the
charger (see Table 2).
Over-Temperature Shutdown
The AAT2550 has a thermal protection control cir-
cuit which will shut down charging functions should
the internal die temperature exceed the preset
thermal limit threshold.
Mode
Time
Trickle Charge (TC) Time Out
Trickle Charge (TC) +
Fast Charge (CC) Time Out
Constant Voltage (VC) Mode
Time Out
25 minutes
3 hours
Battery Temperature Fault Monitoring
In the event of a battery over-temperature condi-
tion, the charge control will turn off the internal pass
device and report a battery temperature fault on the
DATA pin function. The STAT LEDs will also display
a system fault. After the system recovers from a
temperature fault, the device will resume charging
operation.
3 hours
Table 2: Summary for a 0.1µF Used for the
Timing Capacitor.
The CT pin is driven by a constant current source
and will provide a linear response to increases in
the timing capacitor value. Thus, if the timing capac-
itor were to be doubled from the nominal 0.1µF
value, the time-out durations would be doubled.
The AAT2550 checks battery temperature before
starting the charge cycle, as well as during all
stages of charging. This is accomplished by moni-
toring the voltage at the TS pin. This system is
intended to use negative temperature coefficient
thermistors (NTC), which are typically integrated
into the battery package. Most of the commonly
If the programmable watchdog timer function is not
needed, it can be disabled by connecting the CT
pin to ground. The CT pin should not be left float-
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Total Power Solution for Portable Applications
used NTC thermistors in battery packs are approx-
imately 10kΩ at room temperature (25°C).
be accomplished by using the STAT1 pin and a sin-
gle LED. Using two LEDs and both STAT pins simply
gives the user more information to the charging
states. Refer to Table 3 for LED display definitions.
The TS pin has been specifically designed to
source 80µA of current to the thermistor. The volt-
age on the TS pin that results from the resistive
load should stay within a window from 330mV to
2.3V. If the battery becomes too hot during charg-
ing due to an internal fault, the thermistor will heat
up and reduce in value, pulling the TS pin voltage
lower than the TS1 threshold, and the AAT2550 will
signal the fault condition.
The LED anodes should be connected to ADP. The
LEDs should be biased with as little current as nec-
essary to create reasonable illumination; therefore,
a ballast resistor should be placed between the
LED cathodes and the STAT1/2 pins. LED current
consumption will add to the overall thermal power
budget for the device package, so it is wise to keep
the LED drive current to a minimum. 2mA should
be sufficient to drive most low-cost green or red
LEDs. It is not recommended to exceed 8mA for
driving an individual status LED.
If the use of the TS pin function is not required by
the system, it should be terminated to ground with
a 10kΩ resistor.
The required ballast resistor value can be estimat-
ed using the following formulas:
Battery Charge Status Indication
The AAT2550 indicates the status of the battery
under charge with two different systems. First, the
device has two status LED driver outputs. These
two LEDs can indicate simple functions such as no
battery charge activity, battery charging, charge
complete, and charge fault. The AAT2550 also pro-
vides a bi-directional data reporting function so that
a system microcontroller can interrogate the DATA
pin and read any one of 13 system states.
For connection to the adapter supply:
VADP - VF(LED)
ILED(STAT1/2)
RB(STAT1/2)
=
Example:
RB(STAT1)
5.5V - 2.0V
2mA
=
= 1.75kΩ
Status Indicator Display
Simple system charging status states can be dis-
played using one or two LEDs in conjunction with the
STAT1 and STAT2 pins on the AAT2550. These two
pins are simple switches to connect the LED cath-
odes to ground. It is not necessary to use both dis-
play LEDs if a user simply wants to have a single
lamp to show "charging" or "not charging." This can
Note: Red LED forward voltage (VF) is typically
2.0V @ 2mA. Green LED forward voltage (VF) is
typically 3.2V @ 2mA.
The four status LED display conditions are
described in Table 3.
Event Description
STAT1
STAT2
Charge Disabled or Low Supply
Charge Enabled Without Battery
Battery Charging
Off
Flash1
On
Off
Flash1
Off
Charge Completed
Off
On
Fault
On
On
Table 3: Status LED Display Conditions.
1. Flashing rate depends on output capacitance.
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AAT2550
Total Power Solution for Portable Applications
and to maintain the integrity of the data timing for
the system, the pull-up resistor on the data line
Digital Charge Status Reporting
The AAT2550 has a comprehensive digital data
reporting system by use of the DATA pin feature.
