LTC3539/LTC3539-2

6

3539f

BLOCK DIAGRAM

PIN FUNCTIONS

SW (Pin 1): Switch Pin. Connect inductor between SW

sible to reduce EMI. If the inductor current falls to zero,

or SHDN is low, an internal anti-ring resistor is connected

PGND (Pin 2), GND (Pin 3): Signal and Power Ground.

Provide a short direct PCB path between PGND, GND and

the (–) side of the input and output capacitors.

of 2.2μF ceramic decoupling capacitor from this pin to

ground.

SHDN (Pin 5): Logic Controlled Shutdown Input. There

is an internal 4MΩ pull-down on this pin.

SHDN = High: Normal operation.

SHDN = Low: Shutdown, quiescent current <1μA.

nect resistor divider tap to this pin. The output voltage

[1 + (R2/R1)]

MODE (Pin 7): Burst Mode Pin. A logic controlled input

to select either automatic Burst Mode operation or forced

fixed frequency operation.

MODE = High: Burst Mode operation at light loads

MODE = Low: Fixed frequency PWM Mode

Internal Synchronous Rectifier. PCB trace length from

wide as possible.

Exposed Pad (Pin 9): The exposed pad must be soldered

to the PCB ground plane. It serves as another ground

connection, and as a means of conducting heat away

from the die.

3539 BD

SW

SHDN

EXPOSED PAD

WAKE

BURST

SOFT-START

ERROR

AMPLIFIER/SLEEP

COMPARATOR

COMPARATOR

COMPARATOR

SLOPE

COMPARATOR

GND

MODE

FB

FB

R2

LOGIC AND

BURST MODE

CONTROL

GATE DRIVERS

AND

ANTI-CROSS

CONDUCTION

THERMAL

SHUTDOWN

START-UP

CLAMP

SHUTDOWN

SHUTDOWN

UVLO

UVLO

TSD

WELL

SWITCH

R1

1MHz/2MHz

OSC

CLK

BURST

PWM

ON

OFF

1

4

8

6

3

PGND

2

9

7

5