LINER LT1239 Backup battery management circuit Datasheet

LT1239
Backup Battery
Management Circuit
OBSOLETE:
FOR INFORMATION PURPOSES ONLY
Contact Linear Technology for Potential Replacement
DESCRIPTION
FEATURES
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Micropower Operation (IQ = 20µA)
Adjustable Regulator for Battery Charging
4.85V Regulator for Battery Regulation
Cell Voltage Equalization in 2-Cell Systems
Low-Battery Detector Protects Lithium Cells
Comparator for Automatic Power Switching
Shutdown
Output Current Sensing
Current and Thermal Limiting
Reverse Output Protection
16-Pin SO Package
Operates on 7V to 30V Input
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APPLICATIONS
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Backup Battery Management Systems for Portable
Computers
Lithium-Ion Backup Systems
NiCd Backup Systems
The LT ® 1239 is a micropower backup battery management system for portable computers and instrumentation. It contains two regulators for regulating the battery
voltage and memory voltage and a comparator for switching between main power and backup power. The first
regulator provides a constant voltage charge for the
backup batteries and is adjustable from 3.75V up to 20V.
An equalization amplifier combined with the first regulator
provides precision charge equalization for a 2-cell
lithium-ion system. A second regulator with 4.85V output
provides a regulated backup battery voltage to the memory
when main power is lost. The second regulator also
isolates the backup battery from the main 5V supply
during normal operation when the memory is being powered by the 5V supply.
A comparator is included which provides automatic
switchover from main 5V power to backup power ensuring uninterrupted power for memory and power monitor, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
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Lithium-Ion Backup System
INPUT 2
+
MAIN
BATTERY
PACK
7V TO 24V
14
120Ω* 120Ω*
10
OUT 1
INPUT 1
REGULATOR
#1
22µF
3
IMON1
SHDN1
E/A (IN)
–
GND
GND
GND
LOW-BATTERY
DETECT
+
GND
4
604k
1%
300pF
+
E/A (OUT)
5VIN
22µF
1
69.8k
1%
15
7
681k
1%
INPUT 1
5
16
INPUT 2
IN
2
3.4V
Li-Ion
CELL
8
3.4V
Li-Ion
CELL
13
5V SYSTEM
POWER
+
IN
REGULATOR
#2
OUT
–
GND
6
ADJ
SHDN2
IMON2
11
OUT 2
12
MEMORY
POWER
MANAGEMENT
* REQUIRED BY SOME SAFETY AGENCIES
SEE APPLICATIONS INFORMATION
FOR INFORMATION ON
SELECTING VALUES.
LTC1239 • TA01
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LT1239
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DESCRIPTION
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ABSOLUTE MAXIMUM RATINGS
prevents deep discharge damage to the lithium cells. Both
regulators have independent shutdown and current monitor functions.
PACKAGE/ORDER INFORMATION
(Note 1)
Input 1 Voltage ...................................................... ±30V
Input 2 Voltage ............................................. 30V, – 0.6V
Output 1 Voltage ........................................... 30V, – 0.6V
Output 2 Voltage ............................................. 6V, – 0.6V
Adjust Pin Current ................................................ 10mA
SHDN1, SHDN2 (Note 2)
Input Voltage .............................................. 6V, – 0.6V
Input Current ...................................................... 5mA
IMON1 Voltage
(Note 3) .......................... (VIN1 – 30V) < IMON1 < VIN1
IMON2 Voltage
(Note 4) .......................... (VIN2 – 30V) < IMON2 < VIN2
E/A Output Voltage (Note 5) .... – 0.6V < VE/A(OUT) < VIN2