This function can provide detailed information
regarding the status of the charging system. The
DATA pin is a bi-directional port which will read back
a series of data pulses when the system microcon-
troller asserts a request pulse. This single strobe
request protocol will invoke one of 13 possible return
pulse counts which the microcontroller can look up
based on the serial report table shown in Table 4.
should be low enough in value so that the DATA
signal returns to the high state without delay. If too
small a pull-up resistor is used, the strobe pulse
from the system microcontroller could exceed the
maximum pulse time and the DATA output control
could issue false status reports. A 1.5kΩ resistor is
recommended when pulling the DATA pin high to
5.0V. If the data line is pulled high to a voltage level
less than 5.0V, the pull-up resistor can be calculat-
ed based on a recommended minimum pull-up cur-
rent of 3mA. Use the following formula:
The DATA pin function is active low and should nor-
mally be pulled high to VADP. This data line may
also be pulled high to the same level as the high
state for the logic I/O port on the system microcon-
troller. In order for the DATA pin control circuit to
generate clean, sharp edges for the data output
VPULL-UP
3mA
RPULL-UP
≤
Number
DATA Report Status
1
2
Chip Over-Temperature Shutdown
Battery Temperature Fault
3
Over-Voltage Turn Off
4
Not Used
5
ADP Watchdog Time-Out in Battery Condition Mode
ADP Battery Condition Mode
6
7
ADP Watchdog Time-Out in Constant Current Mode
ADP Thermal Loop Regulation in Constant Current Mode
ADP Constant Current Mode
8
9
10
11
12
23
ADP Watchdog Time-Out in Constant Voltage Mode
ADP Constant Voltage Mode
ADP End of Charging
Data Report Error
Table 4: Serial Data Report Table.
1.8V to 5.0V
IN
RPULL_UP
IN
AAT2550
Status
DATA Pin
Control
GPIO
OUT
OUT
μP GPIO
Port
Figure 3: Data Pin Application Circuit.
20
2550.2006.07.1.0
AAT2550
Total Power Solution for Portable Applications
Data Timing
pulse, the AAT2550 status data control will reply the
The system microcontroller should assert an active
low data request pulse for minimum duration of
200ns; this is specified by the SQPULSE. Upon sens-
ing the rising edge of the end of the data request
data word back to the system microcontroller after a
delay defined by the data report time specification
TDATA(RPT). The period of the following group of data
pulses will be defined by the TDATA specification.
Timing Diagram
SQPULSE
PDATA
SQ
System Reset
System Start
CK
TSYNC
TLAT
TOFF
Data
TDATA(RPT) = TSYNC + TLAT < 2.5 PDATA
TOFF > 2 PDATA
N=3
N=1
N=2
input capacitor in this application will minimize
switching or power bounce effects when the power
supply is "hot plugged."
Capacitor Selection
Input Capacitor
In general, it is good design practice to place a
decoupling capacitor between the ADP pin and
ground. An input capacitor in the range of 1µF to
22µF is recommended. If the source supply is
unregulated, it may be necessary to increase the
capacitance to keep the input voltage above the
under-voltage lockout threshold during device
enable and when battery charging is initiated.
Output Capacitor
The AAT2550 only requires a 1µF ceramic capac-
itor on the BAT pin to maintain circuit stability. This
value should be increased to 10µF or more if the
battery connection is made any distance from the
charger output. If the AAT2550 is to be used in
applications where the battery can be removed
from the charger, such as in the case of desktop
charging cradles, an output capacitor greater than
10µF may be required to prevent the device from
cycling on and off when no battery is present.
If the AAT2550 adapter input is to be used in a sys-
tem with an external power supply source, such as
a typical AC-to-DC wall adapter, then a CIN capaci-
tor in the range of 10µF should be used. A larger
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AAT2550
Total Power Solution for Portable Applications
grammed current source in parallel with the output
capacitor.
Step-Down Converter
Functional Description
The output of the voltage error amplifier programs
the current mode loop for the necessary peak
switch current to force a constant output voltage for
all load and line conditions. Internal loop compen-
sation terminates the transconductance voltage
error amplifier output. For fixed voltage versions,
the error amplifier reference voltage is internally set
to program the converter output voltage. For the
adjustable output, the error amplifier reference is
fixed at 0.6V.
The AAT2550 step-down converter is a high per-
formance 600mA 1.4MHz monolithic power supply.
It has been designed with the goal of minimizing
external component size and optimizing efficiency
over the complete load range. Apart from the small
bypass input capacitor, only a small L-C filter is
required at the output. Typically, a 4.7µH inductor
and a 4.7µF ceramic capacitor are recommended
(see Table 5).
The fixed output version requires only three exter-
nal power components (CIN, COUT, and L). The
adjustable version can be programmed with exter-
nal feedback to any voltage, ranging from 0.6V to
the input voltage. An additional feed-forward
capacitor can also be added to the external feed-
back with a 10µF output capacitor for improved
transient response (see C10 and C11 in Figure 4).
Soft Start / Enable
Soft start limits the current surge seen at the input
and eliminates output voltage overshoot. When
pulled low, the enable input forces the AAT2550
into a low-power, non-switching state. The total
input current during shutdown is less than 1µA.
At dropout, the converter duty cycle increases to
100% and the output voltage tracks the input volt-
age minus the RDS(ON) drop of the P-channel high-
side MOSFET.
