LINER LTC4080 500ma standalone li-ion charger with integrated 300ma synchronous buck Datasheet

LTC4080
500mA Standalone Li-Ion
Charger with Integrated
300mA Synchronous Buck
DESCRIPTIO
U
FEATURES
■
Complete Linear Battery Charger with Integrated
Buck Converter
Battery Charger:
■ 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
■ C/10 Charge Current Detection Output
■ 5μA Supply Current in Shutdown Mode
Switching Regulator:
■ High Efficiency Synchronous Buck Converter
■ 300mA Output Current
■ 2.7V to 4.5V Input Range (Powered from BAT Pin)
■ 0.8V to V
BAT Output Range
■ MODE Pin Selects Fixed (2.25MHz) Constant-Frequency
PWM Mode or Low ICC (23μA) Burst Mode®
Operation
■ 2μA BAT Current in Shutdown Mode
U
APPLICATIO S
■
■
■
The ⎯ C⎯ H⎯ R⎯G 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 LTC4080 battery charger also includes
trickle charge, automatic recharge and soft-start (to limit
inrush current).
The LTC4080 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 current. The buck converter also features low-current highefficiency Burst Mode operation that can be selected by
the MODE pin.
The LTC4080 is available in 10-lead, low profile (0.75 mm)
3mm × 3mm DFN and MSOP Exposed Pad packages.
Wireless Headsets
Bluetooth Applications
Portable MP3 Players
Multifunction Wristwatches
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 6522118.
U
■
The LTC4080 is a complete constant-current/constantvoltage linear battery charger for a single-cell 4.2V
lithium-ion battery with an integrated 300mA synchronous buck converter. The small packages and low external
component count make the LTC4080 especially suitable for
portable applications. Furthermore, LTC4080 is specifically
designed to work within USB power specifications.
TYPICAL APPLICATIO
Buck Efficiency vs Load Current
(VOUT = 1.8V)
Li-Ion Battery Charger with 1.8V Buck Regulator
500mA
LTC4080
CIN
4.7μF
80
BAT
CBAT
4.7μF
L1, 1OμH
EN_CHRG
SW
EN_BUCK
FB
CPL
10pF
R1
1M
MODE GND PROG
RPROG
806Ω
R2
806k
+
VOUT
(1.8V/300mA)
COUT
4.7μF
4.2V
Li-Ion
BATTERY
EFFICIENCY (%)
VCC
60
40
20
4080 TA01a
0
0.01
EFFICIENCY
(Burst)
EFFICIENCY
(PWM)
100
POWER
LOSS 10
(PWM)
POWER LOSS
(Burst)
0
POWER LOSS (mW)
VCC
(3.75V
to 5.5V)
1000
100
VBAT = 3.8V 0.1
VOUT = 1.8V
L = 10μH
C = 4.7μF
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
4080 TA01b
4080fb
1
LTC4080
W W
U
W
ABSOLUTE
AXI U RATI GS (Note 1)
VCC , t < 1ms and Duty Cycle < 1% .............. – 0.3V to 7V
VCC Steady State ......................................... – 0.3V to 6V
BAT, ⎯C⎯H⎯R⎯G .................................................. – 0.3V to 6V
⎯E⎯N⎯_⎯C⎯H⎯R⎯G, PROG, ⎯A⎯C⎯P⎯R .................– 0.3V to VCC + 0.3V
MODE, EN_BUCK .......................... – 0.3V to VBAT + 0.3V
FB ............................................................... – 0.3V to 2V
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
Lead Temperature (MSE, Soldering, 10 sec) ......... 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
BAT
1
10 SW
VCC
2
9 EN_BUCK
EN_CHRG
3
PROG
4
7 FB
ACPR
5
6 CHRG
11
BAT
VCC
EN_CHRG
PROG
ACPR
8 MODE
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 110°C, θJA = 43°C/W (NOTE 3)
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
1
2
3
4
5
10
9
8
7
6
11
SW
EN_BUCK
MODE
FB
CHRG
MSE PACKAGE
10-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 40°C/W
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
LTC4080EDD#PBF
LTC4080EDD#TRPBF
LBXD
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC4080EMSE#PBF
LTC4080EMSE#TRPBF
LTCQH
10-Lead Plastic MSOP
–40°C to 85°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 temperature range, otherwise specifications are at TA = 25°C, VCC = 5V, VBAT = 3.8V, V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 0V, VEN_BUCK = VBAT, VMODE = 0V. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
3.75
5
5.5
V
2.7
3.8
4.5
V
VCC
Supply Voltage
(Note 4)
●
VBAT
Input Voltage for the Switching
Regulator
(Note 5)
●
ICC
Quiescent Supply Current (Charger On, VBAT = 4.5V (Forces IBAT and IPROG = 0),
Switching Regulator Off)
VEN_BUCK = 0
●
110
300
μA
ICC_SD
Supply Current in Shutdown (Both
Battery Charger and Switching
Regulator Off)
V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 5V, VEN_BUCK = 0, VCC > VBAT
V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 4V, VEN_BUCK = 0, VCC (3.5V) <
VBAT (4V)
●
5
2
10
μA
μA
IBAT_SD
Battery Current in Shutdown (Both
Battery Charger and Switching
Regulator Off)
V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 5V, VEN_BUCK = 0, VCC > VBAT
