LINER LTC1731EMS8-4.1

Final Electrical Specifications
LTC1731-4.1
Lithium-Ion Linear
Battery Charger Controller
April 2000
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DESCRIPTION
FEATURES
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The LTC ®1731-4.1 is a complete constant-current/constant-voltage linear charge controller for lithium-ion batteries. Nickel-cadmium (NiCd) and nickel-metal-hydride
(NiMH) batteries can also be charged with constant
current using external termination. The external sense
resistor sets the charge current with 5% accuracy. An
internal resistor divider and precision reference set the
final float potential with 1% accuracy. The output float
voltage is set internally to 4.1V.
Complete Linear Charger Controller for
1-Cell Lithium-Ion Batteries
1% Voltage Accuracy
Programmable Charge Current
C/10 Charge Current Detection Output
Programmable Charge Termination Timer
Space Saving, Thin 8-Pin MSOP Package
Automatic Sleep Mode When Input Supply
is Removed (7µA Battery Drain)
Automatic Trickle Charging of Low Voltage Cells
Programmable for Constant-Current-Only Mode
When the input supply is removed, the LTC1731 automatically enters a low current sleep mode, dropping the battery
drain current to 7µA typically. An internal comparator
detects the end-of-charge (C/10) condition while a programmable timer, using an external capacitor, sets the
total charge time. Fully discharged cells are automatically
trickle charged at 10% of the programmed current until
cell voltage exceeds 2.457V.
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APPLICATIONS
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Cellular Phones
Handheld Computers
Charging Docks and Cradles
Programmable Current Source
The LTC1731-4.1 is available in the 8-pin MSOP and SO
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
500mA Li-Ion Charger
VIN
5V TO 12V
MBRM120T3
7
1k
CHARGE
STATUS
VCC
SENSE
2
DRV
CHRG
RSENSE
0.2Ω
8
6
Q1
Si9430DY
LTC1731-4.1
3
CTIMER
0.1µF
TIMER
BAT
PROG
GND
4
1µF
IBAT = 500mA
1
5
RPROG*
19.6k
+ Li-ION
10µF
CELL
1731 TA01
*SHUTDOWN INVOKED BY FLOATING THE PROG PIN
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.
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LTC1731-4.1
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ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (VCC) ................................... 13.2V
Input Voltage (SENSE, DRV, BAT,
TIMER, PROG) ....................... – 0.3V to (VCC + 0.3V)
Output Voltage (CHRG) ......................... – 0.3V to 13.2V
Operating Temperature Range (Note 2) .....– 40° to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
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PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
TOP VIEW
BAT
CHRG
TIMER
GND
1
2
3
4
8
7
6
5
SENSE
VCC
DRV
PROG
MS8 PACKAGE
8-LEAD PLASTIC MSOP
LTC1731EMS8-4.1
MS8 PART MARKING
ORDER PART
NUMBER
TOP VIEW
BAT 1
8
SENSE
CHRG 2
7
VCC
TIMER 3
6
DRV
GND 4
5
PROG
LTC1731ES8-4.1
S8 PART MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 150°C, θJA = 180°C/W
LTJK
173141
TJMAX = 150°C, θJA = 125°C/W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 6V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
VCC
Input Supply Voltage
ICC
Input Supply Current
Charger On, Current Mode
Shutdown Mode
Sleep Mode (Battery Drain Current)
●
●
VBAT
Regulated Output Voltage
(5V ≤ VCC ≤ 12V)
●
IBAT
Current Mode Charge Current
RPROG = 19.6k, RSENSE = 0.2Ω
RPROG = 19.6k, RSENSE = 0.2Ω
RPROG = 97.6k, RSENSE = 0.2Ω
TYP
UNITS
12
V
1
1
7
3
2
20
mA
mA
µA
4.059
4.1
4.141
500
●
465
415