Current Limit and Over-Temperature
Protection
For overload conditions, the peak input current is
limited. To minimize power dissipation and stresses
under current limit and short-circuit conditions,
switching is terminated after entering current limit
for a series of pulses. Switching is terminated for
seven consecutive clock cycles after a current limit
has been sensed for a series of four consecutive
clock cycles.
The input voltage range is 2.7V to 5.5V. The con-
verter efficiency has been optimized for all load
conditions, ranging from no load to 600mA.
The internal error amplifier and compensation pro-
vides excellent transient response, load, and line
regulation. Soft start eliminates any output voltage
overshoot when the enable or the input voltage is
applied.
Thermal protection completely disables switching
when internal dissipation becomes excessive. The
junction over-temperature threshold is 140°C with
15°C of hysteresis. Once an over-temperature or
over-current fault conditions is removed, the output
voltage automatically recovers.
Control Loop
The AAT2550 step-down converter is a peak cur-
rent mode control converter. The current through
the P-channel MOSFET (high side) is sensed for
current loop control, as well as short-circuit and
overload protection. A fixed slope compensation
signal is added to the sensed current to maintain
stability for duty cycles greater than 50%. The peak
current mode loop appears as a voltage-pro-
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VIN
input. Under-voltage lockout (UVLO) guarantees
sufficient VIN bias and proper operation of all inter-
nal circuitry prior to activation.
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Configuration
Output Voltage
Inductor
1V, 1.2V
1.5V, 1.8V
2.5V, 3.3V
0.6V to 3.3V
2.2µH
4.7µH
6.8µH
4.7µH
0.6V Adjustable With
External Feedback
Fixed Output
Table 5: Inductor Values.
saturation characteristics. The inductor should not
show any appreciable saturation under normal load
conditions. Some inductors may meet the peak and
average current ratings yet result in excessive loss-
es due to a high DCR. Always consider the losses
associated with the DCR and its effect on the total
converter efficiency when selecting an inductor.
Step-Down Converter
Applications Information
Inductor Selection
The step-down converter uses peak current mode
control with slope compensation to maintain stability
for duty cycles greater than 50%. The output induc-
tor value must be selected so the inductor current
down slope meets the internal slope compensation
requirements. The internal slope compensation for
the adjustable and low-voltage fixed versions of the
AAT2550 is 0.24A/µsec. This equates to a slope
compensation that is 75% of the inductor current
down slope for a 1.5V output and 4.7µH inductor.
The Sumida 4.7µH CDRH3D16 series inductor has
a 105mΩ DCR and a 900mA DC current rating. At
full load, the inductor DC loss is 38mW, which gives
a 4% loss in efficiency for a 600mA, 1.5V output.
Input Capacitor
Select a 4.7µF to 10µF X7R or X5R ceramic capac-
itor for the input. To estimate the required input
capacitor size, determine the acceptable input rip-
ple level (VPP) and solve for C. The calculated
value varies with input voltage and is a maximum
when VIN is double the output voltage.
0.75 ⋅ VO 0.75 ⋅ 1.5V
= 0.24
A
m =
=
L
4.7μH
μsec
This is the internal slope compensation for the
adjustable (0.6V) version or low-voltage fixed ver-
sions. When externally programming the 0.6V ver-
sion to 2.5V, the calculated inductance is 7.5µH.
VO
VIN
⎛
· 1
⎝
VO
VIN
⎞
⎠
-
CIN =
⎛
⎝
VPP
IO
⎞
⎠
- ESR
·
FS
0.75 ⋅ VO
0.75
⋅
VO
A
μsec
A
L =
=
≈
3
⋅ VO
m
VO
VIN
⎛
VO
VIN
⎞
⎠
1
4
0.24A
· 1
-
=
for VIN = 2 · VO
μsec
⎝
μsec
A
= 3
⋅ 2.5V = 7.5μH
1
CIN(MIN)
=
⎛
⎝
VPP
IO
⎞
⎠
- ESR
·
4
·
FS
In this case, a standard 6.8µH value is selected.
For high-voltage fixed versions (≥2.5V), m = 0.48A/
µsec. Table 5 displays inductor values for the
AAT2550 fixed and adjustable options.
Always examine the ceramic capacitor DC voltage
coefficient characteristics when selecting the prop-
er value. For example, the capacitance of a 10µF,
6.3V, X5R ceramic capacitor with 5.0V DC applied
is actually about 6µF.
Manufacturer's specifications list both the inductor
DC current rating, which is a thermal limitation, and
the peak current rating, which is determined by the
2550.2006.07.1.0
23
AAT2550
Total Power Solution for Portable Applications
The maximum input capacitor RMS current is:
Since the inductance of a short PCB trace feeding
the input voltage is significantly lower than the
power leads from the bench power supply, most
applications do not exhibit this problem.
