LTC3602 datasheet(9/28 Pages) LINER

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LTC3633A-2/LTC3633A-3

3633a23f

(QFN/TSSOP)

PIN FUNCTIONS

BOOST2 (Pin 17/Pin 20): Boosted Floating Driver Supply

for Channel 2. 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 PVIN+INTVCC.

INTVCC (Pin 18/Pin 21): Internal 3.3V Regulator Output.

The internal power drivers and control circuits are powered

from this voltage. The internal regulator is disabled when

both channel 1 and channel 2 are disabled with the RUN1/

RUN2 inputs. Decouple this pin to power ground with a

minimum of 1μF low ESR ceramic capacitor.

BOOST1 (Pin 19/Pin 22): 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 PVIN + INTVCC.

SVIN (Pin 20/Pin 23): Signal Input Supply. This pin powers

the internal control circuitry. The internal LDO for INTVCC

is powered from this pin.

PVIN1 (Pins 21, 22/Pins 24, 25): Power Supply Input for

Channel 1. Input voltage to the on chip power MOSFETs

on channel 1.

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 PVIN.

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 voltage

makes the on-time proportional to VOUT1 when VOUT1 is

within the VON1 sense range (0.6V – 6V for LTC3633A-2,

1.5V – 12V for LTC3633A-3). When VOUT is outside the

VON sense range, the switching frequency may deviate

from the programmed frequency. The pin impedance is

nominally 140kΩ.

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 LTC3633A-2 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 connect-

ing 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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