IRU3038

3

Rev. 2.0

09/12/02

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.

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 to 1

mF) must be connected from

Vcc and Vc pins to this pin for noise free operation.

Output driver for the high side power MOSFET. Connect a diode, such as BAT54 or 1N4148,

from this pin to ground for the application 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.

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 0.5V.

Error Amp

Fb Voltage Input Bias Current

Fb Voltage Input Bias Current

Transconductance

Oscillator

Frequency

Ramp Amplitude

Output Drivers

Rise Time

Fall Time

Dead Band Time

Max Duty Cycle

Min Duty Cycle

SS=3V, Fb=1V

SS=0V, Fb=1V

Rt=Open

Rt=Gnd

Fb=1V, Freq=200KHz

Fb=1.5V

0.8

450

180

360

1.225

50

85

0

-0.1

-64

600

200

400

1.25

50

50

150

90

0

mA

mA

V

mmho

KHz

V

ns

ns

ns

%

%

PIN#

PIN SYMBOL

PIN DESCRIPTION

1

2

3

4

5

14

6

7

8

9

10

11

12

13

Fb

Vcc

NC

LDrv

Gnd

PGnd

HDrv

Vc

Rt

Comp

SS

Freq

1.5

750

220

440

1.275

100

100

250

95