VO
VIN
⎛
· 1
⎝
VO
VIN
⎞
⎠
IRMS = IO
·
-
In applications where the input power source lead
inductance cannot be reduced to a level that does
not affect the converter performance, a high ESR
tantalum or aluminum electrolytic input capacitor
should be placed in parallel with the low ESR
bypass ceramic input capacitor (C6 of Figure 4).
This dampens the high Q network and stabilizes
the system.
The input capacitor RMS ripple current varies with
the input and output voltage and will always be less
than or equal to half of the total DC load current.
VO
VIN
⎛
· 1
⎝
VO
VIN
⎞
⎠
1
2
-
=
D
· (1 - D) = 0.52 =
Output Capacitor
for VIN = 2 · VO
The output capacitor limits the output ripple and
provides holdup during large load transitions. A
4.7µF to 10µF X5R or X7R ceramic capacitor typi-
cally provides sufficient bulk capacitance to stabi-
lize the output during large load transitions and has
the ESR and ESL characteristics necessary for low
output ripple.
IO
IRMS(MAX)
=
2
VO
·
VIN
⎛
⎝
VO
VIN
⎞
⎠
1
-
The term
appears in both the input
The output voltage droop due to a load transient is
dominated by the capacitance of the ceramic out-
put capacitor. During a step increase in load cur-
rent, the ceramic output capacitor alone supplies
the load current until the loop responds. Within two
or three switching cycles, the loop responds and
the inductor current increases to match the load
current demand. The relationship of the output volt-
age droop during the three switching cycles to the
output capacitance can be estimated by:
voltage ripple and input capacitor RMS current
equations and is a maximum when VO is twice VIN.
This is why the input voltage ripple and the input
capacitor RMS current ripple are a maximum at
50% duty cycle.
The input capacitor provides a low impedance loop
for the edges of pulsed current drawn by the
AAT2550. Low ESR/ESL X7R and X5R ceramic
capacitors are ideal for this function. To minimize
stray inductance, the capacitor should be placed as
closely as possible to the IC. This keeps the high
frequency content of the input current localized,
minimizing EMI and input voltage ripple.
3
·
VDROOP FS
ΔILOAD
COUT
=
·
Proper placement of the input capacitors (C4 and
C5) can be seen in the evaluation board schemat-
ic in Figure 4.
Once the average inductor current increases to the
DC load level, the output voltage recovers. The
above equation establishes a limit on the minimum
value for the output capacitor with respect to load
transients.
A laboratory test set-up typically consists of two
long wires running from the bench power supply to
the evaluation board input voltage pins. The induc-
tance of these wires, along with the low-ESR
ceramic input capacitor, can create a high Q net-
work that may affect converter performance. This
problem often becomes apparent in the form of
excessive ringing in the output voltage during load
transients. Errors in the loop phase and gain
measurements can also result.
The internal voltage loop compensation also limits
the minimum output capacitor value to 4.7µF. This
is due to its effect on the loop crossover frequency
(bandwidth), phase margin, and gain margin.
Increased output capacitance will reduce the
crossover frequency with greater phase margin.
24
2550.2006.07.1.0
AAT2550
Total Power Solution for Portable Applications
The maximum output capacitor RMS ripple current
is given by:
V
V
1.5V
0.6V
⎛
⎝
⎞
⎛
⎝
⎞
- 1 ·
R8 =
OUT -1
·
R7 =
59kΩ = 88.5kΩ
⎠
⎠
REF
1
V
OUT · (VIN(MAX) - VOUT
FS VIN(MAX)
)
The adjustable version of the AAT2550, combined
with an external feedforward capacitor (C10 and
C11 in Figure 4), delivers enhanced transient
response for extreme pulsed load applications. The
addition of the feedforward capacitor typically
requires a larger output capacitor for stability.
IRMS(MAX)
=
·
L
·
·
2 · 3
Dissipation due to the RMS current in the ceramic
output capacitor ESR is typically minimal, resulting in
less than a few degrees rise in hot-spot temperature.
Thermal Considerations
Adjustable Output Resistor Selection
The AAT2550 is available in a 4x4mm QFN pack-
age, which has a typical thermal resistance of
28°C/W when the exposed paddle is soldered to a
printed circuit board (PCB) in the manner dis-
cussed in the Printed Circuit Board Layout section
of this datasheet. Thermal resistance will vary with
the PCB area, ground plane area, size and number
of other adjacent components, and the heat they
generate. The maximum ambient operating tem-
perature is limited by either the design derating cri-
teria, the over-temperature shutdown temperature,
or the thermal loop charge current reduction con-
trol. To calculate the junction temperature, sum the
step-down converter losses with the battery charg-
er losses. Multiply the total losses by the package
thermal resistance and add to the ambient temper-
ature to determine the junction temperature rise.