V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 4V, VEN_BUCK = 0, VCC (3.5V) <
VBAT (4V)
●
0.6
2
5
μA
μA
4080fb
2
LTC4080
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 5V, VBAT = 3.8V, V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 0V, VEN_BUCK = VBAT, VMODE = 0V. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VFLOAT
VBAT Regulated Output Voltage
IBAT = 2mA
IBAT = 2mA, 4.3V < VCC < 5.5V
●
4.179
4.158
4.2
4.2
4.221
4.242
V
V
IBAT
Current Mode Charge Current
RPROG = 4k; Current Mode; VEN_BUCK = 0
RPROG = 0.8k; Current Mode; VEN_BUCK = 0
●
●
90
475
100
500
110
525
mA
mA
VUVLO_CHRG
VCC Undervoltage Lockout Voltage
VCC Rising
VCC Falling
●
●
3.5
2.8
3.6
3.0
3.7
3.2
V
V
VPROG
PROG Pin Servo Voltage
0.8k ≤ RPROG ≤ 4k
●
0.98
1.0
1.02
V
VASD
Automatic Shutdown Threshold Voltage (VCC – VBAT), VCC Low to High
(VCC – VBAT), VCC High to Low
60
15
82
32
100
45
mV
mV
tSS_CHRG
Battery Charger Soft-Start Time
ITRKL
Trickle Charge Current
VBAT = 2V, RPROG = 0.8k
VTRKL
Trickle Charge Threshold Voltage
VBAT Rising
VTRHYS
Trickle Charge Threshold Voltage
Hysteresis
ΔVRECHRG
Recharge Battery Threshold Voltage
ΔVUVCL1,
ΔVUVCL2
(VCC – VBAT) Undervoltage Current
Limit Threshold Voltage
tTIMER
Termination Timer
Recharge Time
Battery Charger
180
μs
35
50
65
2.75
2.9
3.05
V
100
150
350
mV
VFLOAT – VBAT, 0°C < TA < 85°C
70
100
130
mV
IBAT = 0.9 ICHG
IBAT = 0.1 ICHG
180
90
300
130
●
3
4.5
6
hrs
●
1.5
2.25
3
hrs
hrs
●
mA
mV
mV
Low-Battery Charge Time
VBAT = 2.5V
●
0.75
1.125
1.5
IC/10
End of Charge Indication Current Level
RPROG = 2k (Note 6)
●
0.085
0.1
0.115
TLIM
Junction Temperature in ConstantTemperature Mode
115
°C
RON_CHRG
IBAT = 350mA, VCC = 4V
Power FET On-Resistance (Between
VCC and BAT)
⎯ H
⎯ R
⎯ G
⎯ Pulse VBAT = 2V
Defective Battery Detection C
Frequency
⎯ H
⎯ R
⎯ G
⎯ Pulse VBAT = 2V
Defective Battery Detection C
Frequency Duty Ratio
750
mΩ
2
Hz
75
%
fBADBAT
DBADBAT
mA/mA
Buck Converter
●
VFB
FB Servo Voltage
IFB
FB Pin Input Current
fOSC
Switching Frequency
IBAT_NL_CF
No-Load Battery Current (Continuous
Frequency Mode)
No-Load for Regulator, V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 5V,
L = 10μH, C = 4.7μF
1.9
mA
IBAT_NL_BM
No-Load Battery Current (Burst Mode
Operation)
No-Load for Regulator, V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 5V,
MODE = VBAT, L = 10μH, C = 4.7μF
23
μA
IBAT_SLP
Battery Current in SLEEP Mode
V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 5V, MODE = VBAT,
VOUT > Regulation Voltage
●
10
15
20
μA
VUVLO_BUCK
Buck Undervoltage Lockout
VBAT Rising
VBAT Falling
●
●
2.6
2.4
2.7
2.5
2.8
2.6
V
V
VFB = 0.85V
0.78
0.80
–50
●
1.8
2.25
0.82
V
50
nA
2.75
MHz
4080fb
3
LTC4080
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 5V, VBAT = 3.8V, V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 0V, VEN_BUCK = VBAT, VMODE = 0V. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
RON_P
PMOS Switch On-Resistance
0.95
Ω
RON_N
NMOS Switch On-Resistance
0.85
Ω
ILIM_P
PMOS Switch Current Limit
ILIM_N
NMOS Switch Current Limit
700
mA
IZERO_CF
NMOS Zero Current in Normal Mode
15
mA
375
TYP
520
MAX
700
UNITS
mA
IPEAK
Peak Current in Burst Mode Operation
MODE = VBAT
50
100
150
mA
IZERO_BM
Zero Current in Burst Mode Operation
MODE = VBAT
20
35
50
mA
tSS_BUCK
Buck Soft-Start Time
From the Rising Edge of EN_BUCK to 90%
of Buck Regulated Output
VIH
Input High Voltage
⎯E⎯N⎯_⎯C⎯H⎯R⎯G, EN_BUCK, MODE Pin Low to High
●
VIL
Input Low Voltage
E⎯ ⎯N⎯_⎯C⎯H⎯R⎯G, EN_BUCK, MODE Pin High to Low
●
VOL
Output Low Voltage (⎯C⎯H⎯R⎯G, ⎯A⎯C⎯P⎯R)
ISINK = 5mA
●
–1
1
μA
–1
1
μA
3.3
MΩ
400
μs
Logic
1.2
V
0.4
V
60
105
mV
IIH
Input Current High
EN_BUCK, MODE Pins at 5.5V, VBAT = 5V
●
IIL
Input Current Low
⎯E⎯N⎯_⎯C⎯H⎯R⎯G, EN_BUCK, MODE Pins at GND
●
R⎯E⎯N⎯_⎯C⎯H⎯R⎯G
⎯E⎯N⎯_⎯C⎯H⎯R⎯G Pin Input Resistance
V⎯E⎯N⎯_⎯C⎯H⎯R⎯G = 5V
I⎯C⎯H⎯R⎯G
⎯C⎯H⎯R⎯G Pin Leakage Current
VBAT = 4.5V, V⎯C⎯H⎯R⎯G = 5V
●
1
μA
I⎯A⎯C⎯P⎯R
⎯A⎯C⎯P⎯R Pin Leakage Current
VCC = 3V, V⎯C⎯H⎯R⎯G = 5V
●
1
μA
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 2: The LTC4080 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.
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.
1
1.7
Note 4: Although the LTC4080 charger functions properly at 3.75V, full
charge current requires an input voltage greater than the desired final
battery voltage per ΔVUVCL1 specification.
Note 5: The 2.8V maximum buck undervoltage lockout (VUVLO_BUCK) exit
threshold must first be exceeded before the minimum VBAT specification
applies.
Note 6: IC/10 is expressed as a fraction of measured full charge current
with indicated PROG resistor.
