LT1579_15 Datasheet, PDF (1/20 Pages) Linear Technology – 300mA Dual Input Smart Battery Backup Regulator

FEATURES
s _{Maintains Output Regulation with Dual Inputs}
s _{Dropout Voltage: 0.4V}
s _{Output Current: 300mA}
s _{50µA Quiescent Current}
s _{No Protection Diodes Needed}
s _{Two Low-Battery Comparators}
s _{Status Flags Aid Power Management}
s _{Adjustable Output from 1.5V to 20V}
s _{Fixed Output Voltages: 3V, 3.3V and 5V}
s _{7µA Quiescent Current in Shutdown}
s _{Reverse-Battery Protection}
s _{Reverse Current Protection}
s _{Remove, Recharge and Replace Batteries Without}
Loss of Regulation^{Daisy-Chained Control Outputs}
U
APPLICATIONS
s _{Dual Battery Systems}
s _{Battery Backup Systems}
s _{Automatic Power Management for}
Battery-Operated Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
5V Dual Battery Supply
IN1
OUT
+
1µF ^2.7M
LBI1
1M
LT1579-5
+
IN2
1µF ^2.7M
LBI2
1M
SS
SHDN
LBO1
LB02
BACKUP
DROPOUT
BIASCOMP
GND
5V
+
300mA
4.7µF
TO
POWER
MANAGEMENT
0.01µF
1579 TA01
LT1579
300mA Dual Input Smart
Battery Backup Regulator
DESCRIPTION
The LT^®1579 is a dual input, single output, low dropout
regulator. This device is designed to provide an
uninterruptible output voltage from two independent input
voltage sources on a priority basis. All of the circuitry
needed to switch smoothly and automatically between
inputs is incorporated.
The LT1579 can supply 300mA of output current from
either input at a dropout voltage of 0.4V. Quiescent current
is 50µA, dropping to 7µA in shutdown. Two comparators
are included to monitor input voltage status. Two addi-
tional status flags indicate which input is supplying power
and provide an early warning against loss of output
regulation when both inputs are low. A secondary select
pin is provided so that the user can force the device to
switch from the primary input to the secondary input.
Internal protection circuitry includes reverse-battery pro-
tection, current limiting, thermal limiting and reverse-
current protection.
The device is available in fixed output voltages of 3V, 3.3V
and 5V, and as an adjustable device with a 1.5V reference
voltage. The LT1579 regulators are available in narrow
16-lead SO and 16-lead SSOP packages with all features,
and in SO-8 with limited features.
Automatic Input Switching
12
10 V_{IN1 SWITCHOVER}
8
POINT
V_IN2 = 10V
I_LOAD = 50mA
80
6 I_IN1
I_IN2
60
4
40
2
20
0
0
5.05
5.00
4.95
0 2 4 6 8 10 12 14 16 18 20
TIME (ms)
1578 TA02
1