LTC4081EDD-PBF [Linear]
500mA Li-Ion Charger with NTC Input and 300mA Synchronous Buck; 500毫安锂离子电池充电器与NTC输入和300毫安同步降压
| 型号： | LTC4081EDD-PBF |
| 厂家： | 
Linear |
| 描述： | 500mA Li-Ion Charger with NTC Input and 300mA Synchronous Buck |
| 文件： | 总24页 (文件大小：282K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC4081
500mA Li-Ion Charger
with NTC Input and
300mA Synchronous Buck
U
DESCRIPTIO
FEATURES
Battery Charger:
The LTC4081 is a complete constant-current/constant-
voltage linear battery charger for a single-cell 4.2V
lithium-ion/polymer battery with an integrated 300mA
synchronous buck converter. A 3mm × 3mm DFN pack-
age and low external component count make the LTC4081
especially suitable for portable applications. Furthermore,
the LTC4081 is specifically designed to work within USB
power specifications.
■
Constant-Current/Constant-Voltage Operation
with Thermal Feedback to Maximize Charge Rate
Without Risk of Overheating
■
Internal 4.5 Hour Safety Timer for Termination
■
Charge Current Programmable Up to 500mA with
5% Accuracy
■
NTC Thermistor Input for Temperature Qualified
Charging
The CHRG pin indicates when charge current has
dropped to ten percent of its programmed value (C/10).
An internal 4.5 hour timer terminates the charge cycle.
The full-featured LTC4081 battery charger also includes
tricklecharge,automaticrecharge,soft-start(tolimitinrush
current) and an NTC thermistor input used to monitor
battery temperature.
■
C/10 Charge Current Detection Output
■
5μA Supply Current in Shutdown Mode
Switching Regulator:
■
High Efficiency Synchronous Buck Converter
■
300mA Output Current (Constant-Frequency Mode)
■
2.7V to 4.5V Input Range (Powered from BAT Pin)
■
0.8V to V Output Range
BAT
■
The LTC4081 integrates a synchronous buck converter
that is powered from the BAT pin. It has an adjustable
output voltage and can deliver up to 300mA of load cur-
rent. The buck converter also features low-current high-
efficiency Burst Mode operation that can be selected by
the MODE pin.
MODEPinSelectsFixed(2.25MHz)Constant-Frequency
PWM Mode or Low I (23μA) Burst Mode® Operation
CC
■
■
2μA BAT Current in Shutdown Mode
10-lead, low profile (0.75 mm) 3mm × 3mm DFN
package
U
APPLICATIO S
The LTC4081 is available in a 10-lead, low profile (0.75
mm) 3mm × 3mm DFN package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents,
including 6522118.
■
Wireless Headsets
■
Bluetooth Applications
■
Portable MP3 Players
Multifunction Wristwatches
■
U
Buck Efficiency vs Load Current
(VOUT = 1.8V)
TYPICAL APPLICATIO
100
80
60
40
20
0
1000
100
10
Li-Ion Battery Charger with 1.8V Buck Regulator
EFFICIENCY
(Burst)
510Ω
EFFICIENCY
(PWM)
POWER
LOSS
V
CC
(3.75V
TO 5.5V)
V
CHRG
BAT
CC
500mA
(PWM)
EN_BUCK
LTC4081
4.2V
100k
+
1
Li-Ion/
4.7μF
POWER LOSS
1OμH
POLYMER
BATTERY
(Burst)
NTC
SW
FB
V
V
= 3.8V
= 1.8V
BAT
OUT
0.1
0.01
4.7μF
10pF
1M
EN_CHRG
L = 10μH
C = 4.7μF
V
OUT
(1.8V/300mA)
MODE GND PROG
100k
T
0.01
0.1
1
10
100
1000
806Ω
806k
4.7μF
LOAD CURRENT (mA)
4081 TA01b
4081 TA01a
4081f
1
LTC4081
W W U W
ABSOLUTE AXI U RATI GS
(Note 1)
BAT Short-Circuit Duration............................Continuous
BAT Pin Current ...................................................800mA
PROG Pin Current....................................................2mA
Junction Temperature ...........................................125°C
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range.................. – 65°C to 125°C
V , t < 1ms and Duty Cycle < 1%.............. – 0.3V to 7V
CC
CC
V
Steady State......................................... – 0.3V to 6V
BAT, CHRG.................................................. – 0.3V to 6V
EN_CHRG, PROG, NTC ...................– 0.3V to V + 0.3V
CC
MODE, EN_BUCK.......................... – 0.3V to V + 0.3V
BAT
FB ............................................................... – 0.3V to 2V
PIN CONFIGURATION
TOP VIEW
BAT
1
2
3
4
5
10 SW
V
CC
9
8
7
6
EN_BUCK
11
EN_CHRG
PROG
MODE
FB
NTC
CHRG
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
T
= 110°C, θ = 43°C/W (NOTE 3)
JA
JMAX
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4081EDD#PBF
LTC4081EDD#TRPBF
LDBX
10-Lead (3mm × 3mm) DFN
0°C to 70°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating tempera-
ture range, otherwise specifications are at TA = 25°C, VCC = 5V, VBAT = 3.8V, VEN_CHRG = 0V, VNTC = 0V, VEN_BUCK = VBAT, VMODE = 0V.
(Note 2)
SYMBOL
PARAMETER
CONDITIONS
(Note 4)
MIN
3.75
2.7
TYP
5
MAX
5.5
UNITS
●
●
V
Battery Charger Supply Voltage
V
V
CC
V
BAT
Input Voltage for the Switching
Regulator
(Note 5)
3.8
4.5
●
●
I
I
Quiescent Supply Current (Charger On,
Switching Regulator Off)
V
V
= 4.5V (Forces I and I = 0),
PROG
EN_BUCK
110
300
10
μA
CC
BAT
BAT
= 0
Supply Current in Shutdown (Both
Battery Charger and Switching
Regulator Off)
V
V
V
= 5V, V
= 4V, V
= 0, V > V
BAT
5
2
μA
μA
CC_SD
EN_CHRG
EN_CHRG
BAT
EN_BUCK
EN_BUCK
CC
= 0, V (3.5V) <
CC
(4V)
4081f
2
LTC4081
ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating tempera-
ture range, otherwise specifications are at TA = 25°C, VCC = 5V, VBAT = 3.8V, VEN_CHRG = 0V, VNTC = 0V, VEN_BUCK = VBAT, VMODE = 0V.
(Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
●
I
Battery Current in Shutdown (Both
Battery Charger and Switching
Regulator Off)
V
V
V
= 5V, V
= 4V, V
= 0, V > V
BAT
0.6
2
5
μA
μA
BAT_SD
EN_CHRG
EN_CHRG
BAT
EN_BUCK
EN_BUCK
CC
= 0, V (3.5V) <
CC
(4V)
Battery Charger
V
FLOAT
V
BAT
Regulated Output Voltage
I
I
= 2mA
4.179
4.158
4.2
4.2
4.221
4.242
V
V
BAT
BAT
= 2mA, 4.3V < V < 5.5V
●
CC
●
●
I
Current Mode Charge Current
Undervoltage Lockout Voltage
R
R
= 4k; Current Mode; V
= 0
EN_BUCK
90
100
500
110
525
mA
mA
BAT
PROG
PROG
EN_BUCK
= 0.8k; Current Mode; V
= 0
475
●
●
V
V
CC
V
CC
V
CC
Rising
Falling
3.5
2.8
3.6
3.0
3.7
3.2
V
V
UVLO_CHRG
PROG
●
V
PROG Pin Servo Voltage
0.8k ≤ R
≤ 4k
0.98
1.0
1.02
V
PROG
V
ASD
Automatic Shutdown Threshold Voltage (V – V ), V Low to High
60
15
82
32
100
45
mV
mV
CC
BAT
CC
(V – V ), V High to Low
CC
BAT
CC
t
I
Battery Charger Soft-Start Time
Trickle Charge Current
180
50
μs
mA
V
SS_CHRG
TRKL
V
V
= 2V, R
Rising
= 0.8k
35
65
BAT
PROG
●
V
V
Trickle Charge Threshold Voltage
2.75
100
2.9
150
3.05
350
TRKL
BAT
Trickle Charge Threshold Voltage
Hysteresis
mV
TRHYS
ΔV
Recharge Battery Threshold Voltage
V
FLOAT
– V , 0°C < T < 85°C
70
100
130
mV
RECHRG
BAT
A
ΔV
ΔV
(V – V ) Undervoltage Current
I
I
= 0.9 I
180
90
300
130
mV
mV
UVCL1,
UVCL2
CC
BAT
BAT
BAT
CHG
CHG
Limit Threshold Voltage
Charge Termination Timer
Recharge Time
= 0.1 I
●
●
●
●
t
3
4.5
2.25
1.125
0.1
6
3
hrs
hrs
TIMER
1.5
Low-Battery Charge Time
End of Charge Indication Current Level
V
= 2.5V
0.75
0.085
1.5
0.115
hrs
BAT
I
R
= 2k (Note 6)
mA/mA
°C
C/10
PROG
T
Junction Temperature in Constant-
Temperature Mode
115
LIM
R
Power FET On-Resistance (Between
CC
I
= 350mA, V = 4V
700
2
mΩ
Hz
ON_CHRG
BADBAT
BAT
CC
V
and BAT)
f
Defective Battery Detection CHRG Pulse V = 2V
Frequency
BAT
D
Defective Battery Detection CHRG Pulse V = 2V
75
%
BADBAT
BAT
Frequency Duty Ratio
I
NTC Pin Current
V
NTC
= 2.5V
1
μA
NTC
V
V
V
Cold Temperature Fault Threshold
Voltage
Rising Voltage Threshold
Hysteresis
0.76 • V
V
V
COLD
HOT
DIS
CC
0.015 • V
CC
Hot Temperature Fault Threshold
Voltage
Falling Voltage Threshold
Hysteresis
0.35 • V
V
V
CC
0.017 • V
CC
NTC Disable Threshold Voltage
Falling Threshold; V = 5V
82
50
mV
mV
CC
Hysteresis
f
Fault Temperature CHRG Pulse
Frequency
2
Hz
NTC
D
NTC
Fault Temperature CHRG Pulse
Frequency Duty Ratio
25
%
4081f
3
LTC4081
ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating tempera-
ture range, otherwise specifications are at TA = 25°C, VCC = 5V, VBAT = 3.8V, VEN_CHRG = 0V, VNTC = 0V, VEN_BUCK = VBAT, VMODE = 0V.
(Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Buck Converter
●
●
V
FB Servo Voltage
0.78
–50
1.8
0.80
0.82
50
V
nA
FB
I
f
I
FB Pin Input Current
Switching Frequency
V
= 0.85V
FB
FB
2.25
1.9
2.75
MHz
mA
OSC
No-Load Battery Current (Continuous
Frequency Mode)
No-Load for Regulator, V
L = 10μH, C = 4.7μF
= 5V,
= 5V,
BAT_NL_CF
EN_CHRG
I
I
No-Load Battery Current (Burst Mode
Operation)
No-Load for Regulator, V
MODE = V , L = 10μH, C = 4.7μF
23
15
μA
μA
BAT_NL_BM
BAT_SLP
EN_CHRG
BAT
●
Battery Current in SLEEP Mode
V
V
= 5V, MODE = V
,
BAT
10
20
EN_CHRG
> Regulation Voltage
OUT
●
●
V
Buck Undervoltage Lockout Voltage
V
BAT
V
BAT
Rising
Falling
2.6
2.4
2.7
2.5
2.8
2.6
V
V
UVLO_BUCK
Ω
Ω
R
R
PMOS Switch On-Resistance
NMOS Switch On-Resistance
PMOS Switch Current Limit
NMOS Switch Current Limit
NMOS Zero Current in Normal Mode
0.95
0.85
520
700
15
ON_P
ON_N
I
I
I
I
I
t
375
700
mA
mA
mA
mA
mA
μs
LIM_P
LIM_N
ZERO_CF
PEAK
Peak Current in Burst Mode Operation MODE = V
50
20
100
35
150
50
BAT
Zero Current in Burst Mode Operation
Buck Soft-Start Time
MODE = V
ZERO_BM
SS_BUCK
BAT
From the Rising Edge of EN_BUCK to 90%
of Buck Regulated Output
400
Logic
●
●
●
●
●
V
V
V
Input High Voltage
EN_CHRG, EN_BUCK, MODE Pin Low to High
EN_CHRG, EN_BUCK, MODE Pin High to Low
1.2
V
V
IH
IL
Input Low Voltage
0.4
Output Low Voltage (CHRG)
Input Current High
I
= 5mA
SINK
60
105
1
mV
μA
μA
MΩ
μA
OL
I
EN_BUCK, MODE Pins at 5.5V, V = 5V
–1
–1
1
IH
IL
BAT
I
Input Current Low
EN_CHRG, EN_BUCK, MODE Pins at GND
1
R
EN_CHRG Pin Input Resistance
CHRG Pin Leakage Current
V = 5V
EN_CHRG
1.45
3.3
1
EN_CHRG
●
I
V
BAT
= 4.5V, V
= 5V
CHRG
CHRG
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 4: Although the LTC4081 charger functions properly at 3.75V, full
charge current requires an input voltage greater than the desired final
battery voltage per ΔV
specification.
UVCL1
Note 5: The 2.8V maximum buck undervoltage lockout (V
) exit
UVLO_BUCK
Note 2: The LTC4081 is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
threshold must first be exceeded before the minimum V specification
applies.
BAT
Note 6: I
is expressed as a fraction of measured full charge current
C/10
with indicated PROG resistor.
Note 3: Failure to solder the exposed backside of the package to the PC
board ground plane will result in a thermal resistance much higher than
43°C/W.
4081f
4
LTC4081
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C, VCC = 5V, VBAT = 3.8V, unless otherwise
specified)
Battery Regulation (Float) Voltage
vs Charge Current
Battery Regulation (Float) Voltage
vs Temperature
Battery Regulation (Float) Voltage
vs VCC Supply Voltage
4.210
4.205
4.200
4.195
4.190
4.185
4.180
4.175
4.170
4.165
4.160
4.25
4.21
4.20
4.19
4.18
4.17
4.16
4.15
4.14
4.13
R
= 2k
PROG
4.20
4.15
4.10
4.05
4.00
3.95
3.90
3.85
–30 –10
30
50
70
90
4.5
V
5
6
200
CHARGE CURRENT (mA)
250
–50
10
4
5.5
0
50
100
150
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
CC
4081 G01
4081 G03
4081 G02
Charge Current vs Temperature
with Thermal Regulation
(Constant-Current Mode)
Charger FET On-Resistance
vs Temperature
PROG Pin Voltage
vs Charge Current
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
250
200
150
100
50
1.0
0.8
0.6
0.4
0.2
0
V
V
= 6V
CC
V
I
= 4V
= 350mA
R
PROG
= 2k
CC
BAT
= 3V
BAT
R
= 2k
PROG
THERMAL CONTROL
LOOP IN OPERATION
0
–30 –10
30
50
70
90
–25
0
25
50
75
25 50
125 150
–50
10
–50
100 125
0
75 100
175 200
TEMPERATURE (°C)
TEMPERATURE (°C)
CHARGE CURRENT (mA)
4081 G04
4081 G06
4081 G05
EN_CHRG, EN_BUCK and
MODE Pin Threshold Voltage
vs Temperature
EN_CHRG Pin Pulldown
Resistance vs Temperature
1.7
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
1.6
1.5
1.4
1.3
1.2
1.1
1.0
RISING
FALLING
0.50
–50 –30 –10 10
TEMPERATURE (°C)
90
30
50
70
–50 –30 –10 10
TEMPERATURE (°C)
90
30
50
70
4081 G07
4081 G08
4081f
5
LTC4081
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C, VCC = 5V, VBAT = 3.8V, unless otherwise
specified)
CHRG Pin Output
Low Voltage vs Temperature
Normalized Charge Termination
Time vs Temperature
Buck Oscillator Frequency
vs Battery Voltage
80
1.05
1.00
0.95
0.90
0.85
0.80
2.28
2.27
2.26
2.25
2.24
I
= 5mA
CHRG
70
60
50
40
30
20
10
2.23
2.22
0
–50 –30 –10 10
90
–50 –30 –10 10
TEMPERATURE (°C)
90
30
50
70
30
50
70
3.0
3.5
4.5
2.5
4.0
TEMPERATURE (°C)
BATTERY VOLTAGE (V)
4081 G09
4081 G10
4081 G11
Buck Oscillator Frequency
vs Temperature
Buck Efficiency vs Load Current
(VOUT = 1.8V)
Buck Efficiency vs Load Current
(VOUT = 1.5V)
100
80
60
40
20
0
1000
100
10
100
80
60
40
20
0
1000
2.4
2.3
2.2
2.1
2.0
1.9
1.8
V
= 3.8V
BAT
EFFICIENCY
(BURST)
V
= 4.5V
EFFICIENCY
(BURST)
BAT
100
10
EFFICIENCY
(PWM)
EFFICIENCY
POWER
POWER
(PWM)
LOSS
LOSS
V
= 2.7V
BAT
(PWM)
(PWM)
1
1
POWER LOSS
(BURST)
POWER LOSS
(BURST)
V
= 3.8V
= 1.5V
V
= 3.8V
= 1.8V
BAT
OUT
BAT
OUT
L = 10μH
0.1
0.01
0.1
0.01
V
V
L = 10μH
C = 4.7μF
C = 4.7μF
40 60
–60 –40 –20
0
20
80 100
0.01
0.1
1
10
100
1000
0.01
0.1
1
10
100
1000
TEMPERATURE (°C)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
4081 G13a
4081 G12
4081 G13
No-Load Buck Input Current
(Burst Mode Operation)
vs Battery Voltage
Buck Output Voltage
vs Battery Voltage
Buck Output Voltage
vs Temperature
1.810
1.805
1.810
35
30
25
I
= 1mA
OUT
I
= 1mA
OUT
Burst Mode
OPERATION
OUT
I
= 1mA
= 1.8V
OUT
OUT
OUT
Burst Mode
V
SET FOR 1.8V
V
SET FOR 1.8V
V
OPERATION
1.805
1.800
1.795
L = 10μH
PWM MODE
PWM MODE
1.800
1.795
20
15
10
5
1.790
1.785
1.780
1.790
1.785
1.780
0
2.5
3.0
3.5
4.0
4.5
30
–50 –30 –10 10
TEMPERATURE (˚C)
70
90
50
3.5
BATTERY VOLTAGE (V)
2.5
3.0
4.0
