LTC3306

7

Rev. 0

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PIN FUNCTIONS

PGOOD (A1): PGOOD is the open-drain output of an inter-

nal power good comparator. When the regulated output

voltage falls below the PGOOD threshold or rises above

the overvoltage threshold, PGOOD is pulled low. When

VIN is above 2.25V and the part is in shutdown, this pin

is also pulled low.

GND (A2): GND is the output voltage remote ground sense

and the return path of the internal bottom side power

switch. Connect the negative terminals of the input and

output capacitors as close to the IC as possible.

EN (B1): EN has a precision enable threshold with hyster-

esis. An external resistor divider, from VIN or from another

supply, can be used to program the threshold below which

the LTC3306 will shut down. If the precision threshold is

not required, tie EN directly to VIN. When the EN pin is low,

the LTC3306 enters a low current shutdown mode where

all internal circuitry is disabled. Do not float this pin.

SW (B2): SW is the switching output of the internal

power switches. Connect SW to the inductor with a short,

wide trace.

FB (C1): FB is the output voltage feedback pin for the

LTC3306 adjustable version. The FB pin is regulated to

500mV. Connect an external resistor divider on this pin

to set the output voltage.

VOUT (C1): VOUT is the regulated output voltage pin for

the LTC3306 fixed voltage versions. Connect a low-ESR

capacitor from this node to GND.

VIN (C2): VIN supplies current to the internal circuitry and

topside power switch. Connect a low-ESR capacitor from

this node to GND.

BLOCK DIAGRAM

+

–

0.4V

FAULT

FAULT

+

–

0.55V

+

–

0.49V

SS

ISS

3306 BD

VIN

VIN

SW

GND

FB OR

VOUT

PGOOD

L

COUT

VOUT

CIN

VIN

CSS

SWITCH LOGIC

AND

ANTI-SHOOT

THROUGH

Q

S

R

BURST

DETECT

+

–

OSCILLATOR

INTERNAL

REFERENCE

SLOPE

COMP

EN

R1

(OPT)

R2

(OPT)

0.55V

0.5V

0.49V

RC

CC

gm

0.5V

VC

C1

A1

B1

CMP

C2

B2

A2

RB

RA

NOTES:

1. FOR THE LTC3306 ADJUSTABLE VERSION, PIN C1 IS FB. FB IS HIGH IMPEDANCE AND RB

RESISTANCE IS INFINITE.

2. FOR THE LTC3306 FIXED OUTPUT VOLTAGE VERSIONS, PIN C1 IS VOUT. RB IS INTERNALLY SET

FOR THE REGULATION TARGET. VOUT PIN IS NOT HIGH IMPEDANCE AND WILL REGULATE TO

THE OUTPUT VOLTAGE TARGET.