LTC7813 datasheet(8/32 Pages) LINER

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LTC7800

7800f

For more information www.linear.com/LTC7800

PIN FUNCTIONS

PLLIN/MODE (Pin 1): External Synchronization Input to

Phase Detector and Forced Continuous Mode Input. When

an external clock is applied to this pin, the phase-locked

loop will force the rising TG signal to be synchronized with

the rising edge of the external clock, and the regulator

operates in forced continuous mode. When not synchro-

nizing to an external clock, this input determines how the

LTC7800 operates at light loads. Pulling this pin to ground

selects Burst Mode operation. An internal 100k resistor to

ground also invokes Burst Mode operation when the pin is

floated.TyingthispintoINTVCCforcescontinuousinductor

current operation. Tying this pin to a voltage greater than

1.2V and less than INTVCC –1.3V selects pulse-skipping

operation. This can be done by connecting a 100k resistor

from this pin to INTVCC.

SGND (Pins 2, 3, Exposed Pad Pin 21): Small-signal

ground, must be routed separately from high current

grounds to the common (–) terminals of the CIN capacitor.

Pins 2, 3, Exposed Pad Pin 21, must both be electrically

connected to small signal ground for proper operation.

The exposed pad must be soldered to PCB ground for

rated thermal performance.

RUN (Pin 4): Digital Run Control Input. Forcing this pin

below 1.16V shuts down the controller. Forcing this pin

below 0.7V shuts down the entire LTC7800, reducing

quiescent current to approximately 14µA.

SENSE– (Pin 5): The (–) Input to the Differential Current

Comparator.WhengreaterthanINTVCC–0.5V,theSENSE–

pin supplies power to the current comparator.

SENSE+ (Pin 6): The (+) input to the differential current

comparator is normally connected to DCR sensing net-

work or current sensing resistor. The ITH pin voltage and

controlled offsets between the SENSE– and SENSE+ pins

in conjunction with RSENSE set the current trip threshold.

VFB (Pin 7): Receives the remotely sensed feedback volt-

age from an external resistive divider across the output.

ITH(Pin8):ErrorAmplifierOutputsandSwitchingRegula-

torCompensationPoint.Thecurrentcomparatortrippoint

increases with this control voltage.

INPUT VOLTAGE (V)

7800 G25

FREQ = GND

935

936

937

938

939

941

942

943

944

945

TEMPERATURE (°C)

–75

3.7

3.8

3.9

4.1

–25

75 100

7800 G26

3.6

4.2

4.0

–50

0 25 50

125 150

FALLING

RISING

TEMPERATURE (°C)

25 50 75 100 125 150

–25

–75 –50

7800 G27

VIN = 12V

Oscillator Frequency vs Input

Voltage

Undervoltage Lockout Threshold

vs Temperature

Shutdown Current vs Temperature

TYPICAL PERFORMANCE CHARACTERISTICS

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