US3033

4-3

Rev. 1.5

1/14/99

PIN DESCRIPTIONS

PIN DESCRIPTIONS

PIN #

PIN SYMBOL

PIN DESCRIPTION

BLOCK DIAGRAM

BLOCK DIAGRAM

Figure 1 - Simplified block diagram of the US3033

Vref

UVLO

1.25V

PWM Control

V12sw

Vhyst

Vfb2

Drv 1

Gnd

Vfb 1

Drv 2

5

1

2

4

3

6

7

3033blk1-1.0

V12

8

5V Reg

A resistor divider from this pin to the output of the switching regulator and ground sets the

Core supply voltage.

The feedback pin of the linear regulator. A resistor divider from this pin to the output of the

linear regulator and ground sets the I/O supply voltage.

The drive pin of the linear regulator. This pin controls the base of a transistor or the gate

of a MOSFET acting as the series pass element for the linear regulator.

This pin is connected to the IC substrate and must be connected to the lowest potential

in the system.

The PWM output of the switching controller. This pin is a totem pole drive that is con-

nected to the gate of the power MOSFET. A resistor may be placed from this pin to the

gate in order to reduce switching noise.

output ripple voltage for the switching regulator.

This pin supplies the voltage to the PWM drive and hysterises circuitry and it is con-

nected to the 12V supply. A 1 uF, high frequency capacitor must be connected from this

pin to ground to provide the peak current for charging and discharging of the MOSFET.

This pin provides the biasing for the chip and drive for the linear regulator controller. It

isconnected to 12V supply. A 10 ohm resistor in series from this pin to the 12V supply

and a 1uF, high frequency capacitor connected from this pin to Gnd is required to filter

the switching noise of the switching regulator.

3

6

7

Drv2

5

Gnd

1

Drv1

4

2

8