4.5
BATTERY VOLTAGE (V)
4081 G14
4081 G15
4081 G16
4081f
6
LTC4081
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C, VCC = 5V, VBAT = 3.8V, unless otherwise
specified)
No-Load Buck Input Current
(Burst Mode Operation)
vs Temperature
Buck Main Switch (PMOS)
On-Resistance vs Battery Voltage
Buck Main Switch (PMOS)
On-Resistance vs Temperature
1.2
1.0
0.8
0.6
0.4
0.2
0
35
30
1.2
1.0
0.8
0.6
0.4
0.2
0
L = 10μH
C = 4.7μF
OUT
V
= 4.2V
= 3.8V
BAT
V
= 1.8V
V
BAT
25
20
15
10
5
V
= 2.7V
BAT
0
30
TEMPERATURE (˚C)
70
90
–50 –30 –10 10
50
3.5
BATTERY VOLTAGE (V)
2.5
3.0
4.0
4.5
5.0
30
TEMPERATURE (°C)
70
90
–50 –30 –10 10
50
4081 G18
4081 G19
4081 G20
Buck Synchronous Switch (NMOS)
On-Resistance vs Battery Voltage
Buck Synchronous Switch (NMOS)
On-Resistance vs Temperature
1.2
1.0
0.8
0.6
0.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0.2
0
3.5
BATTERY VOLTAGE (V)
2.5
3.0
4.0
4.5
5.0
30
TEMPERATURE (°C)
70
90
–50 –30 –10 10
50
4081 G21
4081 G22
Maximum Output Current
(PWM Mode) vs Battery Voltage
Maximum Output Current (Burst
Mode Operation) vs Battery Voltage
500
400
300
200
100
80
70
60
50
40
30
20
10
0
L = 10μH
L = 10μH
V
SET FOR 1.8V
OUT
V
SET FOR 1.8V
OUT
2.7
3
3.3
3.6
3.9
4.2
4.5
2.7
3
3.3
3.6
3.9
4.2
4.5
BATTERY VOLTAGE (V)
BATTERY VOLTAGE (V)
4081 G24
4081 G23
4081f
7
LTC4081
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C, VCC = 5V, VBAT = 3.8V, unless otherwise
specified)
Output Voltage Waveform
when Switching Between Burst
and PWM Mode (ILOAD = 10mA)
Output Voltage Transient
Step Response (Burst Mode
Operation)
Output Voltage Transient
Step Response (PWM Mode)
V
OUT
V
V
OUT
OUT
50mV/DIV
20mV/DIV
20mV/DIV
AC COUPLED
AC COUPLED
AC COUPLED
V
I
I
MODE
LOAD
LOAD
5V/DIV
250mA/DIV
50mA/DIV
0mA
0V
0mA
4081 G27
4081 G25
4081 G26
50μs/DIV
50μs/DIV
50μs/DIV
Buck VOUT Soft-Start
(ILOAD = 50mA)
Charger VPROG Soft-Start
V
OUT
1V/DIV
0V
V
PROG
200mV/DIV
V
_
EN BUCK
0V
5V/DIV
0V
4081 G28
4081 G29
50μs/DIV
200μs/DIV
4081f
8
LTC4081
U
U
U
PI FU CTIO S
BAT (Pin 1): Charge Current Output and Buck Regulator pin below 0.016 • V disables the NTC feature. There is
CC
Input. Provides charge current to the battery and regulates approximately 3°C of temperature hysteresis associated
the final float voltage to 4.2V. An internal precision resistor with each of the input comparator’s thresholds.
dividerfromthispinsetsthefloatvoltageandisdisconnected
CHRG (Pin 6): Open-Drain Charge Status Output. The
in charger shutdown mode. This pin must be decoupled
charge status indicator pin has three states: pulldown,
with a low ESR capacitor for low-noise buck operation.
high impedance state, and pulsing at 2Hz. This output can
V (Pin2):PositiveInputSupplyVoltage.Thispinprovides be used as a logic interface or as an LED driver. When the
CC
power to the battery charger. V can range from 3.75V battery is being charged, the CHRG pin is pulled low by
CC
to 5.5V. This pin should be bypassed with at least a 1μF an internal N-channel MOSFET. When the charge current
capacitor. When V is less than 32mV above the BAT pin drops to 10% of the full-scale current, the CHRG pin is
CC
voltage, the battery charger enters shutdown mode.
forced to a high impedance state. When the battery volt-
age remains below 2.9V for one quarter of the full charge
time, the battery is considered defective, and the CHRG
pin pulses at a frequency of 2Hz with 75% duty cycle.
EN_CHRG(Pin3):EnableInputPinfortheBatteryCharger.
Pulling this pin above the manual shutdown threshold
(V ) puts the LTC4081 charger in shutdown mode, thus
IH
When the NTC pin voltage rises above 0.76 • V or drops
CC
stopping the charge cycle. In battery charger shutdown
mode, theLTC4081haslessthan10μAsupplycurrentand
less than 5μA battery drain current provided the regula-
below 0.35 • V , the CHRG pin pulses at a frequency of
CC
2Hz (25% duty cycle).
tor is not running. Enable is the default state, but the pin FB(Pin7):FeedbackPinfortheBuckRegulator. Aresistor
should be tied to GND if unused.
divider from the regulator’s output to the FB pin programs
the output voltage. Servo value for this pin is 0.8V.
PROG (Pin 4): Charge Current Program and Charge Cur-
rent Monitor Pin. Connecting a 1% resistor, R
, to MODE (Pin 8): Burst Mode Enable Pin. Tie this pin high
PROG
ground programs the charge current. When charging in to force the LTC4081 regulator into Burst Mode operation
constant-currentmode,thispinservosto1V.Inallmodes, for all load conditions. Tie this pin low to force constant-
the voltage on this pin can be used to measure the charge frequency mode operation for all load conditions. Do not
current using the following formula:
float this pin.
VPROG
RPROG
EN_BUCK(Pin9):EnableInputPinfortheBuckRegulator.
Pull this pin high to enable the regulator, pull low to shut
down. Do not float this pin.
IBAT
=
•400
NTC (Pin 5): Input to the NTC (negative temperature coef-
ficient) Thermistor Temperature Monitoring Circuit. For
normal operation, connect a thermistor from the NTC pin
to ground and a resistor of equal value from the NTC pin
SW (Pin 10): Switch Pin for the Buck Regulator. Minimize
the length of the metal trace connected to this pin. Place
the inductor as close to this pin as possible.
to V . When the voltage at this pin drops below 0.35 • GND (Pin 11): Ground. This pin is the back of the Exposed
CC
V
at hot temperatures or rises above 0.76 • V at cold, PadpackageandmustbesolderedtothePCBforelectrical
CC
CC
charging is suspended, the internal timer is frozen and the connection and rated thermal performance.