E/A Input Voltage (Note 5) .......... – 0.6V < VE/A(IN) < VIN2
5V Input Voltage ............................................. 6V, – 0.6V
Operating Temperature Range ......................... 0 to 70°C
Junction Temperature Range .............................(Note 6)
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
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ing circuitry. A low-battery detector with a 5V threshold
powers down the second regulator and the error amplifier
to limit the discharge voltage of the backup cells. This
ORDER PART
NUMBER
TOP VIEW
ADJ 1
16 OUT 1
GND 2
15 IMON1
LT1239CS
14 INPUT 1
SHDN1 3
GND 4
13 5VIN
GND 5
12 OUT 2
SHDN2 6
11 IMON2
E/A (IN) 7
10 INPUT 2
9
E/A (OUT) 8
NC
S PACKAGE
16-LEAD PLASTIC SO
TJMAX = 100°C, θJA = 120°C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
3.700
3.650
3.750
3.750
3.800
3.825
V
V
2
10
mV
– 12
– 20
– 20
– 30
– 25
– 50
mV
mV
mV
mV
0.15
0.25
0.30
0.20
0.40
V
V
V
20
0.80
1.35
30
1.2
µA
mA
mA
40
120
nA
Regulator 1 (Notes 7, 8)
Regulated Output Voltage (VADJ = VOUT1)
VIN1 = 4.3V, IOUT = 1mA, TJ = 25°C
VIN1 = 4.8V to 24V, IOUT = 1mA to 30mA
●
Line Regulation
ILOAD = 1mA, VIN1 = 4.3V to 30V
●
Load Regulation
VIN1 = 5V, ILOAD = 1mA to 30mA, TJ = 25°C
VIN1 = 5V, ILOAD = 1mA to 30mA
VIN1 = 5V, ILOAD = 1mA to 50mA, TJ = 25°C
VIN1 = 5V, ILOAD = 1mA to 50mA
Dropout Voltage (Note 9)
ILOAD = 1mA, TJ = 25°C
ILOAD = 30mA, TJ = 25°C
ILOAD = 50mA, TJ = 25°C
Ground Pin Current (Notes 10, 11)
ILOAD = 0mA, VIN1 = 3.75V
ILOAD = 30mA, VIN1 = 3.75V
ILOAD = 50mA, VIN1 = 3.75V
Adjust Pin Bias Current (Note 12)
TJ = 25°C
2
●
●
●
LT1239
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
1.20
0.75
2.8
0.25
V
V
Regulator 1 (Notes 7, 8)
Shutdown Threshold
VOUT1 = Off to On
VOUT1 = On to Off
●
●
Shutdown Pin Current (Note 13)
VSHDN1 = 0V
●
2
4
µA
Quiescent Current in Shutdown (Note 10)
VIN1 = 24V, VSHDN1 = 0V
●
10
16
µA
Ripple Rejection
VIN1 = 5V (Avg), VRIPPLE = 0.5VP-P
fRIPPLE = 120Hz, ILOAD = 20mA, TJ = 25°C
50
59
dB
Current Limit
VIN1 = 7V, VOUT1 = 0V, TJ = 25°C
VOUT1 = VOUT1(NOM) – 100mV, TJ = 25°C
30
40
50
70
mA
mA
Reverse Output Current
VOUT1 = 3.75V, VIN1 < 3.75V
VOUT1 = 3.75V, VIN1 = Open Circuit
●
●
Current Monitor Pin Output Current
VOUT1 = 3.75V, VIMON1 = 0V, IOUT1 = 1mA
VOUT1 = 3.75V, VIMON1 = 0V, IOUT1 = 10mA
VOUT1 = 3.75V, VIMON1 = 0V, IOUT1 = 50mA
●
VIN1 = 7V, VIN2 = 0V, V5VIN = 5V, IOUT2 = 1mA
VIN1 = 7V, VIN2 = 0V, V5VIN = 5V, IOUT2 = 30mA
VIN1 = 7V, VIN2 = 0V, V5VIN = 5V, IOUT2 = 50mA
●
●
●
38
6
6
12
12
µA
µA
4.6
44
215
50
µA
µA
µA
12
110
135
40
150
220
mV
mV
mV
5.00
5.15
Comparator
Output Saturation Voltage (V5VIN – VOUT2)
Low-Battery Detector
Turn-Off Threshold
TJ = 25°C
Turn-On Threshold
TJ = 25°C
Hysteresis
TJ = 25°C
4.85
V
5.3
V
0.2
0.3
V
4.775
4.850
Regulator 2
Regulated Output Voltage
VIN2 = 6.8V, IOUT = 1mA, TJ = 25°C
Output Voltage Temperature Coefficient
4.925
– 0.5
Line Regulation
IOUT2 = 1mA, VIN2 = 5.4V to 10V
Load Regulation
VIN2 = 6.8V, ILOAD = 1mA to 30mA, TJ = 25°C
VIN2 = 6.8V, ILOAD = 1mA to 30mA
VIN2 = 6.8V, ILOAD = 1mA to 50mA, TJ = 25°C
VIN2 = 6.8V, ILOAD = 1mA to 50mA
●
●
V
mV/°C
2
5
mV
– 12
– 20
– 20
– 30
– 25
– 50
mV
mV
mV
mV
16
0.80
1.35
25
1.2
µA
mA
mA
1.20
0.75
2.8
V
V
1.7
4
µA
Ground Pin Current
ILOAD = 0mA, VIN2 = 5.4V
ILOAD = 30mA, VIN2 = 5.4V
ILOAD = 50mA, VIN2 = 5.4V
●
●
●
Shutdown Threshold
VOUT2 = Off to On
VOUT2 = On to Off
●
●
Shutdown Pin Current
VSHDN2 = 0V
●
Ripple Rejection
VIN2 = 6.4V (Avg), VRIPPLE = 0.5VP-P
fRIPPLE = 120Hz, ILOAD = 20mA, TJ = 25°C
50
58
dB
Current Limit
