LTC3533 datasheet(6/16 Pages) LINER

6 / 16 page

LTC3533

3533f

PIN FUNCTIONS

RT (Pin 1): Programs the Frequency of the Internal Oscil-

lator. Connect a resistor from RT to ground.

f(kHz) = 33,170/RT (kΩ)

BURST (Pin 2): Used to set the Automatic Burst Mode

Threshold. Connect a resistor and capacitor in parallel

from this pin to ground. See the Applications Information

section for component value selection. For manual control,

ground the pin to force Burst Mode operation, connect to

VIN to force ﬁxed frequency PWM mode.

SGND (Pin 3): Signal ground for the IC.

SW1 (Pin 4): Switch Pin where Internal Switches A and B

are Connected. Connect inductor from SW1 to SW2. An

optional Schottky diode can be connected from SW1 to

ground for a moderate efﬁciency improvement. Minimize

trace length to reduce EMI.

PGND1, PGND2 (Pins 5, 6): Power Ground for the Internal

NMOS Power Switches.

SW2 (Pin 7): Switch Pin where Internal Switches C and

D are Connected. An optional Schottky diode can be

connected from SW2 to VOUT for a moderate efﬁciency

improvement. For applications with output voltages over

4.3V, this Schottky diode is required to ensure the SW2

pin does not exhibit excess voltage. Minimize trace length

to reduce EMI.

VOUT (Pin 8): Voltage Sensing Pin for PVOUT and Input

Supply Pin for Internal Circuitry Powered by PVOUT. A ﬁlter

capacitor is placed from VOUT to GND. A ceramic bypass

capacitor is recommended as close to the VOUT and GND

pins as possible.

PVOUT (Pin 9): Output of the Synchronous Rectiﬁer. A

ﬁlter capacitor is placed from PVOUT to PGND. A ceramic

bypass capacitor is recommended as close to the PVOUT

and PGND pins as possible.

VIN (Pin 10): Input Supply Pin. Internal VCC for the IC.

PVIN (Pin 11): Power VIN Supply Pin. A 10µF ceramic

capacitor is recommended as close to the PVIN and PGND

pins as possible.

RUN/SS (Pin 12): Combined Enable and Soft-Start. Applied

voltage <0.4V shuts down the IC. Tie to >1.4V to enable

the IC and >1.6V to ensure the error amp is not clamped

from soft-start. An RC from the shutdown command signal

to this pin will provide a soft-start function by limiting the

rise time of VC

FB (Pin 13): Feedback Pin. Connect resistor divider tap

here. The output voltage can be adjusted from 1.8V to

5.25V. The feedback reference voltage is typically 1.22V.

OUT =

122

.•

VC (Pin 14): Error Amp Output. An R-C network is con-

nected from this pin to FB for loop compensation. Refer

to “Closing the Feedback Loop” section for component

selection guidelines. During Burst Mode operation, VC is

internally connected to a hold circuit.

Exposed Pad (Pin 15): IC Substrate Ground. This pin must

be soldered to the PCB ground to provide both electrical

contact and a good thermal contact to the PCB.

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