LTC3633 datasheet(9/28 Pages) LINER

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LTC3633

3633f

PIN FUNCTIONS

V2P5 (Pin 18/Pin 21): 2.5V Regulator Output. Outputs a

regulated 2.5V supply voltage capable of supplying 10mA.

Bypass this pin with a minimum of 1μF low ESR ceramic

capacitor. Tie this pin to INTVCC when this output is not

being used in the application.

INTVCC (Pin 19/Pin 22): Internal 3.3V Regulator Output.

The internal power drivers and control circuits are powered

from this voltage. Decouple this pin to power ground with

a minimum of 1μF low ESR ceramic capacitor.

BOOST1 (Pin 20/Pin 23): Boosted Floating Driver Supply

for Channel 1. The (+) terminal of the bootstrap capacitor

connects to this pin while the (–) terminal connects to

the SW pin. The normal operation voltage swing of this

pin ranges from a diode voltage drop below INTVCC up

to VIN + INTVCC.

VIN1 (Pins 21,22/Pins 24, 25): Power Supply Input for

Channel 1. Input voltage to the on chip power MOSFETs

on channel 1. The internal LDO for INTVCC is powered off

of this pin.

SW1 (Pins 23,24/Pins 26, 27): Channel 1 Switch Node

Connection to External Inductor. Voltage swing of SW is

from a diode voltage drop below ground to VIN.

VON1 (Pin 25/Pin 28): On-Time Voltage Input for Chan-

nel 1. This pin sets the voltage trip point for the on-time

comparator. Tying this pin to the regulated output volt-

age makes the on-time proportional to VOUT1 when

VOUT1 < 6V. When VOUT1 > 6V, switching frequency may

become higher than the set frequency. The pin impedance

is nominally 180kΩ.

ITH1 (Pin 26/Pin 1): Channel 1 Error Ampliﬁer Output and

Switching Regulator Compensation Pin. Connect this pin

to appropriate external components to compensate the

regulator loop frequency response. Connect this pin to

INTVCC to use the default internal compensation.

TRACKSS1 (Pin 27/Pin 2): Output Tracking and Soft-Start

Input Pin for Channel 1. Forcing a voltage below 0.6V on

this pin bypasses the internal reference input to the error

ampliﬁer. The LTC3633 will servo the FB pin to the TRACK

voltage. Above 0.6V, the tracking function stops and the

internal reference resumes control of the error ampliﬁer.

An internal 1.4μA pull up current from INTVCC allows a

soft-start function to be implemented by connecting a

capacitor between this pin and SGND.

VFB1 (Pin 28/Pin 3): Channel 1 Output Feedback Voltage

Pin. Input to the error ampliﬁer that compares the feedback

voltage to the internal 0.6V reference voltage. Connect this

pin to a resistor divider network to program the desired

output voltage.

PGND (Exposed Pad Pin 29/Exposed Pad Pin 29): Power

Ground Pin. The (–) terminal of the input bypass capaci-

tor, CIN, and the (–) terminal of the output capacitor, COUT,

should be tied to this pin with a low impedance connec-

tion. This pin must be soldered to the PCB to provide low

impedance electrical contact to power ground and good

thermal contact to the PCB.

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