US3034

4-3

Rev. 1.8

1/13/99

PIN DESCRIPTIONS

PIN DESCRIPTIONS

PIN #

PIN SYMBOL

PIN DESCRIPTION

BLOCK DIAGRAM

BLOCK DIAGRAM

Figure 1 - Simplified block diagram of the US3034

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

Core supply voltage.

This pin is connected to the minus side of the external current sense resistor. An internal

current source together with an external resistor in series with this pin programs the

current limit threshold voltage. This voltage divided by the external current sense resistor

sets the current limit threshold.

This pin is connected to the plus side of the external current sense resistor. A resistor in

series with this pin and a capacitor connected between this pin and pin 6 provides a high

frequency filtering for the noise spikes of turn on and turn off switching.

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 soft start for the regulator during power up. It also sets a long off

time when the converter goes into current limiting, providing low duty cycle for the catch

diode allowing it to survive during short circuit.

3

6

C.S-

7

C.S+

5

Gnd

1

Drv

4

2

8

S.S

Vref

UVLO

1.25V

PWM Control

V12

Vhyst

CS+

Drv

Gnd

Vfb

CS-

5

1

2

4

3

7

6

3034blk1-1.1

SS

8

5V Reg

S.S. / Hiccup

Control

20uA

R

3R