VIN2 = 6.8V, VOUT2 = 0V, TJ 25°C
VOUT2 = VOUT2(NOM) – 100mV, TJ = 25°C
30
40
50
70
mA
mA
Reverse Output Current
VOUT2 = 4.85V, VIN2 < 4.85V
VOUT2 = 4.85V, VIN2 = Open Circuit
●
●
Current Monitor Pin Output Current
VOUT2 = 6.8V, VIMON2 = 0V, IOUT2 = 1mA
VOUT2 = 6.8V, VIMON2 = 0V, IOUT2 = 10mA
VOUT2 = 6.8V, VIMON2 = 0V, IOUT2 = 50mA
●
VE/A(IN) = 3.4V, VIN2 = 6.8V
●
0.25
35
6
6
12
12
µA
µA
4.7
41
210
47
µA
µA
µA
3
20
nA
Error Amplifier
Bias Current
3
LT1239
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
Offset Voltage
●
Output Current Sourcing
Sinking
VIN2 = 6.8V, VE/A(IN) = 3.4V, TJ = 25°C
VIN2 = 6.8V, VE/A(IN) = 3.4V, TJ = 25°C
3
3
TYP
MAX
0
15
UNITS
mV
5
5
mA
mA
Regulator 2, Low Battery Detector and Error Amplifier
Quiescent Current
VIN2 = 6.8V, 5VIN = 0V, VE/A(IN) = 3.4V
VIN2 = 6.8V, 5VIN = 0V, VE/A(IN) = 3.4V, VPIN6 = 0V
VIN2 = 4.8V, 5VIN = 0V, VE/A(IN) = 2.4V
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: All voltages are with respect to the ground pins of the device
(pins 2, 4, 5) unless otherwise specified.
Note 2: The shutdown pin input voltage rating is required for a low
impedance source. Internal protection devices connected to the shutdown
pin will turn on and clamp the pin to approximately 7V or – 0.6V. This
range allows the use of 5V logic devices to drive the pin directly. For high
impedance sources or logic running on supply voltages greater than 5.5V,
the maximum current driven into the shutdown pin must be limited to
5mA.
Note 3: The current monitor pin for regulator 1 (pin 15) can be pulled 30V
below the input pin (pin 14). The current monitor pin must not be pulled
above the input pin.
Note 4: The current monitor pin for regulator 2 (pin 11) can be pulled 30V
below the input pin (pin 10). The current monitor pin must not be pulled
above the input pin.
Note 5: E/A (OUT) pin should not be pulled below ground or above
the voltage at Input 2.
Note 6: The device is specified to an operating temperature range of 0°C to
70°C. The device is guaranteed to be functional up to the thermal
shutdown temperature. The thermal shutdown temperature for this device
is approximately 100°C.
20
8
3
●
●
●
µA
µA
µA
30
12
6
Note 7: Operating conditions are limited by maximum junction
temperature. The regulated output specification will not apply for all
possible combinations of input voltage and output current. When
operating at maximum output current, the input voltage range must be
limited. When operating at maximum input voltage, the output current
range must be limited.
Note 8: Regulator 1 of the LT1239 is tested and specified with the adjust
pin (pin 1) tied to the output pin (pin 16). See Applications Information.
Note 9: Dropout voltage is the minimum input/output voltage required to
maintain regulation at the specified output current. In dropout, the output
voltage measured at the package pins will be equal to (VIN – VDROPOUT).
Note 10: The quiescent current of the comparator is included in the
ground pin current and quiescent current specifications for regulator 1.
The comparator output is turned off (pin 13 = 0V, pin 12 = 5V) during
these tests.
Note 11: Ground pin current for regulator 1 is tested with VIN = VOUT
(nominal) and a current source load. This means that the device is tested
in it’s dropout region. Ground pin current will decrease slightly at higher
input voltages.
Note 12: Adjust pin current flows into the adjust pin.
Note 13: Shutdown pin current at VSHDN = 0V flows out of
the shutdown pin.
Note 14: 6.8V is the nominal voltage of two lithium-ion cells.