CHRG pin output will start to pulse at 2Hz. Pulling this
4081f
9
LTC4081
W
BLOCK DIAGRA
2
V
CC
+
–
3
CHARGER
SHUTDOWN
EN_CHRG
C3
MP3
X1
MP1
115°C
–
+
D3
0.82V
TA
X400
R
EN
T
DIE
D1
D2
PROG
0.1V
1
BAT
–
+
–
+
MA
C1
R1
R2
CA
VA
–
+
–
+
MP4
6
1.22V
1V
CHRG
CHARGER
ENABLE
PULSE
LOGIC
0.1V
+
–
2.9V
BAT
C2
BADBAT
V
+
CC
UVLO
C4
C5
3.6V
4
–
PROG
R
PROG
+
–
V
CC
R9
CHARGE
CONTROL
V
CC
V
BAT
+ 80mV
–
TOO COLD
TOO HOT
NTC_EN
R
NOM
C8
SUSPEND
LOGIC
NTC
+
5
R10
CHARGER
OSCILLATOR
R
T
NTC
COUNTER
–
C9
+
R11
R12
+
C10
–
LINEAR BATTERY CHARGER
MP2
+
–
SYNCHRONOUS BUCK CONVERTER
9
8
L1
PWM
CONTROL
AND DRIVE
V
C
OUT
EN_BUCK
ENABLE BUCK
C6
10
7
SW
MN1
0.82V
C
R7
R8
PL
–
+
–
OUT
2.25MHz
BUCK
OSCILLATOR
ERROR
AMP
MODE
FB
C7
+
0.8V
0.82V
11
4081 BD
GND
Figure 1. LTC4081 Block Diagram
4081f
10
LTC4081
U
OPERATIO
The LTC4081 is a full-featured linear battery charger with
an integrated synchronous buck converter designed pri-
marily for handheld applications. The battery charger is
capable of charging single-cell 4.2V Li-Ion batteries. The
buck converter is powered from the BAT pin and has a
programmable output voltage providing a maximum load
current of 300mA. The converter and the battery charger
can run simultaneously or independently of each other.
to typical, rather than worst-case, ambient temperatures
for a given application with the assurance that the battery
chargerwillautomaticallyreducethecurrentinworst-case
conditions.
An internal timer sets the total charge time, t
(typi-
TIMER
cally 4.5 hours). When this time elapses, the charge cycle
terminates and the CHRG pin assumes a high impedance
state even if C/10 has not yet been reached. To restart
the charge cycle, remove the input voltage and reapply
BATTERY CHARGER OPERATION
it or momentarily force the EN_CHRG pin above V . A
IH
new charge cycle will automatically restart if the BAT pin
Featuring an internal P-channel power MOSFET, MP1,
the battery charger uses a constant-current/constant-
voltage charge algorithm with programmable current.
Charge current can be programmed up to 500mA with a
final float voltage of 4.2V 0.5%. The CHRG open-drain
status output indicates when C/10 has been reached. No
blocking diode or external sense resistor is required; thus,
the basic charger circuit requires only two external com-
ponents. An internal charge termination timer adheres to
battery manufacturer safety guidelines. Furthermore, the
LTC4081 battery charger is capable of operating from a
USB power source.
voltage falls below V
(typically 4.1V).
RECHRG
Constant-Current / Constant-Voltage /
Constant-Temperature
The LTC4081 battery charger uses a unique architecture
to charge a battery in a constant-current, constant-volt-
age and constant-temperature fashion. Figure 1 shows a
Simplified Block Diagram of the LTC4081. Three of the
amplifier feedback loops shown control the constant-cur-
rent,CA,constant-voltage,VA,andconstant-temperature,
TAmodes.Afourthamplifierfeedbackloop,MA,isusedto
increase the output impedance of the current source pair,
MP1 and MP3 (note that MP1 is the internal P-channel
power MOSFET). It ensures that the drain current of MP1
is exactly 400 times the drain current of MP3.
A charge cycle begins when the voltage at the V pin
CC
rises above 3.6V and approximately 82mV above the BAT
pin voltage, a 1% program resistor is connected from the
PROGpintoground, andtheEN_CHRGpinispulledbelow
the shutdown threshold (V ).
IL
Amplifiers CA and VA are used in separate feedback loops
to force the charger into constant-current or constant-
voltage mode, respectively. Diodes D1 and D2 provide
priority to either the constant-current or constant-voltage
loop, whichever is trying to reduce the charge current the
most.Theoutputoftheotheramplifiersaturateslowwhich
effectively removes its loop from the system. When in
constant-currentmode,CAservosthevoltageatthePROG
pin to be precisely 1V. VA servos its non-inverting input
to 1.22V when in constant-voltage mode and the internal
resistor divider made up of R1 and R2 ensures that the
battery voltage is maintained at 4.2V. The PROG pin volt-
age gives an indication of the charge current anytime in
the charge cycle, as discussed in “Programming Charge
Current” in the Applications Information section.
When the BAT pin approaches the final float voltage of
4.2V, the battery charger enters constant-voltage mode
and the charge current begins to decrease. When the
current drops to 10% of the full-scale charge current, an
internalcomparatorturnsofftheN-channelMOSFETdriving
the CHRG pin, and the pin becomes high impedance.
An internal thermal limit reduces the programmed charge
current if the die temperature attempts to rise above a
presetvalueofapproximately115°C. Thisfeatureprotects
the LTC4081 from excessive temperature and allows the
user to push the limits of the power handling capability
of a given circuit board without the risk of damaging the
LTC4081 or external components. Another benefit of the
thermal limit is that charge current can be set according
4081f
11
LTC4081
U
OPERATIO
If the die temperature starts to creep up above 115°C
due to internal power dissipation, the transconductance
amplifier, TA, limits the die temperature to approximately
115°C by reducing the charge current. Diode D3 ensures
that TA does not affect the charge current when the die
temperature is below 115°C. In thermal regulation, the
PROG pin voltage continues to give an indication of the
charge current.
for one quarter of the total time (1.125 hr), the battery is
assumed to be defective, the charge cycle terminates and
the CHRG pin output pulses at a frequency of 2Hz with
a 75% duty cycle. If, for any reason, the battery voltage
rises above 2.9V, the charge cycle will be restarted. To
restart the charge cycle (i.e., when the dead battery is
replaced with a discharged battery less than 2.9V), the
charger must be reset by removing the input voltage and
reapplyingitortemporarilypullingtheEN_CHRGpinabove
the shutdown threshold.
In typical operation, the charge cycle begins in constant-
currentmodewiththecurrentdeliveredtothebatteryequal
to 400V/R
. If the power dissipation of the LTC4081
PROG
Battery Charger Shutdown Mode
resultsinthejunctiontemperatureapproaching115°C,the
amplifier (TA) will begin decreasing the charge current to
limit the die temperature to approximately 115°C. As the
battery voltage rises, the LTC4081 either returns to full
constant-current mode or enters constant-voltage mode
straight from constant-temperature mode.
The LTC4081’s battery charger can be disabled by pulling
the EN_CHRG pin above the shutdown threshold (V ).
IH
In shutdown mode, the battery drain current is reduced
to about 2μA and the V supply current to about 5μA
CC
provided the regulator is off. When the input voltage is
not present, the battery charger is in shutdown and the
battery drain current is less than 5μA.
Battery Charger Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the V
CC
CHRG Status Output Pin
input voltage and keeps the battery charger off until VCC
rises above 3.6V and approximately 82mV above the BAT
pin voltage. The 3.6V UVLO circuit has a built-in hysteresis
of approximately 0.6V, and the 82mV automatic shutdown
threshold has a built-in hysteresis of approximately 50mV.
During undervoltage lockout conditions, maximum battery
Thechargestatusindicatorpinhasthreestates:pulldown,
pulsing at 2Hz (see Trickle Charge and Defective Battery
Detection and Battery Temperature Monitoring) and high
impedance. The pulldown state indicates that the battery
charger is in a charge cycle. A high impedance state indi-
cates that the charge current has dropped below 10% of
the full-scale current or the battery charger is disabled.
When the timer runs out (4.5 hrs), the CHRG pin is also
forced to the high impedance state. If the battery charger
is not in constant-voltage mode when the charge current
is forced to drop below 10% of the full-scale current by
UVCL, CHRG will stay in the strong pulldown state.
drain current is 5μA and maximum supply current is 10μA.
Undervoltage Charge Current Limiting (UVCL)
The battery charger in the LTC4081 includes undervoltage
charge current limiting that prevents full charge current
untiltheinputsupplyvoltagereachesapproximately300mV
abovethebatteryvoltage(ΔV ).Thisfeatureisparticu-
UVCL1
larly useful if the LTC4081 is powered from a supply with
long leads (or any relatively high output impedance). See
Applications Information section for further details.
Charge Current Soft-Start
The LTC4081’s battery charger includes a soft-start circuit
to minimize the inrush current at the start of a charge
cycle. When a charge cycle is initiated, the charge cur-
rent ramps from zero to full-scale current over a period
of approximately 180μs. This has the effect of minimizing
the transient current load on the power supply during
start-up.