4080fb
4
LTC4080
TYPICAL PERFORMANCE CHARACTERISTICS
(TA = 25°C, VCC = 5V, VBAT = 3.8V, unless otherwise specified)
Battery Regulation (Float) Voltage
vs Charge Current
4.21
Battery Regulation (Float) Voltage
vs Temperature
RPROG = 2k
4.205
4.17
4.16
4.15
CHARGE CURRENT (mA)
4.18
4.195
4.190
4.185
4.180
4.175
150
100
50
4.170
4.14
VBAT RISING
200
4.200
4.19
FLOAT VOLTAGE (V)
FLOAT VOLTAGE (V)
250
4.210
RPROG = 2k
4.20
4.13
Charge Current
vs Battery Voltage
TRICKLE CHARGE
4.165
0
50
200
150
100
CHARGE CURRENT (mA)
4.160
– 50 – 30
250
50
30
10
TEMPERATURE (°C)
– 10
4080 G01
70
0
90
1
0
3
4
2
BATTERY VOLTAGE (V)
5
4080 G02a
4080 G02
Charge Current vs Temperature
with Thermal Regulation
(Constant-Current Mode)
4.25
250
4.20
200
CHARGE CURRENT (mA)
FLOAT VOLTAGE (V)
4.15
4.10
4.05
4.00
3.95
PROG Pin Voltage
vs Charge Current
1.0
VCC = 6V
VBAT = 3V
RPROG = 2k
RPROG = 2k
0.8
150
VPROG (V)
Battery Regulation (Float) Voltage
vs Supply Voltage
THERMAL CONTROL
LOOP IN OPERATION
100
0.6
0.4
0.2
50
3.90
3.85
4
4.5
5
0
–50
6
5.5
INPUT VOLTAGE (V)
–25
0
25
50
75
100
1.7
0.90
0.85
0.6
0.80
0.4
0.3
0.70
0.65
0.60
0.1
0.55
90
4080 G06
FALLING
0.75
0.2
70
1.6
RISING
RESISTANCE (MΩ)
0.7
VOLTAGE (V)
RDS(ON) (Ω)
⎯E⎯N⎯_⎯C⎯H⎯R⎯G Pin Pulldown
Resistance vs Temperature
0.95
VCC = 4V
0.8 IBAT = 350mA
0.5
50 75 100 125 150 175 200
CHARGE CURRENT (mA)
4080 G05
⎯E⎯N⎯_⎯C⎯H⎯R⎯G, EN_BUCK and
MODE Pin Threshold Voltage
vs Temperature
0.9
30
50
10
TEMPERATURE (°C)
25
4080 G04
Charger FET On-Resistance
vs Temperature
–10
0
TEMPERATURE (°C)
4080 G03
0
– 50 – 30
0
125
0.50
–50
1.5
1.4
1.3
1.2
1.1
–30
–10 10
30
50
TEMPERATURE (°C)
70
90
4080 G07
1.0
–50
–30
–10 10
30
50
TEMPERATURE (°C)
70
90
4080 G08
4080fb
5
LTC4080
TYPICAL PERFORMANCE CHARACTERISTICS
(TA = 25°C, VCC = 5V, VBAT = 3.8V, unless otherwise specified)
⎯C⎯H⎯R⎯G and ⎯A⎯C⎯P⎯R Pin Output
Low Voltage vs Temperature
80
Normalized Charger Timer
Period vs Temperature
Buck Oscillator Frequency
vs Battery Voltage
1.05
ICHRG, IACPR = 5mA
2.28
VOLTAGE (mV)
60
50
40
30
20
2.27
1.00
FREQUENCY (MHz)
NORMALIZED TIME PERIOD
70
0.95
0.90
0.85
70
0.80
–50
90
–30
–10
10
30
50
70
TEMPERATURE (°C)
4080 G09
100
VBAT = 4.5V
EFFICIENCY (%)
FREQUENCY (MHz)
2.1
2.0
20
1.9
80
0
0.01
100
1.810
Burst Mode
OPERATION
PWM MODE
1.800
1.795
1.790
60
3.0
3.5
4.0
BATTERY VOLTAGE (V)
4.5
4080 G14
100
POWER
LOSS 10
(PWM)
0
POWER LOSS
(Burst)
VBAT = 3.8V
0.1
VOUT = 1.5V
L = 10μH
C = 4.7μF
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
4080 G13a
40
20
0
0.01
No-Load Buck Input Current
(Burst Mode Operation)
vs Battery Voltage
1.805
IOUT = 1mA
VOUT SET FOR 1.8V
35
Burst Mode
OPERATION
30
PWM MODE
1.800
1.795
1.790
1.785
1.785
1.780
2.5
EFFICIENCY
(Burst)
EFFICIENCY
(PWM)
Buck Output Voltage
vs Temperature
BUCK OUTPUT VOLTAGE (V)
BUCK OUTPUT VOLTAGE (V)
1.805
80
1000
4080 G13
Buck Output Voltage
vs Battery Voltage
IOUT = 1mA
VOUT SET FOR 1.8V
100
0
POWER LOSS
(Burst)
VBAT = 3.8V
0.1
VOUT = 1.8V
L = 10μH
C = 4.7μF
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
4080 G12
1.810
100
POWER
LOSS 10
(PWM)
60
40
1000
POWER LOSS (mW)
VBAT = 2.7V
4.5
Buck Efficiency vs Load Current
(VOUT = 1.5V)
POWER LOSS (mW)
EFFICIENCY
(Burst)
EFFICIENCY
(PWM)
80
2.2
1.8
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
3.5
4.0
BATTERY VOLTAGE (V)
4080 G11
Buck Efficiency vs Load Current
(VOUT = 1.8V)
2.4
2.3
3.0
4080 G10
Buck Oscillator Frequency
vs Temperature
VBAT = 3.8V
2.24
2.22
2.5
90
EFFICIENCY (%)
–10 10
30
50
TEMPERATURE (°C)
BUCK INPUT CURRENT (μA)
–30
2.25
2.23
10
0
–50
2.26
1.780
–50 –30
IOUT = 1mA
VOUT = 1.8V
L = 10μH
25
20
15
10
5
30
50
–10 10
TEMPERATURE (˚C)
70
90
4080 G15
0
2.5
3.5
3.0
4.0
BATTERY VOLTAGE (V)
4.5
4080 G17
4080fb
6
LTC4080
TYPICAL PERFORMANCE CHARACTERISTICS
(TA = 25°C, VCC = 5V, VBAT = 3.8V, unless otherwise specified)
No-Load Buck Input Current
(Burst Mode Operation)
vs Temperature
1.2
1.2
1.0
1.0
20
VBAT = 2.7V
15
10
ON-RESISTANCE (Ω)
VBAT = 3.8V
25
0.8
0.6
0.4
0.2
5
30
50
–10 10
TEMPERATURE (˚C)
70
0
2.5
90
0.8
0.6
0.4
0.2
3.0
3.5
4.5
4.0
BATTERY VOLTAGE (V)
0
–50 –30
5.0
4080 G18
30
50
–10 10
TEMPERATURE (°C)
4080 G19
Buck Synchronous Switch (NMOS)
On-Resistance vs Battery Voltage
1.2
1.2
1.0
1.0
0.8
0.6
0.4
0.2
90
4080 G20
0.8
0.6
0.4
0.2
0
2.5
3.0
3.5
4.5
4.0
BATTERY VOLTAGE (V)
0
–50 –30
5.0
30
50
–10 10
TEMPERATURE (°C)
70
4080 G21
Maximum Output Current
(Burst Mode Operation)
80
MAXIMUM OUTPUT CURRENT (mA)
L = 10μH