For applications requiring an adjustable output volt-
age, the 0.6V version can be externally pro-
grammed. Resistors R7 through R10 of Figure 4 pro-
gram the output to regulate at a voltage higher than
0.6V. To limit the bias current required for the exter-
nal feedback resistor string while maintaining good
noise immunity, the minimum suggested value for
R7 and R9 is 59kΩ. Although a larger value will fur-
ther reduce quiescent current, it will also increase
the impedance of the feedback node, making it more
sensitive to external noise and interference. Table 6
summarizes the resistor values for various output
voltages with R7 and R9 set to either 59kΩ for good
noise immunity or 221kΩ for reduced no load input
current.
R7, R9 = 59kΩ R7, R9 = 221kΩ
VOUT (V)
R8, R10 (kΩ)
R8, R10 (kΩ)
TJ(MAX) = (PSD + PC) · θJA + TAMB
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
3.3
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
75
113
150
187
221
261
301
332
442
464
523
715
1000
PSD is the total loss associated with both step-down
converters and PC is the loss associated with the
charger. The total losses will vary considerably
depending on input voltage, load, and charging
current. While charging a battery, the current capa-
bility of the step-down converters is limited.
124
137
187
267
Table 6: Adjustable Resistor Values for Use
With 0.6V Step-Down Converter.
2550.2006.07.1.0
25
AAT2550
Total Power Solution for Portable Applications
(tSW · FS), conduction losses (I2 · RDS(ON)), and qui-
escent current losses (IQ · VIN). At full load, assum-
ing continuous conduction mode, a simplified form
of the step-down converter losses is:
Step-Down Converter Losses
There are three types of losses are associated with
the AAT2550 step-down converter: switching losses
2
2
IOA
·
(RDS(ON)H · VOA
+
RDS(ON)L · (VIN - VOA)) + IOB
VIN
· (RDS(ON)H · VOB + RDS(ON)L · (VIN - VOB))
PSD
=
+ (tSW · FS · (IOA + IOB) + 2 · IQ ) · VIN
For the condition where one channel is in dropout
at 100% duty cycle (IOA), the step-down converter
dissipation is:
PC = Total Charger Dissipation
VADP = Adapter Voltage
VMIN = Preconditioning Voltage Threshold
ICH = Programmed Charge Current
2
PSD
=
+
IOA
·
RDS(ON)H
IQC = Charger Quiescent Current Consumed by
the Charger
2
IOB
·
(RDS(ON)H · VOB
+ RDS(ON)L · (VIN - VOB))
VIN
For an application where no load is applied to the
step-down converters and the charger current is
set to 1A with VADP = 5.0V, the maximum charger
dissipation occurs at the preconditioning voltage
+ (tSW · FS · IOB + 2 · IQ ) · VIN
threshold VMIN
.
PSD
VIN
= Step-Down Converter Dissipation
= Converter Input Voltage
RDS(ON)H = High Side MOSFET On Resistance
RDS(ON)L = Low Side MOSFET On Resistance
PC = (VADP - VMIN) · ICH + VADP · IQC
= (5.0V - 3.0V) · 1A + 5.0V · 0.74mA
= 2W
VOA
VOB
IOA
IOB
IQ
= Converter A Output Voltage
= Converter B Output Voltage
= Converter A Load Current
= Converter B Load Current
= Converter Quiescent Current
= Switching Time Estimate
The charger thermal loop begins reducing the
charge current at a 110°C junction temperature
(TLOOP_IN). The ambient temperature at which the
charger thermal loop begins reducing the charge
current is:
tSW
FS
= Converter Switching Frequency
Always use the RDS(ON) and quiescent current
value that corresponds to the applied input voltage.
TA = TLOOP_IN - θJA · PC
Battery Charger Losses
= 110°C - (28°C/W) · 2W
= 54°C
The maximum battery charger loss is:
PC = (VADP - VMIN) · ICH + VADP · IQC
Therefore, under the given conditions, the
AAT2550 battery charger will enter the thermal
loop charge current reduction at an ambient tem-
perature greater than 54°C.
26
2550.2006.07.1.0
AAT2550
Total Power Solution for Portable Applications
Conditions:
Total Power Loss Examples
The most likely high power scenario is when the
charger and step-down converter are both opera-
tional and powered from the adapter. To examine
the step-down converter maximum current capabil-
ity for this condition, it is necessary to determine
the step-down converter MOSFET RDS(ON), quies-
cent current, and switching losses at the adapter
voltage level (5V). This example shows that with a
600mA battery charge current, the buck converter
output current capability is limited 400mA. This lim-
its the junction temperature to 110°C and avoids
the thermal loop charge reduction at a 70°C ambi-
ent temperature.