Trickle Charge and Defective Battery Detection
At the beginning of a charge cycle, if the battery volt-
age is below 2.9V, the battery charger goes into trickle
charge mode, reducing the charge current to 10% of the
programmed current. If the low battery voltage persists
4081f
12
LTC4081
U
OPERATIO
Timer and Recharge
When the charger is in Hold mode (battery temperature
is either too hot or too cold) the CHRG pin pulses in a
2Hz, 25% duty cycle frequency unless the charge task is
finished or the battery is assumed to be defective. If the
NTC pin is grounded, the NTC function will be disabled.
The LTC4081’s battery charger has an internal charge
termination timer that starts when the input voltage is
greater than the undervoltage lockout threshold and at
least 82mV above BAT, and the battery charger is leaving
shutdown.
SWITCHING REGULATOR OPERATION:
At power-up or when exiting shutdown, the charge time
is set to 4.5 hours. Once the charge cycle terminates, the
batterychargercontinuouslymonitorstheBATpinvoltage
using a comparator with a 2ms filter time. When the aver-
age battery voltage falls below 4.1V (which corresponds
to 80%-90% battery capacity), a new charge cycle is initi-
ated and a 2.25 hour timer begins. This ensures that the
battery is kept at, or near, a fully charged condition and
eliminates the need for periodic charge cycle initiations.
The CHRG output assumes a strong pulldown state dur-
ing recharge cycles until C/10 is reached or the recharge
cycle terminates.
TheswitchingbuckregulatorintheLTC4081canbeturned
on by pulling the EN_BUCK pin above V . It has two user-
IH
selectablemodesofoperation:constant-frequency(PWM)
mode and Burst Mode Operation. The constant-frequency
modeoperationofferslownoiseattheexpenseofefficiency
whereastheBurstModeoperationoffershigherefficiency
at light loads at the cost of increased noise, higher output
voltage ripple, and less output current. A detailed descrip-
tion of different operating modes and different aspects of
operation follow. Operations can best be understood by
referring to the Block Diagram.
V
CC
Battery Temperature Monitoring via NTC
The battery temperature is measured by placing a nega-
tive temperature coefficient (NTC) thermistor close to the
battery pack. The NTC circuitry is shown in Figure 2.
R
NOM
–
+
0.76 • V
NTC
CC
TOO COLD
TOO HOT
To use this feature, connect the NTC thermistor, R , be-
NTC
6
tween the NTC pin and ground and a resistor, R
, from
NOM
the NTC pin to V . R
should be a 1% resistor with a
CC NOM
R
T
NTC
–
+
value equal to the value of the chosen NTC thermistor at
25°C(thisvalueis10kforaVishayNTHS0603NO1N1002J
thermistor). The LTC4081 goes into hold mode when the
value of the NTC thermistor drops to 0.53 times the value
0.35 • V
CC
CC
of R
, which corresponds to approximately 40°C, and
NOM
+
–
when the value of the NTC thermistor increases to 3.26
times the value of R , which corresponds to approxi-
NTC_ENABLE
NOM
0.016 • V
mately 0°C. Hold mode freezes the timer and stops the
charge cycle until the thermistor indicates a return to a
valid temperature. For a Vishay NTHS0603NO1N1002J
thermistor, this value is 32.6k which corresponds to ap-
proximately 0°C. The hot and cold comparators each have
approximately 3°C of hysteresis to prevent oscillation
about the trip point.
4081 F02
Figure 2. NTC Circuit Information
4081f
13
LTC4081
U
OPERATIO
Constant-Frequency (PWM) Mode Operation
comparator monitoring the FB voltage, and the inductor
current swings between a fixed I (~100mA) and I
(35mA) irrespective of the load current as long as the FB
PEAK
ZERO
The switching regulator operates in constant-frequency
(PWM) mode when the MODE pin is pulled below V . In
IL
pin voltage is less than or equal to the reference voltage
this mode, it uses a current mode architecture including
an oscillator, an error amplifier, and a PWM comparator
for excellent line and load regulation. The main switch
MP2 (P-channel MOSFET) turns on to charge the inductor
at the beginning of each clock cycle if the FB pin voltage
is less than the 0.8V reference voltage. The current into
the inductor (and the load) increases until it reaches the
peak current demanded by the error amp. At this point,
the main switch turns off and the synchronous switch
MN1 (N-channel MOSFET) turns on allowing the inductor
current to flow from ground to the load until either the
next clock cycle begins or the current reduces to the zero
of 0.8V. Once V is greater than 0.8V, the control logic
shuts off both switches along with most of the circuitry
and the regulator is said to enter into SLEEP mode. In
SLEEP mode, the regulator only draws about 20μA from
FB
the BAT pin provided that the battery charger is turned
off. When the output voltage droops about 1% from its
nominal value, the regulator wakes up and the inductor
current resumes swinging between I
and I
. The
ZERO
PEAK
output capacitor recharges and causes the regulator to
re-enter the SLEEP state if the output load remains light
enough. Thefrequencyofthisintermittentburstoperation
depends on the load current. That is, as the load current
drops further, the regulator turns on less frequently. Thus
BurstModeoperationincreasestheefficiencyatlightloads
byminimizingtheswitchingandquiescentlosses.However,
the output voltage ripple increases to about 2%.
current (I
) level.
ZERO
Oscillator: In constant-frequency mode, the switching
regulator uses a dedicated oscillator which runs at a fixed
frequency of 2.25MHz. This frequency is chosen to mini-
mize possible interference with the AM radio band.
To minimize ripple in the output voltage, the current limits
for both switches in Burst Mode operation are reduced
to about 20% of their values in the constant-frequency
mode. Also the zero current of the synchronous switch
is changed to about 35mA thereby preventing reverse
conduction through the inductor. Consequently, the regu-
lator can only deliver approximately 67mA of load current
while in Burst Mode operation. Any attempt to draw more
load current will cause the output voltage to drop out of
regulation.
Error Amplifier: The error amplifier is an internally com-
pensated transconductance (g ) amplifier with a g
m
m
of 65 μmhos. The internal 0.8V reference voltage is
compared to the voltage at the FB pin to generate a
current signal at the output of the error amplifier. This cur-
rent signal represents the peak inductor current required
to achieve regulation.
PWM Comparator: Lossless current sensing converts
the PMOS switch current signal to a voltage which is
summed with the internal slope compensation signal.
The PWM comparator compares this summed signal to
determine when to turn off the main switch. The switch
current sensing is blanked for ~12ns at the beginning of
each clock cycle to prevent false switch turn-off.
Current Limit
To prevent inductor current runaway, there are absolute
current limits (I ) on both the PMOS main switch and
LIM
the NMOS synchronous switch. These limits are internally
set at 520mA and 700mA respectively for PWM mode. If
the peak inductor current demanded by the error amplifier
Burst Mode Operation
ever exceeds the PMOS I , the error amplifier will be
LIM
Burst Mode operation can be selected by pulling the
ignored and the inductor current will be limited to PMOS
MODE pin above V . In this mode, the internal oscil-
IH
I
. In Burst Mode operation, the PMOS current limit is
LIM
lator is disabled, the error amplifier is converted into a
reduced to 100mA to minimize output voltage ripple.
4081f
14
LTC4081
U
OPERATIO
Zero Current Comparator
is blanked for ~12ns at the beginning of each clock cycle,
inductor current can build up to a dangerously high level
over a number of cycles even if there is a hard current
limit on the main PMOS switch. This is why the switching
regulator in the LTC4081 also monitors current through
the synchronous NMOS switch and imposes a hard limit
on it. If the inductor current through the NMOS switch at
the end of a discharge cycle is not below this limit, the
regulator skips the next charging cycle thereby preventing
inductor current runaway.
Thezeroorreversecurrentcomparatormonitorstheinduc-
tor current to the output and shuts off the synchronous
rectifier when this current reduces to a predetermined
value (I
). In fixed frequency mode, this is set to nega-
ZERO
tive 15mA meaning that the regulator allows the inductor
current to flow in the reverse direction (from the output to
ground through the synchronous rectifier) to a maximum
value of 15mA. This is done to ensure that the regulator
is able to regulate at very light loads without skipping any
cyclestherebykeepingoutputvoltagerippleandnoiselow
at the cost of efficiency.