VOUT SET FOR 1.8V
400
300
200
100
2.7
3
3.3
3.6
3.9
90
4080 G22
Maximum Output Current
(PWM Mode)
500
70
Buck Synchronous Switch (NMOS)
On-Resistance vs Temperature
ON-RESISTANCE (Ω)
ON-RESISTANCE (Ω)
0
–50 –30
Buck Main Switch (PMOS)
On-Resistance vs Temperature
VBAT = 4.2V
ON-RESISTANCE (Ω)
30
L = 10μH
C = 4.7μF
VOUT = 1.8V
MAXIMUM OUTPUT CURRENT (mA)
NO LOAD INPUT CURRENT (μA)
35
Buck Main Switch (PMOS)
On-Resistance vs Battery Voltage
4.2
4.5
BATTERY VOLTAGE (V)
L = 10μH
70
VOUT SET FOR 1.8V
60
50
40
30
20
10
0
2.7
3
3.3
3.6
3.9
4.2
4.5
BATTERY VOLTAGE (V)
4080X G23
4080X G24
4080fb
7
LTC4080
TYPICAL PERFORMANCE CHARACTERISTICS
specified)
(TA = 25°C, VCC = 5V, VBAT = 3.8V, unless otherwise
Output Voltage Waveform
when Switching Between Burst
and PWM Mode (ILOAD = 10mA)
Output Voltage Transient
Step Response (PWM Mode)
Output Voltage Transient
Step Response (Burst Mode)
VOUT
20mV/DIV
AC COUPLED
VOUT
50mV/DIV
AC COUPLED
VOUT
20mV/DIV
AC COUPLED
ILOAD
250mA/DIV
VMODE
5V/DIV
I=0
0V
ILOAD
50mA/DIV
I=0
4080 G25
4080 G27
50μs/DIV
50μs/DIV
Buck VOUT Soft-Start
(ILOAD = 50mA)
50μs/DIV
4080 G26
Charger VPROG Soft-Start
VOUT
1V/DIV
0V
VPROG
200mV/DIV
VEN_BUCK
5V/DIV
0V
V=0
4080 G28
200μs/DIV
50μs/DIV
4080 G29
4080fb
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LTC4080
U
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PI FU CTIO S
BAT (Pin 1): Charge Current Output and Buck Regulator
Input. Provides charge current to the battery and regulates
the final float voltage to 4.2V. An internal precision resistor
divider from this pin sets the float voltage and is disconnected
in charger shutdown mode. This pin should be decoupled
with a low ESR capacitor for low-noise buck operation.
VCC (Pin 2): Positive Input Supply Voltage. This pin provides
power to the battery charger. VCC can range from 3.75V
to 5.5V. This pin should be bypassed with at least a 1μF
capacitor. When VCC is less than 32mV above the BAT pin
voltage, the battery charger enters shutdown mode.
⎯ _⎯ C
⎯ H
⎯ R
⎯ G
⎯ (Pin 3): Enable Input Pin for the Battery Charger.
E⎯ N
Pulling this pin above the manual shutdown threshold
(VIH) puts the LTC4080 charger in shutdown mode, thus
stopping the charge cycle. In battery charger shutdown
mode, the LTC4080 has less than 10μA supply current and
less than 5μA battery drain current if the regulator is not
running. Enable is the default state, but the pin should be
tied to GND if unused.
PROG (Pin 4): Charge Current Program and Charge
Current Monitor Pin. Connecting a 1% resistor, RPROG, to
ground programs the charge current. When charging in
constant-current mode, this pin servos to 1V. In all modes,
the voltage on this pin can be used to measure the charge
current using the following formula:
I BAT
V
= PROG • 40 0
RPROG
⎯A⎯C⎯P⎯R (Pin 5): Open-Drain Power Supply Status Output.
When VCC is greater than the undervoltage lockout
threshold (3.6V) and greater than VBAT + 80mV, the ⎯A⎯C⎯P⎯R
pin will be pulled to ground; otherwise the pin is high
impedance.
⎯C⎯H⎯R⎯G (Pin 6): Open-Drain Charge Status Output. The
charge status indicator pin has three states: pulldown,
high impedance state, and pulse at 2Hz. This output can
be used as a logic interface or as an LED driver. When the
battery is being charged, the ⎯C⎯H⎯R⎯G pin is pulled low by an
internal N-channel MOSFET. When the charge current drops
to 10% of the full-scale current, the ⎯C⎯H⎯R⎯G pin is forced to
a high impedance state. When the battery voltage remains
below 2.9V for one quarter of the full charge time, the
battery is considered defective, and the ⎯C⎯H⎯R⎯G pin pulses
at a frequency of 2Hz with 75% duty cycle.
FB (Pin 7): Feedback Pin for the Buck Regulator. A resistor
divider from the regulator’s output to the FB pin programs
the output voltage. Servo value for this pin is 0.8V.
MODE (Pin 8): Burst Mode Enable Pin. Tie this pin high
to force the LTC4080 regulator into Burst Mode operation
for all load conditions. Tie this pin low to force constantfrequency mode operation for all load conditions. Do not
float this pin.
EN_BUCK (Pin 9): Enable Input Pin for the Switching
Regulator. Pull this pin high to enable the regulator, pull
low to shut down. Do not float this 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.
GND (Pin 11): Ground. This pin is the back of the Exposed
Pad package and must be soldered to the PCB for electrical
connection and rated thermal performance.