VOA
VOB
IQ
2.5V @
400mA
1.8V @
400mA
70µA
Step-Down Converter A
Step-Down Converter B
Converter Quiescent
Current
VIN
=
5.0V
3.0V
Charger and Step-Down
Converter Input Voltage
Battery Preconditioning
Threshold Voltage
VADP
VMIN
ICH
IOP
0.6A
Battery Charge Current
Charger Operating Current
0.75mA
2
2
IOA
·
(RDS(ON)H · VOA
+
RDS(ON)L · (VIN - VOA)) + IOB
VIN
· (RDS(ON)H · VOB + RDS(ON)L · (VIN - VOB))
PTOTAL
=
=
+ ( SW
t
· FS · (IOA
+ IOB) + 2 · IQ) · VIN + (VADP - VMIN) · ICH + VADP · IOP
0.4A2
·
(0.475Ω · 2.5V
+
0.45Ω · (5.0V - 2.5V)) + 0.4A2
5.0V
·
(0.475Ω · 1.8V
+
0.45Ω · (5.0V - 1.8V))
+ 2 · (5ns · 1.4MHz · 0.4A + 70µA) · 5.0V + (5.0V - 3.0V) · 0.6A + 5.0V · 0.75mA = 1.38W
TJ(MAX) = TAMB + θJA · PLOSS
= 70°C + (28°C/W) · 1.38W
= 108°C
The step-down converter load current capability is
greatest when the battery charger is disabled. The
following example demonstrates the junction tem-
perature rise for conditions where the battery charg-
er is disabled and full load is applied to both con-
verter outputs at the nominal battery input voltage.
Conditions:
VO1
2.5V @
600mA
1.8V @
600mA
70µA
Step-Down Converter A
Step-Down Converter B
VO2
IQ
Converter Quiescent
Current
VIN
3.6V
0A
Charger and Step-Down
Converter Input Voltage
Charger Disabled
ICH
=
IOP
2550.2006.07.1.0
27
AAT2550
Total Power Solution for Portable Applications
2
2
IOA
·
(RDS(ON)H · VOA
+
RDS(ON)L · (VIN - VOA)) + IOB
VIN
· (RDS(ON)H · VOB + RDS(ON)L · (VIN - VOB))
PTOTAL
=
=
+ ( SW
t
· FS · (IOA
+ IOB) + 2 ·
I
Q) · VIN + (VADP - VMIN) · ICH + VADP · IOP
0.6A2
·
(0.58Ω · 2.5V
+
0.56Ω · (3.6V - 2.5V)) + 0.2A2
3.6V
·
(0.58Ω · 1.8V
+
0.56Ω · (3.6V - 1.8V))
+ 2 · (5ns · 1.4MHz · 0.4A + 70µA) · 3.6V = 0.443W
TJ(MAX) = TAMB + θJA · PLOSS
= 85°C + (28°C/W) · 0.443W
= 97°C
4. The resistance of the trace from the load return
to GND should be kept to a minimum. This min-
imizes any error in DC regulation due to differ-
ences in the potential of the internal signal
ground and the power ground.
Printed Circuit Board Layout
Use the following guidelines to ensure a proper
printed circuit board layout.
1. Step-down converter bypass capacitors (C4
and C5 in Figure 4) must be placed as close as
possible to the step-down converter inputs.
5. For good thermal coupling, vias are required
from the pad for the QFN paddle to the ground
plane. Via diameters should be 0.3mm to
0.33mm and positioned on a 1.2mm grid. Avoid
close placement to other heat generating
devices.
2. The connections from the LXA and LXB pins of
the step-down converters to the output induc-
tors should be kept as short as possible. This
is a switching node, so minimizing the length
will reduce the potential of this noisy trace
interfering with other high impedance noise
sensitive nodes.
6. Minimize the trace impedance from the battery
to the BAT pin. The charger output is not
remotely sensed, so any drop in the output
across the BAT output trace feeding the battery
will add to the error in the EOC battery voltage.
To minimize voltage drops on the PCB, main-
tain an adequate high current carrying trace
width.
3. The feedback trace should be separate from
any power trace and connected as closely as
possible to the load point. Sensing along a high
current load trace will degrade the DC load reg-
ulation. If external feedback resistors are used,
they should be placed as closely as possible to
the FB pin. This prevents noise from being cou-
pled into the high impedance feedback node.
28
2550.2006.07.1.0
AAT2550
Total Power Solution for Portable Applications
J1
J8
C6
GND GND
100µF
TB1
J2
GND
3
2
1
C4
R9
R7
C5
J3
VIN
10µF 59.0k
59.0k
10µF
VOB
TB2
1
2
3
VOA
J4
LXB
C11
n/a
R8
267k
R10
118k
C10
n/a
J5
L1 6.8µH
1
18
VOB
ENA
LXB
L2 4.7µH
VOA
C9
4.7µF
2
17
16
15
14
13
LXA
PGND
CT
C8
4.7µF
LXA
3
U1
AAT2550
J7
CT
PGND
DATA
N/C
4
5
6
C12
0.1µF
STAT1
STAT2
TS
SW1
Data Strobe
R1
4.7k
ADPSET
R2
R3
1k
4.7k
D1
C14
R6
STAT1
Red
0.01µF
8.06k
D2
STAT2
Green
TB3
ADP
GND
1
2
C3
10µF
TB4
Adapter Input
1
2
3
1
2
3
BAT
GND
TS
Charger Enable
TB5
Battery
R4
10k
Figure 4: AAT2550 Evaluation Board Schematic.