Switching Regulator Undervoltage Lockout
Whenever V
is less than 2.7V, an undervoltage lock-
BAT
However, in Burst Mode operation, I
is set to positive
ZERO
out circuit keeps the regulator off, preventing unreliable
operation. However, if the regulator is already running
and the battery voltage is dropping, the undervoltage
35mA meaning that the synchronous switch is turned off
as soon as the current through the inductor to the output
decreases to 35mA in the discharge cycle. This preserves
thechargeontheoutputcapacitorandincreasestheoverall
efficiency at light loads.
comparator does not shut down the regulator until V
drops below 2.5V.
BAT
Dropout Operation
Soft-Start
When the BAT pin voltage approaches V , the duty cycle
OUT
The LTC4081 switching regulator provides soft-start in
both modes of operation by slowly charging an internal
capacitor. The voltage on this capacitor, in turn, slowly
ramps the current limits of both switches from a low value
to their respective maximum values over a period of about
of the switching regulator approaches 100%. When V
BAT
is approximately equal to V , the regulator is said to be
OUT
in dropout. In dropout, the main switch (MP2) stays on
continuously with the output voltage being equal to the
battery voltage minus the voltage drops across the main
switch and the inductor.
400μs. The soft-start capacitor is discharged completely
whenever the regulator is disabled.
Global Thermal Shutdown
Short-Circuit Protection
The LTC4081 includes a global thermal shutdown which
shuts off the entire device (battery charger and switch-
ing regulator) if the die temperature exceeds 160°C. The
LTC4081 resumes normal operation once the temperature
drops approximately 14°C.
In the event of a short circuit at the output or during
start-up, V
will be near zero volts. Since the downward
OUT
slope of the inductor current is ~V /L, the inductor
OUT
current may not get a chance to discharge enough to
avoid a runaway situation. Because the current sensing
4081f
15
LTC4081
U
W U U
APPLICATIO S I FOR ATIO
BATTERY CHARGER
Average,ratherthaninstantaneous,batterycurrentmaybe
of interest to the user. For example, when the switching
regulator operating in low-current mode is connected in
parallel with the battery, the average current being pulled
out of the BAT pin is typically of more interest than the
instantaneous current pulses. In such a case, a simple RC
filter can be used on the PROG pin to measure the average
battery current as shown in Figure 3. A 10k resistor has
been added between the PROG pin and the filter capacitor
to ensure stability.
Programming Charge Current
The battery charge current is programmed using a single
resistor from the PROG pin to ground. The charge current
is400timesthecurrentoutofthePROGpin. Theprogram
resistor and the charge current are calculated using the
following equations:
1V
IBAT
1V
RPROG
RPROG = 400 •
, IBAT = 400 •
The charge current out of the BAT pin can be determined
at any time by monitoring the PROG pin voltage and using
the following equation:
Undervoltage Charge Current Limiting (UVCL)
USB powered systems tend to have highly variable source
impedances (due primarily to cable quality and length). A
transientloadcombinedwithsuchimpedancecaneasilytrip
theUVLOthresholdandturnthebatterychargeroffunless
undervoltage charge current limiting is implemented.
VPROG
IBAT
=
•400
R
Stability Considerations
ConsiderasituationwheretheLTC4081isoperatingunder
normal conditions and the input supply voltage begins to
sag (e.g. an external load drags the input supply down).
The LTC4081 battery charger contains two control loops:
constant-voltage and constant-current. The constant-
voltage loop is stable without any compensation when a
battery is connected with low impedance leads. Excessive
lead length, however, may add enough series inductance
If the input voltage reaches V
(approximately 300mV
), undervoltage charge
UVCL
above the battery voltage, ΔV
UVCL
current limiting will begin to reduce the charge current in
an attempt to maintain ΔV between V and BAT. The
UVCL
CC
to require a bypass capacitor of at least 1μF from BAT to
LTC4081 will continue to operate at the reduced charge
current until the input supply voltage is increased or volt-
age mode reduces the charge current further.
GND. Furthermore, a 4.7μF capacitor with a 0.2Ω to 1Ω
series resistor from BAT to GND is required to keep ripple
voltage low when the battery is disconnected.
In constant-current mode, the PROG pin voltage is in
the feedback loop, not the battery voltage. Because of
the additional pole created by PROG pin capacitance,
capacitance on this pin must be kept to a minimum. With
no additional capacitance on the PROG pin, the battery
charger is stable with program resistor values as high
as 25k. However, additional capacitance on this node
reduces the maximum allowed program resistor. The pole
frequency at the PROG pin should be kept above 100kHz.
Therefore, if the PROG pin is loaded with a capacitance,
LTC4081
CHARGE
10k
CURRENT
PROG
MONITOR
CIRCUITRY
GND
R
C
FILTER
PROG
4081 F03
Figure 3. Isolating Capacitive Load
on PROG Pin and Filtering
C
, the following equation should be used to calculate
PROG
the maximum resistance value for R
:
PROG
1
RPROG
≤
2π • 100kHz • CPROG
4081f
16
LTC4081
U
W U U
APPLICATIO S I FOR ATIO
Operation from Current Limited Wall Adapter
USB and Wall Adapter Power
Although the LTC4081 allows charging from a USB port,
a wall adapter can also be used to charge Li-Ion batter-
ies. Figure 4 shows an example of how to combine wall
adapter and USB power inputs. A P-channel MOSFET,
MP1, is used to prevent back conducting into the USB
port when a wall adapter is present and Schottky diode,
D1, is used to prevent USB power loss through the 1k
pulldown resistor.
By using a current limited wall adapter as the input sup-
ply, the LTC4081 can dissipate significantly less power
when programmed for a current higher than the limit of
the wall adapter.
Considerasituationwhereanapplicationrequiresa200mA
charge current for a discharged 800mAh Li-Ion battery.
If a typical 5V (non-current limited) input supply is avail-
able then the peak power dissipation inside the part can
exceed 300mW.
Typically a wall adapter can supply significantly more
current than the current-limited USB port. Therefore, an
N-channel MOSFET, MN1, and an extra program resistor
can be used to increase the charge current when the wall
adapter is present.
Now consider the same scenario, but with a 5V input
supply with a 200mA current limit. To take advantage
of the supply, it is necessary to program the LTC4081
to charge at a current greater than 200mA. Assume that
the LTC4081 charger is programmed for 300mA (i.e.,
Power Dissipation
R
PROG
= 1.33kΩ) to ensure that part tolerances maintain
The conditions that cause the LTC4081 battery charger to
reduce charge current through thermal feedback can be
approximated by considering the total power dissipated
in the IC. For high charge currents, the LTC4081 power
dissipation is approximately:
a programmed current higher than 200mA. Since the
battery charger will demand a charge current higher than
the current limit of the input supply, the supply voltage
will collapse to the battery voltage plus 200mA times the
on-resistance of the internal PFET. The on-resistance of
the battery charger power device is approximately 0.7Ω
with a 5V supply. The actual on-resistance will be slightly
higher due to the fact that the input supply will have col-
lapsed to less than 5V. The power dissipated during this
phase of charging is approximately 30mW. That is a ten
times improvement over the non-current limited supply
power dissipation.
P = VCC − VBAT •IBAT + PD_BUCK
(
)
D
Where P is the total power dissipated within the IC, V
D
CC
istheinputsupplyvoltage, V isthebatteryvoltage, I
BAT
D_BUCK
BAT
is the charge current and P
due to the regulator. P
is the power dissipation
can be calculated as:
D_BUCK
⎛
⎝ η
⎞
⎠
1
PD_BUCK = VOUT •IOUT
− 1
⎜
⎟
I
5V WALL
ADAPTER
CHG
1
4
SYSTEM
LOAD
BAT
LTC4081
D1
2
(500mA)
USB
POWER
(100mA)
V
CC
+
Li-Ion
BATTERY
MP1
PROG
1k
MN1
4k
1k
4081 F04
Figure 4. Combining Wall Adapter and USB Power
4081f
17
LTC4081
U
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APPLICATIO S I FOR ATIO
Using the previous example with an ambient temperature
of 85°C, the charge current will be reduced to approxi-
mately:
Where V
is the regulated output of the switching
OUT
OUT
regulator, I
is the regulator load and η is the regulator
efficiency at that particular load.
115°C − 85°C
30°C
It is not necessary to perform worst-case power dissipa-
tion scenarios because the LTC4081 will automatically
reduce the charge current to maintain the die temperature
at approximately 115°C. However, the approximate ambi-
ent temperature at which the thermal feedback begins to
protect the IC is:
IBAT
=
=
= 232.6mA
6V − 3V • 43°C /W 129°C /A
(
)
Furthermore, the voltage at the PROG pin will change
proportionally with the charge current as discussed in the
Programming Charge Current section.