4080fb
9
LTC4080
W
BLOCK DIAGRA
2
VCC
+
EN_CHRG
0.82V
CHARGER
SHUTDOWN
C3
–
MP3
MP1
X1
REN
D3
X400
D1
PROG
0.1V
+
–
D2
115°C
+
TDIE
1
–
+
MA
C1
CA
BAT
R1
+
VA
+
–
MP4
6
1.22V
CHRG
R2
1V
PULSE
LOGIC
0.1V
CHARGER
ENABLE
+
2.9V
–
BAT
C2
CHARGE
CONTROL
BADBAT
4
LOGIC
PROG
RPROG
–
TA
–
3
+
VCC
C4
–
5
CHARGER
OSCILLATOR
3.6V
COUNTER
ACPR
+
C5
–
VBAT + 80mV
LINEAR BATTERY CHARGER
MP2
+
9
EN_BUCK
0.82V
–
SYNCHRONOUS BUCK CONVERTER
C6
L1
PWM
CONTROL
AND DRIVE
ENABLE BUCK
SW
CPL
MN1
+
0.82V
–
C7
2.25MHz
BUCK
OSCILLATOR
11
GND
R7
COUT
7
ERROR
AMP
+
MODE
–
8
VOUT
10
FB
0.8V
R8
4080 BD
Figure 1. LTC4080 Block Diagram
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LTC4080
U
OPERATIO
The LTC4080 is a full-featured linear battery charger with
an integrated synchronous buck converter designed primarily 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.
BATTERY CHARGER OPERATION
Featuring an internal P-channel power MOSFET, MP1,
the battery charger uses a constant-current/constantvoltage charge algorithm with programmable current.
Charge current can be programmed up to 500mA with a
final float voltage of 4.2V ±0.5%. The ⎯C⎯H⎯R⎯G 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
components. The ⎯A⎯C⎯P⎯R open-drain output indicates if the
VCC input voltage, and the difference between VCC and
BAT, are sufficient for charging. An internal termination
timer adheres to battery manufacturer safety guidelines.
Furthermore, the LTC4080 battery charger is capable of
operating from a USB power source.
A charge cycle begins when the voltage at the VCC pin
rises above 3.6V and approximately 80mV above the BAT
pin voltage, a 1% program resistor is connected from the
PROG pin to ground, and the ⎯E⎯N⎯_⎯C⎯H⎯R⎯G pin is pulled below
the shutdown threshold (VIL). If the battery voltage is less
than 2.9V, the battery charger begins trickle charging at
10% of the programmed charge current.
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
internal comparator turns off the N-channel MOSFET driving
the ⎯C⎯H⎯R⎯G 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
preset value of approximately 115°C. This feature protects
the LTC4080 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
LTC4080 or external components. Another benefit of the
thermal limit is that charge current can be set according
to typical, rather than worst-case, ambient temperatures
for a given application with the assurance that the battery
charger will automatically reduce the current in worst-case
conditions.
An internal timer sets the total charge time, tTIMER (typically 4.5 hours). When this time elapses, the charge cycle
terminates and the ⎯C⎯H⎯R⎯G 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
it or momentarily force the ⎯E⎯N⎯_⎯C⎯H⎯R⎯G pin above VIH. A
new charge cycle will automatically restart if the BAT pin
voltage falls below VRECHRG (typically 4.1V).
Constant-Current / Constant-Voltage /
Constant-Temperature
The LTC4080 battery charger uses a unique architecture
to charge a battery in a constant-current, constant-voltage and constant-temperature fashion. Figure 1 shows a
Simplified Block Diagram of the LTC4080. Three of the
amplifier feedback loops shown control the constant-current, CA, constant-voltage, VA, and constant-temperature,
TA modes. A fourth amplifier feedback loop, MA, is used to
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.
Amplifiers CA and VA are used in separate feedback loops
to force the charger into constant-current or constantvoltage 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. The output of the other amplifier saturates low which
effectively removes its loop from the system. When in
constant-current mode, CA servos the voltage at the PROG
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 voltage gives an indication of the charge current anytime in
the charge cycle, as discussed in “Programming Charge
Current” in the Applications Information section.
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LTC4080
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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.
In typical operation, the charge cycle begins in constantcurrent mode with the current delivered to the battery equal
to 400V/RPROG. If the power dissipation of the LTC4080
results in the junction temperature approaching 115°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 LTC4080 either returns to
constant-current mode or enters constant-voltage mode
straight from constant-temperature mode.
the ⎯C⎯H⎯R⎯G 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
⎯ _⎯ C
⎯ H
⎯ R
⎯ G
⎯ pin above
reapplying it or temporarily pulling the E⎯ N
the shutdown threshold.
Battery Charger Shutdown Mode
The LTC4080’s battery charger can be disabled by pulling
the ⎯E⎯N⎯_⎯C⎯H⎯R⎯G pin above the shutdown threshold (VIH).
In shutdown mode, the battery drain current is reduced
to less than 2μA and the VCC supply current to about 5μA
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)
Power Supply Status Indicator (⎯A⎯C⎯P⎯R)
An internal undervoltage lockout circuit monitors the
input voltage and keeps the battery charger off until VCC
rises above 3.6V and approximately 80mV above the BAT
pin voltage. The 3.6V UVLO circuit has a built-in hysteresis
of approximately 0.6V, and the 80mV automatic shutdown
threshold has a built-in hysteresis of approximately 50mV.
During undervoltage lockout conditions, maximum battery
drain current is 5μA and maximum supply current is 10μA.
The power supply status output has two states: pulldown
and high impedance. The pulldown state indicates that VCC
is above the undervoltage lockout threshold and at least
82mV above the BAT voltage (see Undervoltage Lockout).
When these conditions are not met, the ⎯A⎯C⎯P⎯R pin is high
impedance indicating that the LTC4080 is unable to charge
the battery.
Undervoltage Charge Current Limiting (UVCL)
The battery charger in the LTC4080 includes undervoltage
charge current limiting that prevents full charge current
until the input supply voltage reaches approximately 300mV
above the battery voltage (ΔVUVCL1). This feature is particularly useful if the LTC4080 is powered from a supply with
long leads (or any relatively high output impedance). See
Applications Information section for further details.
Trickle Charge and Defective Battery Detection
At the beginning of a charge cycle, if the battery voltage 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
for one quarter of the total time (1.125 hr), the battery is
assumed to be defective, the charge cycle terminates and
⎯C⎯H⎯R⎯G Status Output Pin
The charge status indicator pin has three states: pulldown,
pulse at 2Hz (see Defective Battery Detection) and high
impedance. The pulldown state indicates that the battery
charger is in a charge cycle. A high impedance state indicates 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 ⎯C⎯H⎯R⎯G 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, ⎯C⎯H⎯R⎯G will stay in the strong pulldown state.
