LT1239 데이터 시트보기 (PDF) - Linear Technology
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LT1239 Datasheet PDF : 12 Pages
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LT1239
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 compara-
tor 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 regula-
tor 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.
BLOCK DIAGRAM
INPUT 2 10
E/A (IN) 7
–
E/A
+
8 E/A (OUT)
INPUT 1 14
REGULATOR
1
16 OUT 1
1 ADJUST
IN
LOW-BATTERY
DETECTOR
IN
REGULATOR
2
3 4 2 15
SHDN1 GND IMON1
6
5 11
SHDN2 GND IMON2
GROUND PINS 2, 4, 5 ARE TIED TO SUBSTRATE
INPUT 1
+
COMP
–
13 5VIN
POWER
SWITCH
12
OUT 2 1239 BD
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 con-
stant 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 pro-
vides power to the memory from the backup cells.
Memory power is uniterruptable.
7
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