70
mA
mA
mA
●
4.5
MAX
V
100
535
585
130
ITRIKL
Trickle Charge Current
VBAT = 2V, RPROG = 19.6k, ITRIKL = (VCC – VSENSE)/0.2Ω
●
30
50
100
mA
VTRIKL
Trickle Charge Threshold Voltage
From Low to High
●
2.35
2.457
2.55
V
VUV
VCC Undervoltage Lockout Voltage
From Low to High
●
4.1
4.5
∆VUV
VCC Undervoltage Lockout Hysteresis
VMSD
Manual Shutdown Threshold Voltage
2
200
PROG Pin Low to High
PROG Pin High to Low
2.457
2.446
V
mV
V
V
LTC1731-4.1
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 6V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
VASD
Automatic Shutdown Threshold Voltage
(VCC – VBAT) High to Low
(VCC – VBAT) Low to High
VDIS
Voltage Mode Disable Threshold Voltage
VTIMER
IPROG
PROG Pin Current
Internal Pull-Up Current, No RPROG
PROG Pin Load Regulation
PROG Pin Source Current, ∆VPROG ≤ 5mV
VPROG
PROG Pin Voltage
RPROG =19.6k
ICHRG
CHRG Pin Weak Pull-Down Current
VCHRG = 1V
VCHRG
CHRG Pin Output Low Voltage
ICHRG = 5mA
IC/10
End of Charge Indication Current Level
RPROG = 19.6k, RSENSE = 0.2Ω
tTIMER
TIMER Accuracy
CTIMER = 0.1µF
10
%
VCLAMP
DRV Pin Clamp Voltage
VCLAMP = VCC – VDRV, IDRIVE = 50µA
6.5
V
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
MIN
TYP
MAX
UNITS
30
40
54
69
90
100
mV
mV
●
5.6
●
300
V
µA
2.5
µA
2.457
50
●
25
V
100
150
µA
0.6
1.2
V
50
100
mA
Note 2: The LTC1731-4.1 is guaranteed to meet performance
specifications from 0°C to 70°C. Specifications over the – 40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls. Guaranteed I grade parts are
available, consult factory.
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PIN FUNCTIONS
BAT (Pin 1): Battery Sense Input. A bypass capacitor of at
least 10µF is required to keep the loop stable when the
battery is not connected. A precision internal resistor
divider sets the final float potential on this pin. The resistor
divider is disconnected in sleep mode.
CHRG (Pin 2): Open-Drain Charge Status Output. When
the battery is being charged, the CHRG pin is pulled low by
an internal N-channel MOSFET. When the charge current
drops to 10% of the full-scale current for at least 0.32
seconds, the N-channel MOSFET turns off and a 100µA
current source is connected from the CHRG pin to GND.
When the timer runs out or the input supply is removed,
the current source will be disconnected and the CHRG pin
is forced into a high impedance state.
TIMER (Pin 3): Timer Capacitor and Constant-Voltage
Mode Disable Input Pin. The timer period is set by placing
a capacitor, CTIMER, to GND. The timer period is tTIMER =
(CTIMER • 3 hours)/(0.1µF). When the TIMER pin is
connected to VCC, the constant-voltage mode is disabled
and the charger will operate in constant-current mode
only. Short the TIMER pin to GND to disable the internal
timer function.
GND (Pin 4): Ground.
PROG (Pin 5): Charge Current Program and Shutdown
Input Pin. The charge current is programmed by connecting a resistor, RPROG to ground. The charge current is IBAT
= (VPROG • 800Ω)/(RPROG • RSENSE). The IC can be forced
into shutdown by floating the PROG pin and allowing the
internal 2.5µA current source to pull the pin above the
2.457V shutdown threshold voltage.
DRV (Pin 6): Drive Output Pin for the P-Channel MOSFET
or PNP Transistor. The impedance is high at this pin,
therefore, a high gain PNP pass transistor should be used.
The DRV pin is internally clamped to 6.5V below VCC.
VCC (Pin 7): Positive Input Supply Voltage. When VBAT is
within 54mV of VCC, the LTC1731 is forced into sleep
mode, dropping ICC to 7µA. VCC ranges from 4.5V to 12V
(LTC1731-4.1). Bypass this pin with a 1µF capacitor.