Charge Current Soft-Start
The LTC4080’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 current ramps
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LTC4080
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OPERATIO
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.
Timer and Recharge
The LTC4080’s battery charger has an internal termination timer that starts when the input voltage is greater
than the undervoltage lockout threshold and at least
80mV above BAT, and the battery charger is leaving
shutdown.
At power-up or when exiting shutdown, the charge time
is set to 4.5 hours. Once the charge cycle terminates, the
battery charger continuously monitors the BAT pin voltage
using a comparator with a 2ms filter time. When the average battery voltage falls below 4.1V (which corresponds
to 80%-90% battery capacity), a new charge cycle is initiated 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 ⎯C⎯H⎯R⎯G output assumes a strong pulldown state during recharge cycles until C/10 is reached or the recharge
cycle terminates.
SWITCHING REGULATOR OPERATION:
The switching regulator in the LTC4080 can be turned on
by pulling the EN_BUCK pin above VIH. It has two userselectable modes of operation: constant-frequency (PWM)
mode and Burst Mode Operation. The constant-frequency
mode operation offers low noise at the expense of efficiency whereas the Burst Mode operation offers increased
efficiency at light loads at the cost of increased noise and
output voltage ripple. A detailed description of different
operating modes and different aspects of operation follow. Operations can best be understood by referring to
the Block Diagram.
Constant-Frequency (PWM) Mode Operation
The switching regulator operates in constant-frequency
(PWM) mode when the MODE pin is pulled below VIL . In
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
current (IZERO) level.
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
minimize possible interference with the AM band.
Error Amplifier: The error amplifier is an internally compensated transconductance (gm) amplifier with a gm
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
current signal is then converted into a voltage signal
(ITH), and 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 ITH and
determines 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.
Burst Mode Operation
Burst Mode operation can be selected by pulling the
MODE pin above VIH. In this mode, the internal oscillator is disabled, the error amplifier is converted into a
comparator monitoring the FB voltage, and the inductor
current swings between a fixed IPEAK (~80mA) and IZERO
(35mA) irrespective of the load current as long as the FB
pin voltage is less than or equal to the reference voltage
of 0.8V. Once VFB 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
the BAT pin provided that the battery charger is turned
off. When the output voltage droops about 1% from its
4080fb
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LTC4080
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OPERATIO
nominal value, the regulator wakes up and the inductor
current resumes swinging between IPEAK and IZERO. The
output capacitor recharges and causes the regulator to
re-enter the SLEEP state if the output load remains light
enough. The frequency of this intermittent burst operation
depends on the load current. That is, as the load current
drops further, the regulator turns on less frequently. Thus
Burst Mode operation increases the efficiency at light loads
by minimizing the switching and quiescent losses. However,
the output voltage ripple increases to about 2%.
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 regulator can only deliver approximately 55mA 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.
Current Limit
To prevent inductor current runaway, there are absolute
current limits (ILIM) on both the PMOS main switch and
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
ever exceeds the PMOS ILIM, the error amplifier will be
ignored and the inductor current will be limited to PMOS
ILIM. In Burst Mode operation, the PMOS current limit is
reduced to 80mA to minimize output voltage ripple.
Zero Current Comparator
The zero or reverse current comparator monitors the inductor current to the output and shuts off the synchronous
rectifier when this current reduces to a predetermined
value (IZERO). In fixed frequency mode, this is set to negative 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
cycles thereby keeping output voltage ripple and noise low
at the cost of efficiency.
However, in Burst Mode operation, IZERO is set to positive
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
the charge on the output capacitor and increases the overall
efficiency at light loads.
Soft-Start
The LTC4080 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
400μs. The soft-start capacitor is discharged completely
whenever the regulator is disabled.
Short-Circuit Protection
In the event of a short circuit at the output or during
start-up, VOUT will be near zero volts. Since the downward
slope of the inductor current is ~VOUT/L, the inductor
current may not get a chance to discharge enough to
avoid a runaway situation. Because the current sensing
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 LTC4080 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.
Switching Regulator Undervoltage Lockout
Whenever VBAT is less than 2.7V, an undervoltage lockout circuit keeps the regulator off, preventing unreliable
operation. However, if the regulator is already running
and the battery voltage is dropping, the undervoltage
comparator does not shut down the regulator until VBAT
drops below 2.5V.
4080fb
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LTC4080
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OPERATIO
Dropout Operation
Global Thermal Shutdown
When the BAT pin voltage approaches VOUT, the duty cycle
of the switching regulator approaches 100%. When VBAT
is approximately equal to VOUT, the regulator is said to be
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.
The LTC4080 includes a global thermal shutdown which
shuts off the entire part (both battery charger and switching regulator) if the die temperature exceeds 160°C. The
LTC4080 resumes normal operation once the temperature
drops approximately 14°C.
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APPLICATIO S I FOR ATIO
BATTERY CHARGER
Programming Charge Current
The battery charge current is programmed using a single
resistor from the PROG pin to ground. The charge current
is 400 times the current out of the PROG pin. The program
resistor and the charge current are calculated using the
following equations:
RPROG = 400 •
1V
IBAT
, IBAT = 400 •
1V
RPROG
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:
I BAT =
VPROG
• 400
RPROG
Stability Considerations
The LTC4080 battery charger contains two control loops:
constant-voltage and constant-current. The constantvoltage loop is stable without any compensation when a
battery is connected with low impedance leads. Excessive
lead length, however, may add enough series inductance
to require a bypass capacitor of at least 1μF from BAT to
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,
CPROG, the following equation should be used to calculate
the maximum resistance value for RPROG:
RPROG ≤
1
• CPROG
2π • 105
Average, rather than instantaneous, battery current may be
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 2. A 10k resistor has
been added between the PROG pin and the filter capacitor
to ensure stability.
LTC4080
10k
PROG
GND
RPROG
CFILTER
CHARGE
CURRENT
MONITOR
CIRCUITRY
4080 F02
Figure 2. Isolating Capacitive Load
on PROG Pin and Filtering
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LTC4080
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APPLICATIO S I FOR ATIO
Undervoltage Charge Current Limiting (UVCL)
USB powered systems tend to have highly variable source
impedances (due primarily to cable quality and length). A
transient load combined with such impedance can easily trip
the UVLO threshold and turn the battery charger off unless
undervoltage charge current limiting is implemented.