2550.2006.07.1.0
29
AAT2550
Total Power Solution for Portable Applications
Figure 5: AAT2550 Evaluation Board
Top Side Layout.
Figure 6: AAT2550 Evaluation Board
Bottom Side Layout.
Reference
Designator Manufacturer
Qty. Description
Part Number
1
1
3
Conn. Term Block 2.54mm 2 POS
Conn. Term Block 2.54mm 3 POS
Ceramic Capacitor 10µF 10%, 10V,
X5R, 0805
Adapter Input Phoenix Contact
Battery Output Phoenix Contact
C3,C4,C5
C8,C9
C12
Murata
Murata
Vishay
2
1
Ceramic Capacitor 4.7µF 10%, 6.3V,
X5R, 0805
Ceramic Capacitor 0.1µF 25V 10%
X5R 0603
1
2
2
2
1
1
2
1
1
1
1
1
1
1
Tantalum Capacitor 100µF, 6.3V, Case C
C6
Vishay
Vishay
Sumida
Vishay
Vishay
Vishay
Vishay
Vishay
Vishay
Vishay
Optional Ceramic Capacitor 100pF, 0402, COG C10, C11
Ferrite Shielded Inductor CDRH3D16
4.7k, 5%, 1/16W, 0402
1.0k, 5%, 1/16W, 0402
8.06k, 1%, 1/16W, 0402
59.0k, 1%, 1/16W, 0402
1%, 1/16W, 0402
L1, L2
R1,R2
R3
R6
R7,R9
R10
R8
1%, 1/16W, 0402
10k, 5%, 1/16W, 0402
Red LED, 1206
R4
D1
Chicago Miniature Lamp CMD15-21SRC/TR8
Chicago Miniature Lamp CMD15-21SRC/TR8
Green LED, 1206
D2
Switch Tact 6mm SPST H = 5.0mm
AAT2550 Total Power Solution for Portable
Applications
SW1
U1
ITT Industries/C&K Div
Advanced Analogic
Technologies
CKN9012-ND
AAT2550ISK-CAA-T1
Table 7: AAT2550 Evaluation Board Bill of Materials.
30
2550.2006.07.1.0
AAT2550
Total Power Solution for Portable Applications
Inductance
(µH)
Max DC
Current (A)
DCR
Size (mm)
LxWxH
Ω
Manufacturer
Part Number
( )
Type
Sumida
CDRH3D16-2R2
CDRH3D16-4R7
CDRH3D16-6R8
LQH2MCN4R7M02
LQH32CN4R7M23
LPO3310-472
2.2
4.7
6.8
4.7
4.7
4.7
4.7
6.8
4.7
1.20
0.90
0.73
0.40
0.45
0.80
0.98
0.82
1.30
0.072
0.105
0.170
0.80
3.8x3.8x1.8
3.8x3.8x1.8
3.8x3.8x1.8
2.0x1.6x0.95
2.5x3.2x2.0
3.2x3.2x1.0
3.1x3.1x1.85
3.1x3.1x1.85
5.7x4.4x1.0
Shielded
Shielded
Sumida
Sumida
Shielded
MuRata
Non-Shielded
Non-Shielded
1mm
MuRata
0.20
Coilcraft
Coiltronics
Coiltronics
Coiltronics
0.27
SD3118-4R7
0.122
0.175
0.122
Shielded
SD3118-6R8
Shielded
SDRC10-4R7
1mm Shielded
Table 8: Typical Surface Mount Inductors.
Manufacturer
Part Number
Value
Voltage
Temp. Co.
Case
MuRata
MuRata
MuRata
GRM219R61A475KE19
GRM21BR60J106KE19
GRM21BR60J226ME39
4.7µF
10µF
22µF
10V
6.3V
6.3V
X5R
X5R
X5R
0805
0805
0805
Table 9: Surface Mount Capacitors.
Adjustable Version
(0.6V device)
VOUT (V)
1
R7, R9 = 59kΩ
R8, R10 (kΩ)
R7, R9 = 221kΩ
R8, R10 (kΩ)
L1, L2 (µH)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
3.3
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
75.0
113
150
187
221
261
301
332
442
464
523
715
1000
2.2
2.2
2.2
2.2
2.2
2.2
4.7
4.7
4.7
4.7
6.8
6.8
6.8
124
137
187
267
Fixed Version
VOUT (V)
R7, R9 Not Used
R8, R10 (kΩ)
L1, L2 (µH)
0.6-3.3V
0
4.7
Table 10: Evaluation Board Component Values.
