LT8610AC datasheet(13/32 Pages) AD

13 / 32 page

LT8636/LT8637

Rev. C

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TR/SS (Pin 18): Output Tracking and Soft-Start Pin. This

pin allows user control of output voltage ramp rate dur-

ing start-up. For the LT8636/LT8637, a TR/SS voltage

below 0.97V forces it to regulate the FB pin to equal the

TR/SS pin voltage. When TR/SS is above 0.97V, the

tracking function is disabled and the internal reference

resumes control of the error amplifier. For the LT8637,

a TR/SS voltage below 1.6V forces it to regulate the FB

pin to a function of the TR/SS pin voltage. See plot in

the Typical Performance Characteristics section. When

TR/SS is above 1.6V, the tracking function is disabled

and the internal reference resumes control of the error

amplifier. An internal 1.9µA 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 tracking function is not

needed.

FB (Pin 19, LT8636 Only): The LT8636/LT8637 regu-

lates the FB pin to 0.970V. Connect the feedback resistor

divider tap to this pin. Also, connect a phase lead capaci-

tor between FB and VOUT. Typically, this capacitor is 4.7pF

to 22pF.

VC (Pin 19, LT8637 Only): 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.

FB (Pin 20): The LT8636/LT8637 regulates the FB pin to

0.970V. 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 22pF.

Corner Pins: These pins are for mechanical support only

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

PIN FUNCTIONS

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