1

LT1579

300mA Dual Input Smart

Battery Backup Regulator

Daisy-Chained Control Outputs

FEATURES

The LT

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 50

µA, 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.

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Maintains Output Regulation with Dual Inputs

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Dropout Voltage: 0.4V

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Output Current: 300mA

s

50

µA Quiescent Current

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No Protection Diodes Needed

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Two Low-Battery Comparators

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Status Flags Aid Power Management

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Adjustable Output from 1.5V to 20V

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Fixed Output Voltages: 3V, 3.3V and 5V

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7

µA Quiescent Current in Shutdown

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Reverse-Battery Protection

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Reverse Current Protection

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Remove, Recharge and Replace Batteries Without

Loss of Regulation

5V Dual Battery Supply

Automatic Input Switching

2.7M

1M

2.7M

1M

+

1

µF

+

1

µF

+

4.7

µF

5V

300mA

TO

POWER

MANAGEMENT

0.01

µF

IN1

OUT

SS

SHDN

LBO1

LB02

BACKUP

DROPOUT

BIASCOMP

LBI1

IN2

LBI2

GND

LT1579-5

1579 TA01

TIME (ms)

0

4

8

12

16

1578 TA02

0

5.00

2

6

40

80

0

20

60

10

5.05

4.95

4

8

12

218

6

10

14

20

SWITCHOVER

POINT

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Dual Battery Systems

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Battery Backup Systems

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Automatic Power Management for

Battery-Operated Systems

, LTC and LT are registered trademarks of Linear Technology Corporation.