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TYPICAL PERFORMANCE CHARACTERISTICS
5.50
5.40
START-UP THRESHOLD
5.30
5.20
5.10
SHUTDOWN THRESHOLD
5.00
–25
50
25
0
TEMPERATURE (°C)
75
100
LT1239 • TPC01
4
4.975
3.80
4.950
3.79
4.925
3.78
ADJUST PIN VOLTAGE (V)
5.60
4.90
–50
Regulator 1 Adjust Pin Voltage vs
Temperature
Regulator 2 Output Voltage vs
Temperature
REGULATOR 2 OUTPUT VOLTAGE (V)
LOW-BATTERY DETECTOR THRESHOLD (V)
Low-Battery Detector Thresholds
vs Temperature
4.900
4.875
4.850
4.825
4.800
4.775
4.750
4.725
–50
3.77
3.76
3.75
3.74
3.73
3.72
3.71
–25
25
50
0
TEMPERATURE (°C)
75
100
LT1239 • TPC02
3.70
–50
–25
25
50
0
TEMPERATURE (°C)
75
100
LT1239 • TPC03
LT1239
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TYPICAL PERFORMANCE CHARACTERISTICS
Regulator 2 IMON2 Current vs
Output Current
Regulator 1 IMON Current vs
Output Current
40
250
250
VIMON1 = 0V
200
IMON1 CURRENT (µA)
200
150
100
VIN1 = 24V
= 6.8V
V
VIN1 = 5V OUT1
VOUT1 = 3.75V
150
VIN1 = 5V
VOUT1 = 3.75V
100
50
50
VADJ (PIN 1) = VOUT (PIN 16)
35
QUIESCENT CURRENT (µA)
VIN2 = 6.8V
VIMON2 = 0V
IMON2 CURRENT (µA)
Regulator 1, Comparator Quiescent
Current vs Input Voltage, Pin 14
30
25
20
15
10
VPIN3 = 0V
(REGULATOR 1 IN SHUTDOWN)
5
0
0
0
10
0
30
40
20
OUTPUT CURRENT (mA)
10
0
50
30
40
20
OUTPUT CURRENT (mA)
Comparator Output Saturation
Voltage vs Output Current
Regulator 1 Reverse Output
Current vs Output Voltage
Regulator 2 Reverse Output
Current vs Output Voltage
350
18
250
200
150
100
50
REVERSE OUTPUT CURRENT (µA)
20
18
REVERSE OUTPUT CURRENT (µA)
20
300
16
14
12
10
8
6
4
VIN1 = 0V
ADJ (PIN 1) = VOUT (PIN 16)
2
0
30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
16
14
12
10
8
6
4
2
0
10 20
0
0
1
2
3 4 5 6 7 8
OUTPUT VOLTAGE (V)
9
0
10
1
2
3 4 5 6 7 8
OUTPUT VOLTAGE (V)
LT1239 • TPC08
LT1239 • TPC07
10
LT1239 • TPC06
400
9
10
LT1239 • TPC09
Regulator 2, Error Amp, LowBattery Detector Quiescent Current
Shutdown Pin Threshold
2.0
30
1.8
1.6
1.4
1.2
1.0
25
(OFF-TO-ON)
ILOAD = 30mA
QUIESCENT CURRENT (µA)
SHUTDOWN PIN THRESHOLD (V)
0
5
INPUT VOLTAGE, PIN 14 (V)
0
LT1239 • TPC05
LT1239 • TPC04
OUTPUT SATURATION VOLTAGE (mV)
50
(OFF-TO-ON)
ILOAD = 1mA
0.8
0.6
0.4
(ON-TO-OFF)
ILOAD = 1mA
VSHDN2 = OPEN CIRCUIT
20
15
10
VSHDN2 = 0V
(REGULATOR 2
IN SHUTDOWN)
5
0.2
0
–50 –25
50
0
75
25
TEMPERATURE (°C)
100
125
LT1239 • TPC10
0
0
1
2 3 4 5 6 7 8
INPUT 2 VOLTAGE, PIN 10 (V)
9
10
LT1239 • TPC11
5
LT1239
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PIN FUNCTIONS
ADJ (Pin 1): Adjust Pin of Regulator 1. The regulator will
servo the adjust pin to 3.75V referred to ground. Bias
current will be approximately 50nA and will flow into the
adjust pin.
E/A (IN) (Pin 7): Noninverting Input of the Error Amplifier.
This pin should be tied to the center tap point in the output
divider for regulator 1. The bias current for this pin will be
in the range of 3nA and it will flow out of the pin.
GND (Pin 2): Ground Pin for Regulator 1. Note that the
three ground pins (pins 2, 4, 5) are connected together
internally and should all be grounded externally.
E/A (OUT) (Pin 8): Output of the Error Amplifier. This is
normally connected to the center tap of the backup cells.
SHDN1 (Pin 3): Shutdown Pin for Regulator 1. Regulator
1 output will be on if the shutdown pin is either: 1) Left
floating (open circuit) or 2) pulled up to the 5V rail. If the
shutdown function is not used, the shutdown pin is normally left open circuit. Regulator 1 output will be off if the
shutdown pin is pulled to ground. The shutdown pin
current with the pin pulled to ground will be in the range of
2µA flowing out of the pin. The shutdown pin current with
the pin pulled up to 5V will be zero.
INPUT 2 (Pin 10): Input Pin (VCC) for Regulator 2, the Error
Amplifier, and the Low-Battery Detection Circuit.
GND (Pin 4): Ground. This ground pin is tied to the
substrate of the die, between regulator 1 and the rest of the
circuit. It is used as an isolation barrier between regulator
1 and the rest of the circuitry.
GND (Pin 5): Ground Pin for Regulator 2.