SENSE (Pin 8): Current Sense Input. A sense resistor,
RSENSE, must be connected from VCC to the SENSE pin.
This resistor is chosen using the following equation:
RSENSE = (VPROG • 800Ω)/(RPROG • IBAT)
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LTC1731-4.1
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BLOCK DIAGRA
VCC
7
RSENSE
SENSE
+
2
+
–
800Ω
80Ω
C1
–
CHRG
8
54mV
+
C4
–
–
C/10 STOP C/10
TIMER
+
DRV
CA
SLP
OSCILLATOR
BAT
–
SHDN
3
720Ω
LOGIC
LBO
COUNTER
6
1
C2
+
100µA
VREF
–
+
–
VA
VCC
A1
–
+
+
C3
2.5µA
VREF
2.457V
CHARGE
5
BATTERY CURRENT IBAT = (2.457V • 800Ω)/(RPROG • RSENSE)
PROG
GND
4
1731 BD
RPROG
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OPERATIO
The LTC1731 is a linear battery charger controller. The
charge current is programmed by the combination of a
program resistor (RPROG) from the PROG pin to ground
and a sense resistor (RSENSE) between the VCC and SENSE
pins. RPROG sets a program current through an internal
trimmed 800Ω resistor setting up a voltage drop from VCC
to the input of the current amplifier (CA). The current
amplifier servos the gate of the external P-channel MOSFET
to force the same voltage drop across RSENSE which sets
the charge current. When the potential at the BAT pin
approaches the preset float voltage, the voltage amplifier
(VA) will start sinking current which reduces the voltage
drop across RSENSE, thus reducing the charge current.
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Charging begins when the potential at VCC pin rises above
the UVLO level and a program resistor is connected from
the PROG pin to ground. At the beginning of the charge
cycle, if the cell voltage is below 2.457V, the charger goes
into trickle charge mode. The trickle charge current is 10%
of the full-scale current. If the cell voltage stays low for one
quarter of the total charge time, the charge sequence will
be terminated immediately.
The charger goes into the fast charge constant-current
mode after the voltage on the BAT pin rises above 2.457V.
In constant-current mode, the charge current is set by the
combination of RSENSE and RPROG.
LTC1731-4.1
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OPERATIO
When the battery approaches the final float voltage, the
charge current will begin to decrease. When the current
drops to 10% of the full-scale charge current, an internal
comparator will turn off the pull-down N-channel MOSFET
at the CHRG pin and connect a weak current source to
ground to indicate an end-of-charge (C/10) condition.
An external capacitor on the TIMER pin sets the total
charge time. After a time-out occurs, the charging will be
terminated immediately and the CHRG pin is forced to a
high impedance state. To restart the charge cycle, simply
remove the input voltage and reapply it, or float the PROG
pin momentarily.
For batteries like lithium-ion that require accurate final
float potential, the internal 2.457V reference, voltage
amplifier and the resistor divider provide regulation with
±1% (max) accuracy. For NiMH and NiCd batteries, the
LTC1731 can be turned into a current source by pulling
the TIMER pin to VCC. When in the constant-current only
mode, the voltage amplifier, timer and the trickle charge
function are all disabled.
When the input voltage is not present, the charger goes
into a sleep mode, dropping ICC to 7µA. This greatly
reduces the current drain on the battery and increases the
standby time. The charger can be shut down by floating the
PROG pin. An internal current source will pull it high and
clamp at 3.5V.
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APPLICATIONS INFORMATION
Charge Termination
Shutdown
The charger is off when any of the following conditions
exist: the voltage at the VCC pin is below 4.1V, the voltage
at the VCC pin is higher than 4.1V but is less than 54mV
above VBAT, or the PROG pin is floating. The DRV pin will
be pulled to VCC and the internal resistor divider is disconnected to reduce the current drain on the battery.