Consider a situation where the LTC4080 is operating under
normal conditions and the input supply voltage begins to
sag (e.g. an external load drags the input supply down).
If the input voltage reaches VUVCL (approximately 300mV
above the battery voltage, ΔVUVCL), undervoltage charge
current limiting will begin to reduce the charge current in
an attempt to maintain ΔVUVCL between VCC and BAT. The
LTC4080 will continue to operate at the reduced charge
current until the input supply voltage is increased or voltage mode reduces the charge current further.
Operation from Current Limited Wall Adapter
By using a current limited wall adapter as the input supply, the LTC4080 can dissipate significantly less power
when programmed for a current higher than the limit of
the supply.
Consider a situation where an application requires a 200mA
charge current for a discharged 800mAh Li-Ion battery.
If a typical 5V (non-current limited) input supply is available then the peak power dissipation inside the part can
exceed 300mW.
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 LTC4080 to charge
at a current greater than 200mA. Assume that the LTC4080
charger is programmed for 300mA (i.e., RPROG = 1.33kΩ)
to ensure that part tolerances maintain 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 0.75Ω with a 5V supply.
The actual on-resistance will be slightly higher due to the
fact that the input supply will have collapsed 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.
USB and Wall Adapter Power
Although the LTC4080 allows charging from a USB port,
a wall adapter can also be used to charge Li-Ion batteries. Figure 3 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.
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.
5V WALL
ADAPTER
(300mA)
USB
POWER
(200mA)
BAT
D1
2
MP1
1
ICHG
SYSTEM
LOAD
LTC4080
VCC
PROG
MN1 1.33k
1k
+
4
Li-Ion
BATTERY
2k
4080 F03
Figure 3. Combining Wall Adapter and USB Power
Power Dissipation
The conditions that cause the LTC4080 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 LTC4080 power
dissipation is approximately:
PD = ( VCC − VBAT ) • IBAT + PD _ BUCK
Where PD is the total power dissipated within the IC, VCC
is the input supply voltage, VBAT is the battery voltage, IBAT
is the charge current and PD_BUCK is the power dissipation
due to the regulator. PD_BUCK can be calculated as:
⎛1 ⎞
PD _ BUCK = VOUT • IOUT ⎜ − 1⎟
⎝η ⎠
4080fb
16
LTC4080
U
W
U
U
APPLICATIO S I FOR ATIO
Where VOUT is the regulated output of the switching
regulator, IOUT is the regulator load and η is the regulator
efficiency at that particular load.
VCC Bypass Capacitor
TA = 115°C – PDθJA
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 conditions, such as connecting the battery charger input to a live
power source. Adding a 1Ω series resistor in series with an
X5R ceramic capacitor will minimize start-up voltage transients.
For more information, refer to Application Note 88.
TA = 115°C – (VCC – VBAT) • IBAT • θJA if the regulator
is off.
SWITCHING REGULATOR
It is not necessary to perform worst-case power dissipation scenarios because the LTC4080 will automatically
reduce the charge current to maintain the die temperature
at approximately 115°C. However, the approximate ambient temperature at which the thermal feedback begins to
protect the IC is:
Example: Consider the extreme case when an LTC4080 is
operating from a 6V supply providing 250mA to a 3V Li-Ion
battery and the regulator is off. The ambient temperature
above which the LTC4080 will begin to reduce the 250mA
charge current is approximately:
TA = 115°C – (6V – 3V) • (250mA) • 43°C/W
TA = 115°C – 0.75W • 43°C/W = 115°C – 32.25°C
TA = 82.75°C
If there is more power dissipation due to the regulator,
the thermal regulation will kick in at a somewhat lower
temperature than this. In the above circumstances, the
LTC4080 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:
I BAT =
115 °C − T A
( VCC − VBAT ) • θ JA
Using the previous example with an ambient temperature
of 85°C, the charge current will be reduced to approximately:
115 °C − 85 °C
30 °C
I BAT =
=
= 2 3 2 . 6mA
(6V − 3V ) • 43°C / W 129 °C / A
Note: 1V = 1J/C = 1W/A
Furthermore, the voltage at the PROG pin will change
proportionally with the charge current as discussed in
the Programming Charge Current section.
Setting the Buck Converter Output Voltage
The LTC4080 regulator compares the FB pin voltage with
an internal 0.8V reference to generate an error signal at the
output of the error amplifier. A voltage divider from VOUT
to ground (as shown in the Block Diagram) programs the
output voltage via FB using the formula:
⎡ R7 ⎤
VOUT = 0 . 8 V • ⎢1 + ⎥
⎣ R8 ⎦
Keeping the current low (<5μA) in these resistors maximizes efficiency, but making them too low may allow stray
capacitance to cause noise problems and reduce the phase
margin of the error amp loop. To improve the frequency
response, a phase-lead capacitor (CPL) of approximately
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.
Inductor Selection
The value of the inductor primarily determines the current ripple in the inductor. The inductor ripple
current ΔIL decreases with higher inductance and
increases with higher VIN or VOUT:
ΔIL =
VOUT
f0 • L
⎛
⎞
V
• ⎜ 1 − OUT ⎟
VIN ⎠
⎝
Accepting larger values of ΔIL allows the use of low
inductances, but results in higher output voltage ripple,
greater core losses, and lower output current capability. A
4080fb
17
LTC4080
U
W
U
U
APPLICATIO S I FOR ATIO
reasonable starting point for setting ripple current is ΔIL
=0.3 • ILIM, where ILIM is the peak switch current limit.
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:
L≥
VOUT
f0 • Δ IL
⎛
VOUT ⎞
• ⎜ 1−
⎟
⎜⎝
VIN(MAX ) ⎟⎠
For applications with VOUT = 1.8V, the above equation
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 operation. To minimize radiated noise, use a toroid,
or shielded pot core inductors in ferrite or permalloy
materials. Table 1 shows a list of several inductor manufacturers.
Table 1. Recommended Surface Mount Inductor Manufacturers
Coilcraft
www.coilcraft.com
Sumida
www.sumida.com
Murata
www.murata.com
Toko
www.tokoam.com
Input and Output Capacitor Selection
Since the input current waveform to a buck converter is a
square wave, it contains very high frequency components.