SHDN2 (Pin 6): Shutdown Pin for Regulator 2. Regulator
2 output will be on if the shutdown pin is either: 1) Left
floating (open circuit) or 2) pulled up to the 5V rail. If the
shutdown function is not used, the shutdown pin is normally left open circuit. Regulator 2 output will be off if the
shutdown pin is pulled to ground. The shutdown pin
current with the pin pulled to ground will be in the range of
2µA flowing out of the pin. The shutdown pin current with
the pin pulled up to 5V will be zero.
NC (Pin 9): Not Connected.
IMON 2 (Pin 11): Current Monitor Pin for Regulator 2. If the
current monitor function is not used, this pin should be
tied to the output pin of regulator 2.
OUT 2 (Pin 12): Output of Regulator 2. It is also the
inverting input and output of the comparator. If the main
5V system supply is up and running then the comparator
output will pull the output of regulator 2 up to 5V.
5VIN (Pin 13): Noninverting Input of the comparator and
the collector of the output driver. The collector of the
output driver is normally connected to the main 5V system
supply.
INPUT 1 (Pin 14): Input Pin (VCC) of Regulator 1.
IMON 1 (Pin 15): Current Monitor Pin for Regulator 1. The
current flowing out of this pin will be approximately 1/200
of the output current of regulator 1. If the current monitor
function is not used, this pin should be tied to the output
pin of regulator 1.
OUT 1 (Pin 16): Output of Regulator 1.
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FUNCTIONAL DESCRIPTIO
Regulator 1: Regulator 1 is used to supply the charging
current to the backup batteries. It converts the voltage on
the main battery to a fixed output voltage to charge the
backup cells. The output voltage is set with a voltage
divider connected between the output and ground with a
tap point of the divider connected to the adjust pin. The
regulator servos its output in order to maintain the adjust
pin at 3.75V referred to ground. The resistor divider
should be chosen such that the divider current is approxi-
6
mately 5µA. This means the impedance from the adjust pin
to ground should be approximately 750kΩ. For safety
requirements a resistor can be placed between the output
pin and the top of the divider that sets the regulated output
voltage. The regulator will regulate the voltage at the top of
the divider. Quiescent current will be 10µA to 15µA. Output
short-circuit current will be approximately 70mA.
LT1239
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FUNCTIONAL DESCRIPTIO
Comparator: The output of the comparator is connected to
the output of regulator 2. This point provides power to
memory and power management circuitry. The comparator looks at the main 5V power line and the output voltage
of regulator 2. If the main 5V line is up and regulating the
comparator output will pull up to 5V and supply power to
the memory from the main 5V regulator. If the main 5V
power line drops below 4.85V the comparator switches off
and regulator 2 will supply power to the memory from the
backup batteries. The comparator is powered from the raw
battery voltage at the input of regulator 1.
Error Amplifier: The Error Amplifier is used to equalize the
cell voltages of two lithium-ion cells connected in series.
The error amplifier is designed to source or sink 5mA.
Low-Battery Detector: The low-battery detector circuit
acts as an undervoltage lockout. This circuit turns regulator 2 and the error amplifier off if the backup battery
voltage drops below 5V. The low-battery detector circuit
will turn regulator 2 and the error amplifier back on when
the backup battery voltage rises above 5.3V. This circuit
has a quiescent current of approximately 3µA in the
undervoltage condition.
Regulator 2: Regulator 2 is used to regulate the voltage of
the backup batteries and isolate the backup batteries from
the main 5V line. This regulator will prevent reverse
current flow from the main 5V supply back into the backup
cells.
W
BLOCK DIAGRAM
–
INPUT 2 10
13 5VIN
INPUT 1
E/A (IN) 7
+
8 E/A (OUT)
E/A
+
POWER
SWITCH
COMP
IN
INPUT 1 14
16 OUT 1
REGULATOR
1
3
4 2
SHDN1 GND
1 ADJUST
LOW-BATTERY
DETECTOR
15
REGULATOR
2
6
5
SHDN2 GND
IMON1
–
IN
11
12
IMON2
OUT 2
1239 BD
GROUND PINS 2, 4, 5 ARE TIED TO SUBSTRATE
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APPLICATIONS INFORMATION
Device Overview
The LT1239 provides several functions needed for backup
battery management. It provides:
1. Battery Charging: The LT1239 can be set up to charge
lithium-ion or nickel cadmium batteries in either constant voltage or constant current mode.
2. Memory Power Control: The LT1239 provides power
for the memory and includes automatic switchover
between the backup battery and the main 5V system
power. When the 5V system supply is up and running it
is used to power the memory, the regulator prevents
reverse current flow back into the backup battery.
Automatic switchover occurs when the 5V system
supply drops below 4.85V and the regulator then provides power to the memory from the backup cells.
Memory power is uniterruptable.