The LTC1731 can be forced into shutdown by floating the
PROG pin thus allowing the internal 2.5µA current source
to pull the pin above the 2.457V shutdown threshold
voltage. The DRV pin will then be pulled up to VCC and
turn off the external P-channel MOSFET. The internal
timer is reset in the shutdown mode.
Undervoltage Lockout (UVLO)
Programming Charge Current
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until VCC
rises above 4.1V. To prevent oscillation around
VCC = 4.1V, the UVLO circuit has built-in hysteresis.
The formula for the battery charge current (see Block
Diagram) is:
Trickle Charge and Defective Battery Detection
where RPROG is the total resistance from the PROG pin to
ground.
At the beginning of the charging sequence, if the battery
voltage is low (below 2.457V) the charger goes into trickle
mode. The charge current is dropped to 10% of the fullscale current. If the low cell voltage persists for one
quarter of the total charging time, the battery is considered
defective, the charging will be terminated and the CHRG
pin output is forced to a high impedance state.
IBAT = (IPROG)(800Ω/RSENSE)
= (2.457V/RPROG)(800Ω/RSENSE)
For example, if 0.5A charge current is needed, select a
value for RSENSE that will drop 100mV at the maximum
charge current. RSENSE = 0.1V/0.5A = 0.2Ω, then calculate:
RPROG = (2.457V/500mA)(800Ω/0.2Ω) = 19.656k
For best stability over temperature and time, 1% resistors
are recommended. The closest 1% resistor value is 19.6k.
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LTC1731-4.1
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APPLICATIONS INFORMATION
Programming the Timer
The programmable timer is used to terminate the charge.
The length of the timer is programmed by an external
capacitor at the TIMER pin. The total charge time is:
Time = (3 Hours)(CTIMER/0.1µF)
The timer starts when the input voltage greater than 4.1V
is applied and the program resistor is connected to ground.
After a time-out occurs, the CHRG output will turn into a
high impedance state to indicate that the charging has
stopped. Connecting the TIMER pin to VCC disables the
timer and also puts the charger into a constant-current
mode. To only disable the timer function, short the TIMER
pin to GND.
CHRG Status Output Pin
When the charge cycle starts, the CHRG pin is pulled down
to ground by an internal N-channel MOSFET that can drive
an LED. When the charge current drops to 10% of the fullscale current (C/10), the N-channel MOSFET is turned off
and a weak 100µA current source to ground is connected
to the CHRG pin. After a time-out occurs, the pin will go
into a high impedance state. By using two different value
pull-up resistors, a microprocessor can detect three states
from this pin (charging, C/10 and stop charging). See
Figure 1.
VDD
V+
7
VCC
100k
LTC1731-4.1
CHRG
2
µPROCESSOR
1k
OUT
IN
1731 F01
Figure 1. Microprocessor Interface
When the LTC1731 is in charge mode, the CHRG pin is
pulled down by an internal N-channel MOSFET. To detect
this mode, force the digital output pin, OUT, high and
measure the voltage at the CHRG pin. The N-channel
MOSFET will pull the pin low even with a 1k pull-up
resistor. Once the charge current drops to 10% of the full
scale current (C/10), the N-channel MOSFET is turned off
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and a 100µA current source is connected to the CHRG pin.
By forcing the OUT pin into a high impedance state, the
current source will pull the pin low through the 100k
resistor. When the internal timer has expired, the CHRG
pin will change to high impedance state and the 100k
resistor will then pull the pin high to indicate the charging
has stopped.
End of Charge (C/10)
The LTC1731 includes a comparator to monitor the charge
current to detect an end-of-charge condition. When the
battery current falls below 10% of full scale, the comparator trips and turns off the N-channel MOSFET at the CHRG
pin and switches in a 100µA current source to ground.
After an internal time delay of at least 300ms, this state is
then latched. This delay will help prevent false triggering
due to transient currents. The end-of-charge comparator
is disabled in trickle charge mode.
