IRU3138

3

Rev. 1.0

01/29/04

www.irf.com

PARAMETER

SYM

TEST CONDITION

MIN

TYP

MAX

UNITS

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

provide feedback to the Error amplifier.

Non-inverting input of error amplifier.

Reference Voltage.

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

driver. A minimum of 1

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

ground to provide peak drive current capability.

No Connection.

Output driver for the synchronous power MOSFET.

Analog ground for internal reference and control circuitry. Connect to PGnd with a short

trace.

This pin serves as the separate ground for MOSFET's drivers and should be connected to

system's ground plane. A high frequency capacitor (0.1

mF to 1mF) must be connected

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

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

provide peak drive current capability.

The switching frequency can be Programmed between 200KHz and 400KHz by connect-

ing a resistor between Rt and Gnd. Floating the pin set the switching frequency to 200KHz

and grounding the pin set the switching frequency to 400KHz.

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

Output Drivers

Rise Time

Fall Time

Dead Band Time

Max Duty Cycle

Min Duty Cycle

SS=3V, Fb=1V

SS=0V, Fb=1V

Fb=0.7V, Freq=200KHz

Fb=1.5V

0.7

500

85

0.1

50

800

35

35

100

90

mA

mA

V

mmho

ns

ns

ns

%

%

1

2

3

4

5

14

6

7

8

9

10

11

12

13

Fb

NC

LDrv

Gnd

PGnd

HDrv

Rt

Comp

SS / SD

GM

Tr

Ton

Toff

1.5

1000

70

70

0

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

PIN DESCRIPTIONS

PIN#

PIN SYMBOL

PIN DESCRIPTION