V
Bypass Capacitor
T = 115°C – PDθJA
A
CC
Many types of capacitors can be used for input bypassing;
however, caution must be exercised when using multi-layer
ceramic capacitors. Because of the self-resonant and high
Q characteristics of some types of ceramic capacitors, high
voltage transients can be generated under some start-up con-
ditions, such as connecting the battery charger input to a live
T = 115°C – (V – V ) • I
• θJA if the regulator
A
CC
BAT
BAT
is off.
Example: Consider the extreme case when an LTC4081 is
operatingfroma6Vsupplyproviding250mAtoa3VLi-Ion
battery and the regulator is off. The ambient temperature
above which the LTC4081 will begin to reduce the 250mA
charge current is approximately:
power source. Adding a 1
Ω series resistor in series with an
X5Rceramiccapacitorwillminimizestart-upvoltagetransients.
For more information, refer to Application Note 88.
T = 115°C – (6V – 3V) • (250mA) • 43°C/W
A
T = 115°C – 0.75W • 43°C/W = 115°C – 32.25°C
A
Thermistors
T = 82.75°C
A
TheLTC4081NTCtrippointsaredesignedtoworkwiththerm-
istors whose resistance-temperature characteristics follow
VishayDale’s“R-TCurve1.”TheVishayNTHS0603NO1N1002J
is an example of such a thermistor. However, Vishay Dale
has many thermistor products that follow the “R-T Curve 1”
characteristic in a variety of sizes. Furthermore, any thermis-
tor whose ratio of RCOLD to RHOT is about 5 will also work
(Vishay Dale R-T Curve 1 shows a ratio of RCOLD to RHOT of
3.266/0.5325 = 6.13).
If there is more power dissipation due to the regulator,
the thermal regulation will begin at a somewhat lower
temperature. In the above circumstances, the LTC4081
can be used above 82.75°C, but the charge current will be
reduced from 250mA. The approximate current at a given
ambient temperature can be calculated:
115°C − TA
IBAT
=
V
CC − VBAT • θ
(
)
JA
4081f
18
LTC4081
U
W U U
APPLICATIO S I FOR ATIO
Power conscious designs may want to use thermistors whose
room temperature value is greater than 10k. Vishay Dale has a
number of values of thermistor from 10k to 100k that follow
the “R-T Curve 1.” Using different R-T curves, such as Vishay
Dale“R-TCurve2”,isalsopossible.Thiscurve,combinedwith
LTC4081 internal thresholds, gives temperature trip points of
approximately 0°C (falling) and 40°C (rising), a delta of 40°C.
This delta in temperature can be moved in either direction by
changing the value of RNOM with respect to RNTC. Increasing
RNOM will move both trip points to higher temperatures. To
calculate RNOM for a shift to lower temperature for example,
use the following equation:
The nearest 1% value for RNOM is 8.66k. This is the value used
to bias the NTC thermistor to get cold and hot trip points of
approximately 0°C and 40°C respectively. To extend the delta
between the cold and hot trip points, a resistor, R1, can be
added in series with RNTC (see Figure 5). The values of the
resistors are calculated as follows:
RCOLD −RHOT
3.266 − 0.5325
RNOM
=
0.5325
3.266 − 0.5325
⎛
⎝
⎞
R1 =
• RCOLD −RHOT −R
HOT
(
)
⎜
⎟
⎠
where RNOM is the value of the bias resistor and RHOT and
RCOLD are the values of RNTC at the desired temperature trip
points. Continuing the example from before with a desired
trip point of 50°C:
RCOLD
3.266
RNOM
=
• RNTC at 25°C
where RCOLD is the resistance ratio of RNTC at the desired cold
temperature trip point. If you want to shift the trip points to
higher temperatures use the following equation:
10k • 2.816− 0.4086
3.266− 0.5325
= 8.8k, 8.87k is the nearest 1% value.
RCOLD −RHOT
3.266− 0.5325
(
)
RNOM
=
=
RHOT
0.5325
RNOM
=
• RNTC at 25°C
0.5325
3.266− 0.5325
⎛
⎞
R = 10k •
• 2.816− 0.4086 − 0.4086
(
)
⎜
⎝
⎟
⎠
1
where RHOT is the resistance ratio of RNTC at the desired hot
temperature trip point.
= 604Ω, 604 is the nearest 1% value.
V
CC
Here is an example using a 100k R-T Curve 2 thermistor
from Vishay Dale. The difference between the trip points is
40°C, from before, and we want the cold trip point to be 0°C,
which would put the hot trip point at 40°C. The RNOM needed
is calculated as follows:
R
NOM
8.87k
–
+
0.76 • V
NTC
CC
TOO COLD
TOO HOT
6
RCOLD
RNOM
=
=
• RNTC at 25°C
• 10k = 8.62k
R1
604Ω
3.266
–
+
2.816
3.266
R
NTC
T
10k
0.35 • V
CC
CC
+
–
NTC_ENABLE
0.016 • V
4081 F05
Figure 5. NTC Circuits
4081f
19
LTC4081
U
W U U
APPLICATIO S I FOR ATIO
NTC Trip Point Error
SWITCHING REGULATOR
Whena1%resistorisusedforRHOT,themajorerrorinthe40°C
trippointisdeterminedbythetoleranceoftheNTCthermistor.
A typical 100k NTC thermistor has 10% tolerance. By look-
ing up the temperature coefficient of the thermistor at 40°C,
the tolerance error can be calculated in degrees centigrade.
ConsidertheVishayNTHS0603N01N1003Jthermistor, which
has a temperature coefficient of –4%/°C at 40°C. Dividing
the tolerance by the temperature coefficient, 5%/(4%/°C) =
1.25°C, gives the temperature error of the hot trip point.
Setting the Buck Converter Output Voltage
The LTC4081 regulator compares the FB pin voltage with
aninternal0.8Vreferencetogenerateanerrorsignalatthe
output of the error amplifier. A voltage divider from V
to ground (as shown in the Block Diagram) programs the
output voltage via FB using the formula:
OUT
R7
R8
⎡
⎣
⎤
VOUT = 0.8V • 1+
⎢
⎥
⎦
The cold trip point error depends on the tolerance of the NTC
thermistor and the degree to which the ratio of its value at
0°C and its value at 40°C varies from 6.14 to 1. Therefore,
the cold trip point error can be calculated using the tolerance,
TOL, the temperature coefficient of the thermistor at 0°C, TC
(in %/°C), the value of the thermistor at 0°C, RCOLD, and the
value of the thermistor at 40°C, RHOT. The formula is:
Keeping the current low (<5μA) in these resistors maxi-
mizes efficiency, but making them too low may allow stray
capacitancetocausenoiseproblemsandreducethephase
margin of the error amp loop. To improve the frequency
response, a phase-lead capacitor (C ) of approximately
PL
10pF can be used. Great care should be taken to route the
FB line away from noise sources, such as the inductor or
the SW line.
⎛
⎞
R
RHOT
TC
1+ TOL
6.14
•
COLD −1 • 100
⎜
⎟
⎝
⎠
Temperature Error(°C)=
Inductor Selection
The value of the inductor primarily determines the cur-
rent ripple in the inductor. The inductor ripple
For example, the Vishay NTHS0603N01N1003J thermistor
with a tolerance of 5%, TC of –5%/°C and RCOLD/RHOT of
6.13, has a cold trip point error of:
current ΔI decreases with higher inductance and
L
increases with higher V or V
:
IN
OUT
1+ 0.05
6.14
⎛
⎞
⎠
⎛
⎞
⎟
⎠
VOUT
fOSC •L
VOUT
• 6.13−1 • 100
⎜
⎝
⎟
ΔIL =
• 1−
⎜
⎝
V
Temperature Error(°C)=
IN
−5
= −0.95°C, 1.05°C
4081f
20
LTC4081
U
W U U
APPLICATIO S I FOR ATIO
Table 1. Recommended Surface Mount Inductor Manufacturers
Accepting larger values of ΔI allows the use of low
L
Coilcraft
Sumida
Murata
Toko
www.coilcraft.com
www.sumida.com
www.murata.com
www.tokoam.com
inductances, but results in higher output voltage ripple,
greater core losses, and lower output current capability. A
reasonable starting point for setting ripple current is ΔI
L
=0.3 • I , where I
is the peak switch current limit.
LIM
LIM
The largest ripple current occurs at the maximum input
voltage. To guarantee that the ripple current stays below a
specified maximum, the inductor value should be chosen
according to the following equation:
Input and Output Capacitor Selection
Since the input current waveform to a buck converter is a
squarewave,itcontainsveryhighfrequencycomponents.
It is strongly recommended that a low equivalent series
resistance (ESR) multilayer ceramic capacitor be used to
bypass the BAT pin which is the input for the converter.