Gate Drive
Typically the LTC1731 controls an external P-channel
MOSFET to supply current to the battery. The DRV pin is
internally clamped to 6.5V below VCC. This feature allows
low voltage P-channel MOSFETs with gate to source
breakdown voltage rated at 8V to be used.
An external PNP transistor can also be used as the pass
transistor instead of the P-channel MOSFET. Due to the
low current gain of the current amplifier (CA), a high gain
Darlington PNP transistor is required to avoid excessive
charge current error. The gain of the current amplifier is
around 0.6µA/mV. For every 1µA of base current, a 1.6mV
of gain error shows up at the inputs of CA. With RPROG =
19.6k (100mV across RSENSE), it represents 1.67% of
error in charging current.
Constant-Current Only Mode
The LTC1731 can be used as a programmable current
source by forcing the TIMER pin to VCC. This is particularly useful for charging NiMH or NiCd batteries. In the
constant-current only mode, the timer and voltage amplifier are both disabled. An external termination method is
required to properly terminate the charge.
LTC1731-4.1
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APPLICATIONS INFORMATION
Stability
The charger is stable without any compensation when a
P-channel MOSFET is used as the pass transistor.
However, a 10µF capacitor is recommended at the BAT
pin to keep the ripple voltage low when the battery is
disconnected.
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PACKAGE DESCRIPTION
When a PNP transistor is chosen as the pass transistor, a
1000pF capacitor is required from the DRV pin to VCC. This
capacitor is needed to help stablize the voltage loop. A
10µF capacitor at the BAT pin is also recommended when
a battery is not present.
Dimensions in inches (millimeters) unless otherwise noted.
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.040 ± 0.006
(1.02 ± 0.15)
0.007
(0.18)
0.118 ± 0.004*
(3.00 ± 0.102)
0.034 ± 0.004
(0.86 ± 0.102)
8
7 6
5
0° – 6° TYP
SEATING
PLANE 0.012
(0.30)
0.0256
REF
(0.65)
BSC
0.021 ± 0.006
(0.53 ± 0.015)
0.118 ± 0.004**
(3.00 ± 0.102)
0.193 ± 0.006
(4.90 ± 0.15)
0.006 ± 0.004
(0.15 ± 0.102)
MSOP (MS8) 1098
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* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,
PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
2 3
4
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
0.016 – 0.050
(0.406 – 1.270)
0.014 – 0.019
(0.355 – 0.483)
TYP
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
8
7
6
5
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
SO8 1298
1
2
3
4
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LTC1731-4.1
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TYPICAL APPLICATIONS
Linear Charger Using a PNP Transistor
VIN
5V TO 12V
MBRM120T3
R2
1k
C1
1nF
7
VCC
SENSE
2
DRV
CHRG
R1
10k
RSENSE
0.2Ω
Q2
ZTX749
8
6
Q1
2N5087
LTC1731-4.1
3
TIMER
BAT
PROG
CTIMER
0.1µF
C3
1µF
IBAT = 500mA
1
5
GND
+
RPROG
19.6k
4
C2
10µF
Li-ION
CELL
1731 TA02
1.5A Single-Cell Battery Charger
VIN = 5V ~ 6V
D2
MBRS130LT3
R5
1k
LED
7
VCC
2
CHRG
SENSE
8
6
DRV
3
AVX0603ZC104KATIA
C1
0.1µF
TIMER
GND
4
R2
4.7Ω
Q2
Si2305DS
5
LTC1731-4.1
BAT
1
PROG
5 R4
C2
22µF
CER
R3
0.082Ω
1/4W
C4
0.47µF
C5
1µF
CER
3
4
D1
MBRS130LT3
2
22µF
CDRH6D38-220NC
TPS2829DBVR
18.2k
1%
1-CELL
Li-Ion
BATTERY
+
–
+
C3
100µF
1731 TA03
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Li-Ion Linear Battery Charge Controller
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8
Linear Technology Corporation
173141i LT/TP 0400 4K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
© LINEAR TECHNOLOGY CORPORATION 2000