7
LT1239
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APPLICATIONS INFORMATION
3. Protection: Regulator 1 allows the use of current limiting resistors to prevent overcharging lithium-ion cells.
A low-battery detector shuts down regulator 2 and the
error amplifier to prevent over discharging the lithium
cells. An error amplifier is included to provide voltage
equalization for two series connected lithium-ion cells.
Adjusting Output Voltage
Regulator 1 is an adjustable regulator. This allows the
output voltage to be set for various battery types and
voltages. The output voltage is adjustable from 3.75V up
to 20V. The regulator will servo its output voltage in order
to maintain the adjust pin at 3.75V with respect to ground.
The output voltage is set with a resistor divider from output
to ground as shown in Figure 1. The resistor values should
be chosen so that the current in the divider is approximately 5µA. This means that the impedance from the
adjust pin to ground should be approximately 750kΩ. The
bias current at the adjust pin is 50nA (typical) and will flow
into the adjust pin. The error in the output voltage, due to
the adjust pin bias current will be equal to the bias current
multiplied by the value of R2 ( IADJ × R2). This error is small
and is compensated for in the formulas shown in Figure 1.
Equalizing Lithium-Ion Cells
The error amplifier on the LT1239 is used to equalize the
cell voltages in a 2-cell lithium-ion backup system. The
error amplifier is internally connected as a unity-gain
follower and is designed to sink or source about 3mA. The
bias current for the error amplifier will be approximately
3nA and will flow out of the pin. The output voltage of the
error amplifier can be set by connecting the input to a tap
point on the resistor divider used to set the output voltage
for regulator 1 as shown in Figure 2. The error amplifier
will then equalize the cell voltages by charging the cell with
the lowest output voltage. The output voltage of regulator
1 controls the total cell voltage and the error amplifier
forces the cell voltages to be equal. The error amplifier
output current will go to zero when the cell voltages are
equal and the total cell voltage is equal to the output
voltage of regulator 1.
6.8V
IN 1
OUT 1
ADJ
OUT 1
R3
69.8k
5µA
(VOUT – 3.75V)
(3.75V/R1) + IADJ
CHOOSE: R1 = 750k
IADJ = 50nA
LT1239 • F01
Figure 1. Adjusting Output Voltage
Example: To set the output voltage to 6.8V for a 2-cell
lithium-ion system, use R1 = 750k and IADJ = 50nA.
R2 =
8
+
Figure 2. Equalizing Lithium-Ion Cells
R1 ≈ 750k
)
Then:
6.8V – 3.75V
= 604k
(3.75V/750k) + 50nA
E/A (OUT)
LT1239 • F02
VOUT = 3.75 1 + R2 + IADJ (R2)
R1
R2 =
E/A
E/A (IN)
50nA
ADJ
)
–
R1
681k
R2
REGULATOR 1
10µF
3.75V
3.4V
IN 1
+
R2 = 604k
REGULATOR 1
For battery voltages greater than the low-battery detection
threshold the error amplifier is active. For battery voltages
lower than the low-battery detection threshold the output
of the error amplifier is inactive. When the error amplifier
is active it can source or sink approximately 3mA. When
the error amplifier is inactive its output is a high impedance, as long as it is not forced above VIN2 or below
ground.
The error amplifier is powered from the same supply pin
as regulator 2. In most applications the backup batteries
and the output of regulator 1 will provide power to this
point. This means that the protection resistors (R4 in
Figure 5) in series with the output of regulator 2 will limit
the output current capability of the error amplifier in a
fault condition.
LT1239
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APPLICATIONS INFORMATION
Using the Current Monitor Function
The current monitor pin outputs a current proportional to
the output current of the regulator. Both regulator 1 and
regulator 2 have independent current monitor pins. The
current monitor function can be used to monitor charge in
the backup cells, to set up a constant current output or to
adjust the current limit of the regulator. The current
monitor pin should be tied to the output pin if the current
monitor function is not used. This will minimize quiescent
current.
The current output of the current monitor pin can be
converted to a voltage by feeding the current monitor pin
output current through a resistor. The voltage across the
resistor will be proportional to output current. This signal
can be used to monitor the output current for either
regulator. Regulator 1 output current is equal to the charge
current for the backup batteries plus the load current of
regulator 2. If regulator 1 output current is greater than
regulator 2 output current, the difference between the
currents is the charge current for the backup cells. If
regulator 2 output current is greater than regulator 1
output current, the difference between the currents is the
discharge current for the backup cells. By integrating the
difference between regulator 1 output current and regulator 2 output current the total charge in the backup cells can
be determined.
Constant Current Charging
using regulator 1 and the circuit shown in Figure 3.