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
BAT directly controls the amount of input voltage ripple for
a given load current. Increasing the size of this capacitor
will reduce the input ripple.
To prevent large VOUT voltage steps during transient
load conditions, it is also recommended that a ceramic
capacitor be used to bypass VOUT. The typical value for
this capacitor is 4.7μF.
Multilayer Ceramic Chip Capacitors (MLCC) typically have
exceptional ESR performance. MLCCs combined with a
carefully laid out board with an unbroken ground plane will
yield very good performance and low EMI emissions.
There are several types of ceramic capacitors with considerably different characteristics. Y5V and X5R ceramic
capacitors have apparently higher packing density but
poor performance over their rated voltage or temperature
ranges. Under given voltage and temperature conditions,
Y5V, X5R and X7R ceramic capacitors should be compared directly by case size rather than specified value for
a desired minimum capacitance. Some manufacturers
provide excellent data on their websites about achievable capacitance. Table 2 shows a list of several ceramic
capacitor manufacturers.
Table 2. Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden
www.t-yuden.com
AVX
www.avxcorp.com
Murata
www.murata.com
TDK
www.tdk.com
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 LTC4080’s package has a good thermal
contact to the PC board ground. Correctly soldered to a
2500mm2 double-sided 1 oz. copper board, the LTC4080
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 resistances far greater than 43°C/W.
Furthermore due to its high frequency switching circuitry,
it is imperative that the input capacitor, BAT pin capacitor, inductor, and the output capacitor be as close to the
LTC4080 as possible and that there is an unbroken ground
plane under the LTC4080 and all of its high frequency
components.
4080fb
18
LTC4080
U
PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115
TYP
6
0.38 ± 0.10
10
0.675 ±0.05
3.50 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
3.00 ±0.10
(4 SIDES)
PACKAGE
OUTLINE
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD) DFN 1103
5
0.25 ± 0.05
1
0.75 ±0.05
0.200 REF
0.50
BSC
2.38 ±0.05
(2 SIDES)
0.25 ± 0.05
0.50 BSC
2.38 ±0.10
(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
MSE Package
10-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1664 Rev B)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.794 ± 0.102
(.110 ± .004)
5.23
(.206)
MIN
0.889 ± 0.127
(.035 ± .005)
1
2.06 ± 0.102
(.081 ± .004)
1.83 ± 0.102
(.072 ± .004)
2.083 ± 0.102 3.20 – 3.45
(.082 ± .004) (.126 – .136)
10
0.50
0.305 ± 0.038
(.0197)
(.0120 ± .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
10 9 8 7 6
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
0.254
(.010)
DETAIL “A”
0° – 6° TYP
1 2 3 4 5
GAUGE PLANE
0.53 ± 0.152
(.021 ± .006)
DETAIL “A”
0.18
(.007)
0.497 ± 0.076
(.0196 ± .003)
REF
SEATING
PLANE
0.86
(.034)
REF
1.10
(.043)
MAX
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
0.1016 ± 0.0508
(.004 ± .002)
MSOP (MSE) 0307 REV B
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
4080fb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
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.
19
LTC4080
U
TYPICAL APPLICATIO
Li-Ion Battery Charger with 1.5V Buck Regulator
Buck Efficiency vs Load Current
(VOUT = 1.5V)
R3
510Ω
D1
R4, 510Ω
ACPR
D2
CIN
4.7μF
LTC4080
CHRG
EN_CHRG
SW
EN_BUCK
FB
MODE
500mA
80
BAT
GND
CBAT
4.7μF
L1, 1OμH*
CPL
10pF
PROG
RPROG
806Ω
VOUT
(1.5V/300mA)
R1
715k
R2
806k
+
4.2V
Li-Ion
BATTERY
COUT
4.7μF
4080 TA02
*COILCRAFT LPO1704-103M
EFFICIENCY (%)
VCC
1000
EFFICIENCY
(Burst)
EFFICIENCY
(PWM)
100
POWER
LOSS
10
(PWM)
60
40
20
0
0.01
POWER LOSS
(Burst)
0
POWER LOSS (mW)
VCC
(3.75V
to 5.5V)
100
VBAT = 3.8V
0.1
VOUT = 1.5V
L = 10μH
C = 4.7μF
0.01
0.1
1
10
100
1000
LOAD CURRENT (mA)
4080 G13
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
Battery Chargers
LTC3550
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
LTC4053
USB Compatible Monolithic Li-Ion Battery Charger Standalone Charger with Programmable Timer, Up to 1.25A Charge Current
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 x 3mm DFN
LTC4061-4.4
Standalone Li-Ion Charger with Thermistor
Interface
4.4V (Max), ±0.4% Float Voltage, Up to 1A Charge Current, 3mm x 3mm DFN
LTC4062
Standalone Linear Li-Ion Battery Charger with
Micropower Comparator
Up to 1A Charge Current, Charges from USB Port, Thermal Regulation 3mm x
3mm DFN
LTC4063
Li-Ion Charger with Linear Regulator
Up to 1A Charge Current, 100mA, 125mV LDO, 3mm x 3mm DFN
Power Management
LTC3405/LTC3405A 300mA (IOUT), 1.5MHz, Synchronous Step-Down 95% Efficiency, VIN: 2.7V to 6V, VOUT = 0.8V, IQ = 20μA, ISD < 1μA, ThinSOT
DC/DC Converter
Package
LTC3406/LTC3406A 600mA (IOUT), 1.5MHz, Synchronous Step-Down 95% Efficiency, VIN: 2.5V to 5.5V, VOUT = 0.6V, IQ = 20μA, ISD < 1μA, ThinSOT
DC/DC Converter
Package
LTC3411
1.25A (IOUT), 4MHz, Synchronous Step-Down
DC/DC Converter
95% Efficiency, VIN: 2.5V to 5.5V, VOUT = 0.8V, IQ = 60μA, ISD < 1μA, MS Package
LTC3440
600mA (IOUT), 2MHz, Synchronous Buck-Boost
DC/DC Converter
95% Efficiency, VIN: 2.5V to 5.5V, VOUT = 2.5V, IQ = 25μA, ISD < 1μA, 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 ≤ VIN ≤ 5.5V
ThinSOT and PowerPath are trademarks of Linear Technology Corporation.
4080fb
20 Linear Technology Corporation
LT 0807 REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2006