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LT1680

High Power DC/DC Step-Up Controller

Linear Technology 

LT1680

PIN FUNCTIONS

RUN/SHDN (Pin 11): Precision Referenced Shutdown.

Can be used as logic level input for shutdown control or as

an analog monitor for input supply undervoltage protec-

tion, etc. IC is enabled when RUN/SHDN pin rising edge

exceeds 1.25V. 15mV of hysteresis helps assure stable

mode switching. All internal functions are disabled in

shutdown mode. If this function is not desired, connect

RUN/SHDN to 12VIN (typically through a 100k resistor).

See Applications Information.

PGND (Pin 12): Power Ground. References the output

switch and internal driver control circuits. Connect with

low impedance trace to VIN decoupling capacitor negative

(ground) terminal.

GATE (Pin 13): Driver Output. Connect to gate of external

power FET switch.

12VIN (Pin 14): 12V Power Supply Input. Bypass with at

least 1µF to PGND.

SYNC (Pin 15): Oscillator Synchronization Pin with

TTL-Level Compatible Input. Input drives internal rising

edge triggered one shot; SYNC signal on/off times should

be ≥1µs (10% to 90% duty cycle at 100kHz). Does not

contain internal pull-up. Connect to SGND if not used.

5VREF (Pin 16): 5V Reference Output. Allows connection

of external loads up to 10mA DC. Reference is not available

during shutdown. Typically bypassed with at least 1µF

capacitor to SGND.

BLOCK DIAGRAM

RCT

CCT

SYNC

5VREF

REFERENCE

5V

1.25V

CT

ONE SHOT

–

OSC

Q

SR

GATE

UVLO

CIRCUIT

SL /ADJ

VOUT

RUN SHDN

VC

CURRENT

SENSE

VREF

AMPLIFIER

+

EA

VFB

–

SS 0.5µA

1.25V

–

RUN/SHDN +

CIRCUIT

ENABLE

+

IC1

–

SENSE +

×15 SENSE –

IAVG

2.5V

12VIN

10µA

SOFT START PGND

SGND

1680 BD

VIN

RSENSE

+

VOUT

12V

7

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