SC1157

PROGRAMMABLE SYNCHRONOUS DC/DC

CONTROLLER FOR ADVANCED PROCESSORS

© 2000 SEMTECH CORP.

652 MITCHELL ROAD NEWBURY PARK CA 91320

Preliminary - August 7, 2000

4

NOTE:

(1) All VID codes not specifically listed are invalid and cause shutdown exactly as if the shutdown pin had been

asserted.

THEORY OF OPERATION

The voltage at the VOSENSE pin is applied, through the internal precision resistor feedback chain, to the inverting

input of the error amplifier. The non-inverting input of the error amplifier is supplied with a DC voltage derived by

the DAC from the internal trimmed bandgap voltage reference. The output of the error amplifier is compared to the

triangular output of the internal oscillator to generate a fixed frequency, variable duty cycle pulse train. The internal

oscillator uses an on-chip capacitor and precision trimmed current sources to set the frequency to 100 kHz.

The generated pulse train is gated with the output of the current limit latch and the inhibit signal to produce a drive

signal for the upper FET. It is also inverted to produce a drive signal for the lower FET. These FET drive signals

are modified by the “shoot-through control” circuitry so that the top FET turn-on is delayed until the bottom FET has

turned off, and visa-versa.

The current limit latch is set (ending the upper FET drive pulse early) if the current limit comparator indicates an

overcurrent condition. The latch is reset at the start of each oscillator period.

OUTPUT VOLTAGE TABLE

Unless specified: V

T

PARAMETER

CONDITIONS

VID

3210

MIN

TYP

MAX

UNITS

Output Voltage

(1)

I

1111

1.287

1.300

1.313

V

(Figure 1)

1110

1.337

1.350

1.364

1101

1.386

1.400

1.414

1100

1.436

1.450

1.465

1011

1.485

1.500

1.515

1010

1.535

1.550

1.566

1001

1.584

1.600

1.616

1000

1.634

1.650

1.667

0111

1.683

1.700

1.717

0110

1.733

1.750

1.768

0101

1.782

1.800

1.818

0100

1.832

1.850

1.869

0011

1.881

1.900

1.919

0010

1.931

1.950

1.970

0001

1.980

2.000

2.020

0000

2.030

2.050

2.070