In this circuit the voltage at the adjust pin is proportional
to the output current. Regulator 1 will servo its output to
force 3.75V at the adjust pin. The output current will be
scaled from the current monitor pin current by a ratio of
220:1. Output current is equal to 220 × current monitor pin
current. The output current is set by choosing resistor R1,
in the formula shown in Figure 3. Regulator 1 will source
a constant current as long as the voltage at its input is
greater than the battery voltage plus the dropout voltage of
regulator 1. External power monitoring circuitry can be
used to shutdown regulator 1 to terminate charge when a
low current sleep mode is desired.
Setting Current Limit Using the Current Monitor Pin
With the addition of some simple external circuitry the
current monitor pin can be used to control the output
short-circuit current of the regulator. As shown in Figure
4, the current monitor pin can be tied to ground through
a resistor to generate a voltage proportional to output
current. When the voltage across R3 is equal to approximately 0.6V (one VBE) Q1 will turn on and pull down on the
shutdown pin of the regulator. Q1 effectively steals drive
current from the regulator to limit the output current. C1
is needed to roll off the gain of Q1. Current limit can be set
using the formula shown in Figure 4. This circuit can be
used with either regulator. The shutdown function can
also be used. An open-collector gate connected in parallel
with Q1 can shut down the regulator.
NiCd backup batteries are normally charged with a constant current trickle charge. This can be accomplished
IN 1
R2
ICHARGE
7-24V
+
IN 1
OUT 1
LT1239
LT1239 IMON1
ADJ
MAIN
BATTERIES
+
10µF
SHDN1 GND
NiCd
BACKUP
BATTERY
Q1
ICHARGE
OFF
> 2.8V
ON
NC
ON
10µF
ADJ
NiCd
BACKUP
BATTERY
R1
IMON1
R1 =
2N3904
+
3.75V
ICHARGE
× 220
Figure 3. Constant Current Charging
+
R3
2µF
R3 =
< 0.25V
SHDN2 GND
+
(3.75V)
R1
VSHDN1
OUT 1
+
0.6V
× 220
ILIM
C1
2µF
LT1239 • F04
Figure 4. Reducing Current Limit
Using the Comparator
LT1239 • F03
The comparator in the LT1239 is intended to be used as an
automatic switchover circuit between the main 5V
9
LT1239
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APPLICATIONS INFORMATION
system power and the backup batteries. The comparator
output will be driven high if the output of the 5V system
supply is greater than the 4.85V output of regulator 2.
Regulator 2 will act as a diode to prevent current flow from
the 5V system supply back into the backup battery. Current flow into the output of regulator 2, with the output
pulled up to 5V, will be limited to approximately 6µA and
will flow to ground. If the main 5V system supply drops
below the 4.85V output of regulator 2 the comparator will
switch off and regulator 2 will provide power to the
memory. The comparator combined with regulator 2 and
the batteries provide an uninterruptable power source to
the memory and power monitoring circuitry.
Choosing Current Limiting Resistors
Due to UL safety considerations, circuits used to charge
lithium-ion batteries must have external resistors (passive
components) to limit the available charge current in the
event of a failure in the charging circuit. The LT1239 allows
these resistors to be placed in series with the output
transistor of the regulator 1 as shown in Figure 5. The
current limiting resistor (R4) will be in series with the main
charge current path but will be inside the feedback loop of
regulator 1. Because the resistors are inside the feedback
loop they will not affect output voltage regulation in
normal operating conditions. The resistors should be
selected so that they limit the charge current below the
maximum level specified by the battery manufacturer. For
a typical 3.4V, 50mA rechargeable backup cell (Panasonic
VL2330) the maximum charge current is specified at
300mA. Most users will choose to limit the current well
below the maximum charge current. It is important to note
that these resistors can also limit the charge current
during normal operation. Since the charge current for a
typical lithium-ion button cell is normally less than 20mA,
limited by the internal impedance of the cells during a
constant voltage charge, the current limiting resistors do
not significantly affect the charge times for the backup
cells. The worst case would occur if the regulator failed as
a short and the main battery is at its maximum charge
voltage. The current limiting resistor (R4) must be chosen
to limit the current to less than the manufacturers maximum charging current with the difference between the
main battery voltage and the backup battery voltage dropped
across it.
10
For example with a main battery voltage of 24V max, a
backup battery voltage of 6.8V and a maximum charge
current of 300mA, R4 must be greater than (24V – 6.8V) /
300mA, R4 > 57Ω.
R4 can also be used to limit the power dissipated by
regulator 1 as shown in the following section. C1 is needed
for stability in circuits with protection resistors (R4).
The power dissipation in R4 during fault conditons can be
significant. it will be equal to:
(VINL – VBATTERY)2
R4
Power resistors with ratings greater than 0.25W or fusable
resistors may be required.
