5

FN9177.0

June 14, 2005

Functional Pin Descriptions

GND Pin

Bottom terminal pad of QFN package

Signal common of the IC. Unless otherwise stated, signals

are referenced to the GND pin, not the PGND pin.

VIN Pin-1 (Input)

The VIN pin measures the converter input voltage with

PWM modulator. The VIN pin is also the input source for the

integrated +5V LDO regulator.

VCC Pin-2 (Output)

The VCC pin is the output of the integrated +5V LDO

regulator, which provides the bias voltage for the IC. The

VCC pin delivers regulated +5V whenever the EN pin is

requires at least a 1µF MLCC decouple capacitor to the

GND pin.

FCCM Pin-3 (Logic)

The FCCM pin configures the controller to operate in forced-

continuous-conduction-mode (FCCM) or diode-emulation-

mode (DEM.) DEM is disabled when the FCCM pin is pulled

enabled when the FCCM pin is pulled below the falling

EN Pin-4 (Logic)

The EN pin is the on/off switch of the IC. When the EN pin is

ramp up and begin regulation. The soft-start sequence

COMP Pin-5 (Signal)

The COMP pin is the output of the control-loop error

amplifier. Loop compensation components connect from the

COMP pin to the FB pin.

FB Pin-6 (Signal)

The FB pin is the inverting input of the control loop error

amplifier. The converter will regulate to 600mV at the FB pin

with respect to the GND pin. Scale the desired output

voltage to 600mV with a voltage divider network made from

components connect from the FB pin to the COMP pin.

FSET Pin-7 (Signal)

The FSET pin programs the PWM switching frequency of the

VO Pin-8 (Input)

The VO pin makes a direct measurement of the converter

The VO pin should be connected to the top of feedback

Typical Application Schematic.

ISEN Pin-9 (Input)

The ISEN pin is the input to the overcurrent protection (OCP)

and short-circuit protection (SCP) circuits. Connect a resistor

reaches the desired OCP setpoint. The SCP threshold

PGND Pin-10

The PGND pin should be connected to the source of the low-

side MOSFET, preferably with an isolated path that is in

parallel with the trace connecting the LG pin to the gate of

the MOSFET. The PGND pin is an isolated path used

exclusively to conduct the turn-off transient current that flows

out the PGND pin, through the gate-source capacitance of

the low-side MOSFET, into the LG pin, and back to the

PGND pin through the pull-down resistance of the LG driver.

The adaptive shoot-through protection circuit, measures the

low-side MOSFET gate voltage with respect to the PGND

pin, not the GND pin.

LG Pin-11 (Output)

The LG pin is the output of the low-side MOSFET gate

driver. Connect to the gate of the low-side MOSFET.

PVCC Pin-12 (Input)

The PVCC pin is the input voltage for the low-side MOSFET

gate driver LG. Connect a +5V power source to the PVCC

pin with respect to the GND pin, a 1µF MLCC bypass

capacitor needs to be connected from the PVCC pin to the

PGND pin, not the GND pin. The VCC output may be used

for the PVCC input voltage source. Connect the VCC pin to

the PVCC pin through a low-pass filter consisting of a

resistor and the PVCC bypass capacitor. Refer to Figure 1,

Typical Application Schematic.

ISL6269