Tantalum and aluminum capacitors are not recommended
because of their high ESR. The value of the capacitor on
BATdirectlycontrolstheamountofinputvoltageripplefor
a given load current. Increasing the size of this capacitor
will reduce the input ripple.
⎛
⎞
⎟
VOUT
f0 • ΔIL
VOUT
L ≥
• 1−
⎜
⎜
⎝
⎟
⎠
V
IN
MAX
(
)
For applications with V
= 1.8V, the above equation
OUT
suggests that an inductor of at least 6.8μH should be used
for proper operation.
Many different sizes and shapes of inductors are
available from numerous manufacturers. To maximize
efficiency, choose an inductor with a low DC resistance.
Keep in mind that most inductors that are very thin or
have a very small volume typically have much higher core
and DCR losses and will not give the best efficiency. Also
choose an inductor with a DC current rating at least 1.5
times larger than the peak inductor current limit to ensure
that the inductor does not saturate during normal opera-
tion. To minimize radiated noise use a toroid or shielded
pot core inductor in ferrite or permalloy materials. Table
1 shows a list of several inductor manufacturers.
To prevent large V
voltage steps during transient
OUT
load conditions, it is also recommended that a ceramic
capacitor be used to bypass V . A typical value for this
OUT
capacitor is 4.7μF.
Multilayer Ceramic Chip Capacitors (MLCC) typically have
exceptional ESR performance. MLCCs combined with a
carefullylaidoutboardwithanunbrokengroundplanewill
yield very good performance and low EMI emissions.
4081f
21
LTC4081
U
W U U
APPLICATIO S I FOR ATIO
Thereareseveraltypesofceramiccapacitorswithconsider-
ablydifferentcharacteristics.Y5Vceramiccapacitorshave
apparently higher packing density but poor performance
over their rated voltage or temperature ranges. Under
given voltage and temperature conditions, X5R and X7R
ceramic capacitors should be compared directly by case
size rather than specified value for a desired minimum
capacitance.Somemanufacturersprovideexcellentdataon
theirwebsitesaboutachievablecapacitance.Table2shows
a list of several ceramic capacitor manufacturers.
Board Layout Considerations
To be able to deliver maximum charge current under all
conditions, it is critical that the exposed metal pad on the
backside of the LTC4081’s package has a good thermal
contact to the PC board ground. Correctly soldered to a
2
2500mm double-sided 1 oz. copper board, the LTC4081
has a thermal resistance of approximately 43°C/W. Failure
to make thermal contact between the exposed pad on the
backside of the package and the copper board will result
in thermal resistance far greater than 43°C/W.
Table 2. Recommended Ceramic Capacitor Manufacturers
Furthermore due to its high frequency switching circuitry,
it is imperative that the input capacitor, BAT pin capaci-
tor, inductor, and the output capacitor be as close to the
LTC4081 as possible and that there is an unbroken ground
plane under the LTC4081 and all of its high frequency
components.
Taiyo Yuden
AVX
www.t-yuden.com
www.avxcorp.com
www.murata.com
www.tdk.com
Murata
TDK
4081f
22
LTC4081
U
PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115
0.38 0.10
TYP
6
10
0.675 0.05
3.50 0.05
2.15 0.05 (2 SIDES)
1.65 0.05
3.00 0.10
(4 SIDES)
1.65 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
PACKAGE
OUTLINE
(DD) DFN 1103
5
1
0.25 0.05
0.50 BSC
0.75 0.05
0.200 REF
0.25 0.05
0.50
BSC
2.38 0.10
(2 SIDES)
2.38 0.05
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
4081f
InformationfurnishedbyLinearTechnologyCorporationisbelievedtobeaccurateandreliable.However,
no responsibility is assumed for its use. Linear Technology Corporation makes no representation that
the interconnection of its circuits as described herein will not infringe on existing patent rights.
23
LTC4081
U
TYPICAL APPLICATIO
Li-Ion Battery Charger with 1.5V Buck Regulator
Buck Efficiency vs Load Current
(VOUT = 1.5V)
D1
100
80
60
40
20
0
1000
100
10
R3
510Ω
EFFICIENCY
(Burst)
V
CC
(3.75V
TO 5.5V)
V
CHRG
BAT
CC
EFFICIENCY
500mA
POWER
LOSS
(PWM)
R
NOM
100k
EN_BUCK
LTC4081
4.2V
+
L1
C
BAT
(PWM)
Li-Ion/
1OμH
4.7μF
POLYMER
BATTERY
NTC
SW
FB
1
POWER LOSS
(Burst)
C
C
R1
715k
IN
4.7μF
PL
10pF
EN_CHRG
V
V
V
= 3.8V
= 1.5V
OUT
BAT
OUT
0.1
0.01
(1.5V/300mA)
R
NTC
100k
MODE GND PROG
T
L = 10μH
C = 4.7μF
R
R2
806k
C
PROG
806Ω
OUT
4.7μF
0.01
0.1
1
10
100
1000
4081 TA02a
LOAD CURRENT (mA)
4081 TA02b
RELATED PARTS
PART NUMBER
Battery Chargers
LTC3550
DESCRIPTION
COMMENTS
Dual Input USB/AC Adapter Li-Ion Battery Charger Synchronous Buck Converter, Efficiency: 93%, Adjustable Output: 600mA,
with Adjustable Output 600mA Buck Converter
Charge Current: 950mA Programmable, USB Compatible, Automatic Input Power
Detection and Selection
LTC3550-1
Dual Input USB/AC Adapter Li-Ion Battery Charger Synchronous Buck Converter, Efficiency: 93%, Output: 1.875V at 600mA,
with 600mA Buck Converter
Charge Current: 950mA Programmable, USB Compatible, Automatic Input Power
Detection and Selection
LTC4054
Standalone Linear Li-Ion Battery Charger with
Integrated Pass Transistor in ThinSOTTM
Thermal Regulation Prevents Overheating, C/10 Termination
LTC4061
Standalone Li-Ion Charger with Thermistor
Interface
4.2V, 0.35% Float Voltage, Up to 1A Charge Current, 3mm × 3mm
DFN Package
LTC4061-4.4
LTC4062
Standalone Li-Ion Charger with Thermistor
Interface
4.4V (Max), 0.4% Float Voltage, Up to 1A Charge Current, 3mm × 3mm
DFN Package
Standalone Linear Li-Ion Battery Charger with
Micropower Comparator
Up to 1A Charge Current, Charges from USB Port, Thermal Regulation
3mm × 3mm DFN Package
LTC4063
LTC4080
Li-Ion Charger with Linear Regulator
Up to 1A Charge Current, 100mA, 125mV LDO, 3mm × 3mm DFN Package
Standalone 500mA Charger with 300mA
Synchronous Buck
For 1-Cell Li-Ion/Polymer Batteries; Trickle Charge; Timer Termination +C/10;
Thermal Regulation, Buck Output: 0.8V to V , Buck Input: 2.7V to 5.5V, 3mm ×
BAT
3mm DFN-10 Package
Power Management
LTC3405/LTC3405A 300mA (I ), 1.5MHz, Synchronous Step-Down 95% Efficiency, V : 2.7V to 6V, V
= 0.8V, I = 20μA, I < 1μA,
Q SD
OUT
IN
OUT
DC/DC Converter
ThinSOT Package
LTC3406/LTC3406A 600mA (I ), 1.5MHz, Synchronous Step-Down 95% Efficiency, V : 2.5V to 5.5V, V
= 0.6V, I = 20μA, I < 1μA,
Q SD
OUT
IN
OUT
OUT
OUT
DC/DC Converter
ThinSOT Package
LTC3411
LTC3440
1.25A (I ), 4MHz, Synchronous Step-Down
95% Efficiency, V : 2.5V to 5.5V, V
= 0.8V, I = 60μA, I < 1μA,
Q SD
OUT
IN
DC/DC Converter
MS Package
600mA (I ), 2MHz, Synchronous Buck-Boost 95% Efficiency, V : 2.5V to 5.5V, V
= 2.5V, I = 25μA, I < 1μA,
Q SD
OUT
IN
DC/DC Converter
MS Package
LTC4411/LTC4412 Low Loss PowerPathTM Controller in ThinSOT
Automatic Switching Between DC Sources, Load Sharing, Replaces ORing Diodes
LTC4413
Dual Ideal Diode in DFN
2-Channel Ideal Diode ORing, Low Forward On-Resistance, Low Regulated
Forward Voltage, 2.5V ≤ V ≤ 5.5V
IN
ThinSOT and PowerPath are trademarks of Linear Technology Corporation.
4081f
LT 0707 • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
24
●
●
© LINEAR TECHNOLOGY CORPORATION 2007
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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