IRU3137

3

Rev. 1.0

06/22/04

www.irf.com

PARAMETER

SYM

TEST CONDITION

MIN

TYP

MAX

UNITS

PIN DESCRIPTIONS

This pin is connected directly to the output of the switching regulator via resistor divider to

provide feedback to the Error amplifier.

This pin provides biasing for the internal blocks of the IC as well as power for the low side

driver. A minimum of 1

µF, high frequency capacitor must be connected from this pin to

ground to provide peak drive current capability.

Output driver for the synchronous power MOSFET.

This pin serves as the ground pin and must be connected directly to the ground plane. A

high frequency capacitor (0.1 to 1

µF) must be connected from VCC and Vc pins to this

pin for noise free operation.

Output driver for the high side power MOSFET. This pin should not go negative (below

ground), this may cause problem for the gate drive circuit. It can happen when the inductor

current goes negative (Source/Sink), soft-start at no load and for the fast load transient

from full load to no load. To prevent negative voltage at gate drive, a low forward voltage

drop diode might be connected between this pin and ground.

This pin is connected to a voltage that must be at least 4V higher than the bus voltage of

the switcher (assuming 5V threshold MOSFET) and powers the high side output driver. A

minimum of 1

µF, high frequency capacitor must be connected from this pin to ground to

provide peak drive current capability.

Compensation pin of the error amplifier. An external resistor and capacitor network is

typically connected from this pin to ground to provide loop compensation.

This pin provides soft-start for the switching regulator. An internal current source charges

an external capacitor that is connected from this pin to ground which ramps up the output

of the switching regulator, preventing it from overshooting as well as limiting the input

current. The converter can be shutdown by pulling this pin below 2.8V.

Error Amp

Fb Voltage Input Bias Current

Fb Voltage Input Bias Current

Transconductance

Oscillator

Frequency

Ramp-Amplitude Voltage

Output Drivers

Rise Time

Fall Time

Dead Band Time

Max Duty Cycle

Min Duty Cycle

SS=3V, Fb=1V

SS=0V, Fb=1V

Note 1

Fb=0.7V, Freq=200KHz

Fb=1.5V

600

180

85

0.1

50

850

1.25

35

35

100

90

µA

µA

µmho

KHz

V

ns

ns

ns

%

%

PIN#

PIN SYMBOL

PIN DESCRIPTION

1

2

3

4

5

6

7

8

Fb

Vcc

LDrv

Gnd

HDrv

Vc

Comp

SS / SD

GM

Freq

Tr

1100

240

70

70

0

Note 1: Guaranteed by design but not tested in production.