Thermal Considerations
The power dissipation of this device is made up of several
components.They are the power dissipation of each regulator, the comparator and the error amplifier. The largest
component will be due to the power in regulator 1, when
the charge current for the batteries is the highest and the
input voltage to regulator 1 is at the maximum. In most
systems this condition only occurs for a short period after
the backup battery has been completely discharged. Both
regulators have thermal limiting circuitry which limits the
power in the regulator when the junction temperature
reaches about 100°C. The thermal limit temperature is set
low because the device is designed to work with batteries
specified to run at ambient temperatures below 60°C. The
power in regulator 1 can be limited with external resistors
placed in the feedback loop as shown in Figure 5. In
lithium-ion systems these resistors are required for safety
reasons.
The power in regulator 1 will be equal to:
[(VMAINBATTERY – VBACKUPBATTERY) × ICHG] – (ICHG × R4)
Note that for circuits with a current limiting resistor (R4)
the worst-case power point occurs when ICHG is equal to
the maximum charging current/2.
Example: [(24V – 6.8V) × (71mA/2)] – [(71mA/2) × 240]
= 300mW
This is the only significant component of power dissipation
in the device and this condition will only occur when the
LT1239
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APPLICATIONS INFORMATION
backup batteries have been completely discharged. Once the
backup batteries are charged the power in regulator 1 drops
significantly. The power in regulator 2 when regulator 2 is
providing power to the memory will be equal to:
(VBACKUPBATTERY – 4.85V) × IOUT
(VBACKUPBATTERY/2) × 3mA
Example: (6.8V/2) × 3mA = 10.2mW
IOUT is the current needed to power the memory and power
monitoring circuitry.
Example: (6.8V – 4.85V) × 30mA = 58.5mW
The power in the comparator when the comparator is providing power to the memory will be equal to:
(VSAT × IOUT)
IOUT is the current needed to power the memory and power
monitoring circuitry. Comparator Output Saturation Voltage
vs Output Current can be found in the Typical Performance
Characteristics.
Example: (VSAT × ILOAD) = (0.15V × 30mA) = 4.5mW
V1
This component goes to zero when the cell voltages are
equalized.
The thermal resistance of the LT1239 is 120°C/W when
the device is mounted to a PC board with at least one
ground or power plane. The junction temperature rise will
be equal to the total power in the device multiplied by
120°C/W or (PTOTAL × 120°C/W). For 300mW dissipation
the junction temperature rise will be (300mW × 120°C/W)
= 36°C. Given that the thermal limit temperature is approximately 100°C, this allows for a maximum ambient
temperature of roughly 60°C before the device thermal
limits. This temperature is near the maximum ambient
allowed for most battery types.
*R4
IN 1
MAIN
BATTERY
PACK
Note that power for memory will be supplied by either
regulator 2 or the comparator. The power in the error
amplifier when the cells are unequalized will be equal to:
V2
OUT 1
+
IMON1
LT1239
C1
300pF
R3
604k
+
10µF
3.4V Li-Ion
CELL
ADJ
R2
69.8k
E/A (IN)
E/A (0UT)
R1
681k
3.4V Li-Ion
CELL
GND
R4 >
V1 – V2
MAX CHARGE CURRENT
*THIS RESISTOR IS REQUIRED
BY SOME SAFETY AGENCIES.
LT1239 • F05
Figure 5. Adding a Protection Resistor for Lithium-Ion Charger
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.
11
LT1239
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TYPICAL APPLICATIONS
NiCd Backup System with 20mA Charge Current
NiCd Backup System with 5mA Trickle Charge
50Ω
OUT 1
IN 1
650k
+
MAIN
BATTERY
PACK
ADJ
5µF
6V NiCd
BACKUP
BATTERY
10µF
IMON1
SHDN1
IN2
SHDN2
750k
LT1239
E/A (IN)
+
MAIN
BATTERY
PACK
SHDN1
IN2
E/A (0UT)
GND
IMON2
IMON1
LT1239
E/A (IN)
SHDN2
+
MEMORY
10µF
5V POWER
SYSTEM
POWER
MONITORING
CIRCUITRY
1µF
E/A (0UT)
OUT 2
5V POWER
SYSTEM
10µF
+
165k
+
10µF
+
NiCd
BACKUP
BATTERIES
ADJ
5µF
OUT2
5VIN
OUT 1
IN 1
+
5VIN
GND
IMON2
MEMORY
POWER
MONITORING
CIRCUITRY
LT1239 • TA03
LT1239 • TA02
U
PACKAGE DESCRIPTION
Dimension in inches (millimeters) unless otherwise noted.
S Package
16-Lead Plastic DIP
0.386 – 0.394*
(9.804 – 10.008)
16
15
14
13
12
11
10
9
0.150 – 0.157*
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
2
3
4
5
6
7
8
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0° – 8° TYP
0.016 – 0.050
0.406 – 1.270
0.014 – 0.019
(0.355 – 0.483)
0.050
(1.270)
TYP
SO16 0893
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
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DESCRIPTION
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12
Linear Technology Corporation
LT/GP 0695 10K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
 LINEAR TECHNOLOGY CORPORATION 1995