LT8610AB datasheet(12/28 Pages) AD

12 / 28 page

LT8638S

Rev. 0

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PG (Pin 25): The PG pin is the open-drain output of an

internal comparator. PG remains low until the FB pin is

within ±7.75% of the final regulation voltage, and there

are no fault conditions. PG is also pulled low when EN/

UV is below 1V, INTVCC has fallen too low, VIN is too low,

or thermal shutdown. PG is valid when VIN is above 2.8V.

VC (Pin 26): The VC pin is the output of the internal error

amplifier. The voltage on this pin controls the peak switch

current. Tie an RC network from this pin to ground to

compensate the control loop.

SS (Pin 27): Output Tracking and Soft-Start Pin. This pin

allows user control of output voltage ramp rate during

start-up. A SS voltage below 1V forces the LT8638S to

regulate the FB pin to a function of the SS pin voltage. See

plot in the Typical Performance Characteristics section.

When SS is above 1V, the tracking function is disabled

and the internal reference resumes control of the error

amplifier. An internal 2µA pull-up current from INTVCC

on this pin allows a capacitor to program output voltage

slew rate. This pin is pulled to ground with an internal

200Ω MOSFET during shutdown and fault conditions; use

a series resistor if driving from a low impedance output.

This pin may be left floating if the soft-start feature is not

being used.

FB (Pin 28): The LT8638S regulates the FB pin to 0.6V.

Connect the feedback resistor divider tap to this pin. Also,

connect a phase lead capacitor between FB and VOUT.

Typically, this capacitor is 4.7pF to 47pF.

Corner Pins: These pins are for mechanical support only

and can be tied anywhere on the PCB, typically ground.

PIN FUNCTIONS

LT8610AB Datasheet(PDF) 12 Page - Analog Devices