4-4

Rev. 1.0

5/6/98

US3012/3012A

PIN DESCRIPTIONS

PIN DESCRIPTIONS

Pin Description

LSB input to the DAC that programs the output voltage. This pin can be pulled up exter-

nally by a 10k resistor to either 3.3V or 5V supply.

Input to the DAC that programs the output voltage.This pin can be pulled up externally by

a 10k

Ω resistor to either 3.3V or 5V supply.

Input to the DAC that programs the output voltage.This pin can be pulled up externally by

a 10k resistor to either 3.3V or 5V supply.

MSB input to the DAC that programs the output voltage.This pin can be pulled up exter-

nally by a 10k resistor to either 3.3V or 5V supply.

This pin selects a range of output voltages for the DAC. The voltage range for both the "A"

and the none "A" versions of the device is given in table 1.

This pin is an open collector output that switches LO when the output of the converter is

not within

±10% (typ) of the nominal output voltage.When PWRGD pin switches LO the

sat voltage is less than 0.4V at 3mA.

This pin is connected directly to the output of the Core supply to provide feedback to the

Error comparator.

This pin is connected to the Drain of the power MOSFET of the Core supply and it

provides the positive sensing for the internal current sensing circuitry. An external resis-

tor programs the C.S threshold depending on the Rds of the power MOSFET. An external

capacitor is placed in parallel with the programming resistor to provide high frequency

noise filtering.

This pin is connected to the Source of the power MOSFET for the Core supply and it

provides the negative sensing for the internal current sensing circuitry.

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

charges an external capacitor that is conected from this pin to the GND which ramps up

the outputs of the switching regulator, preventing the outputs from overshooting as wellas

limiting the input current. The second function of the Soft Start cap is to provide long off

time for the synchronous MOSFET or the Catch diode (HICCUP) during current limiting.

This pin programs the oscillator frequency in the range of 50 kHZ to 500kHZ with an

external capacitor connected from this pin to the GND.

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

high frequency capacitor (0.1 to 1 uF) must be connected from V5 and V12 pins to this

pin for noise free operation.

Output driver for the synchronous power MOSFET.

Output driver for the high side power MOSFET.

This pin is connected to the 12 V supply and serves as the power Vcc pin for the output

drivers.A high frequency capacitor (0.1 to 1 uF) must be connected directly from this pin

to GND pin in order to supply the peak current to the power MOSFET during the transi-

tions.

5V supply voltage.

This is the output enable pin.This pin is internally pulled high through a resistor to 5V

supply. A low signal on this pin disables the output.

No connect.

PIN# PIN SYMBOL

20

D0

19

D1

18

D2

17

D3

8

D4

3

PGd

14

Vfb

4

CS+

5

CS-

16

SS

1

Ct

10

Gnd

9

LDrv

12

HDrv

13

V12

6

V5

2

OUTEN

7,11

N.C

15