1. For reduced quiescent current, R7 and R9 = 221kΩ.
2550.2006.07.1.0
31
AAT2550
Total Power Solution for Portable Applications
Step-Down Converter Design Example
Specifications
VO1 = 2.5V @ 400mA (adjustable using 0.6V version), pulsed load ΔILOAD = 300mA
VO2 = 1.8V @ 400mA (adjustable using 0.6V version), pulsed load ΔILOAD = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
FS = 1.4MHz
TAMB = 85°C
2.5V VO1 Output Inductor
μsec
A
μsec
A
(see Table 5)
L1 = 3
⋅ VO1 = 3
⋅ 2.5V = 7.5μH
For Sumida inductor CDRH3D16, 6.8µH, DCR = 170mΩ.
⎛
⎞
2.5V
⎠
4.2V
VO
L1 ⋅ FS
VO1
2.5
V
⎛
⎞
ΔI1 =
⋅ 1 -
⎝
=
⋅ 1 -
= 106mA
⎝
VIN
6.8μH ⋅ 1.4MHz
⎠
ΔI1
2
IPK1 = IO1
+
= 0.4A + 0.053A = 0.453A
PL1 = IO12 ⋅ DCR = 0.452 ⋅ 170mΩ = 0.452A2 ⋅ 170mΩ = 34mW
1.8V VO2 Output Inductor
μsec
A
μsec
A
(see Table 5)
⋅ 1.8V = 5.4μH
L2 = 3
⋅ VO2 = 3
For Sumida inductor CDRH3D16, 4.7µH, DCR = 105mΩ.
⎛
⎞
⎠
VO2
L ⋅ FS
VO2
VIN
⎠
1.8
V
1.8V
4.2V
⎛
⎞
ΔI2 =
⋅ 1 -
⎝
=
⋅ 1 -
= 156mA
⎝
4.7μH ⋅ 1.4MHz
ΔI2
2
IPK2 = IO2
+
= 0.4A + 0.078A = 0.48A
PL2 = IO22 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
32
2550.2006.07.1.0
AAT2550
Total Power Solution for Portable Applications
2.5V Output Capacitor
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
0.2V · 1.4MHz
COUT
=
=
= 3.2μF
(VOUT) · (VIN(MAX) - VOUT
)
1
2.5V · (4.2V - 2.5V)
1
·
= 21mArms
IRMS(MAX)
=
·
=
10μH · 1.4MHz · 4.2V
L · FS · VIN(MAX)
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (21mA)2 = 2.2μW
1.8V Output Capacitor
3 · ΔILOAD
VDROOP · FS
3 · 0.3A
COUT
=
=
= 3.2μF
0.2V · 1.4MHz
(VOUT) · (VIN(MAX) - VOUT
)
1
1.8V · (4.2V - 1.8V)
1
·
= 45mArms
IRMS(MAX)
=
·
=
4.7μH · 1.4MHz · 4.2V
L · FS · VIN(MAX)
2· 3
2· 3
Pesr = esr · IRMS2 = 5mΩ · (45mA)2 = 10μW
Input Capacitor
Input Ripple VPP = 25mV.
1
1
CIN =
=
= 6.8μF
⎛
⎝
VPP
⎞
⎠
⎛
⎝
25mV
0.8A
⎞
- ESR
·
4
·
FS
- 5mΩ
·
4
·
1.4MHz
IO1
+
IO2
⎠
IO1 + IO2
2
IRMS(MAX)
P = esr
=
·
= 0.4Arms
IRMS2 = 5mΩ
·
(0.4A)2 = 0.8mW
2550.2006.07.1.0
33
AAT2550
Total Power Solution for Portable Applications
Ordering Information
Voltage
Package
Converter 1
Converter 2
Marking1
Part Number (Tape and Reel)2
AAT2550ISK-CAA-T1
QFN44-24
0.6V
0.6V
RJXYY
All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means
semiconductor products that are in compliance with current RoHS standards, including
the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more
information, please visit our website at http://www.analogictech.com/pbfree.
Legend
Voltage
Code
Adjustable
(0.6V)
0.9
A
B
E
G
I
1.2
1.5
1.8
1.9
Y
N
O
P
Q
R
S
T
2.5
2.6
2.7
2.8
2.85
2.9
3.0
3.3
W
C
4.2
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
34
2550.2006.07.1.0
AAT2550
Total Power Solution for Portable Applications
QFN44-24
Pin 1 Identification
0.305 0.075
Pin 1 Dot By Marking
19
24
18
1
R0.030Max
13
6
12
7
4.000 0.050
2.7 0.05
Top View
Bottom View
0.214 0.036
Side View
All dimensions in millimeters.
© Advanced Analogic Technologies, Inc.
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or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice.
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AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are regis-
tered trademarks or trademarks of their respective holders.
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830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
2550.2006.07.1.0
35
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