1308AI datasheet(6/20 Pages) LINER

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LT1308A/LT1308B

1308abfa

VC (Pin 1/Pin 1): Compensation Pin for Error Amplifier.

Connect a series RC from this pin to ground. Typical

values are 47k

Ω and 100pF. Minimize trace area at VC.

FB (Pin 2/Pin 2): Feedback Pin. Reference voltage is

1.22V. Connect resistive divider tap here. Minimize trace

area at FB. Set VOUT according to:

VOUT = 1.22V(1 + R1/R2).

SHDN (Pin 3/Pin 3): Shutdown. Ground this pin to turn

off switcher. To enable, tie to 1V or more. SHDN does not

need to be at VIN to enable the device.

GND (Pin 4/Pins 4, 5, 6, 7): Ground. Connect directly to

local ground plane. Ground plane should enclose all

components associated with the LT1308. PCB copper

connected to these pins also functions as a heat sink. For

the TSSOP package, connect all pins to ground copper to

get the best heat transfer. This keeps chip heating to a

minimum.

PIN FUNCTIONS (SO/TSSOP)

SW (Pin 5/Pins 8, 9, 10): Switch Pins. Connect inductor/

diode here. Minimize trace area at these pins to keep EMI

down. For the TSSOP package, connect all SW pins

together at the package.

VIN (Pin 6/Pins 11, 12): Supply Pins. Must have local

bypass capacitor right at the pins, connected directly to

ground. For the TSSOP package, connect both VIN pins

together at the package.

LBI (Pin 7/Pin 13): Low-Battery Detector Input. 200mV

reference. Voltage on LBI must stay between –100mV

and 1V. Low-battery detector does not function with

SHDN pin grounded. Float LBI pin if not used.

LBO (Pin 8/Pin 14): Low-Battery Detector Output. Open

collector, can sink 50

μA. A 220kΩ pull-up is recom-

mended. LBO is high impedance when SHDN is grounded.

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