SC1156SW.TR(2001) 데이터 시트보기 (PDF) - Semtech Corporation

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SC1156SW.TR
(Rev.:2001)

Programmable Synchronous DC/DC Controller for Advanced Microprocessors

Semtech Corporation 

SC1156

POWER MANAGEMENT

Block Diagram

VID4

VID3

VID2

VID1

VID0

VOSENSE

1.25V REF

D/A

PWRGOOD

OVP

OPEN

COLLECTORS

+

-

+

-

VCC

+

-

VCC CS- CS+

SHUTDOWN

70mV

CURRENT LIMIT

+

-

OSCILLATOR

R

Q

S

-

+

+

-

ERROR

AMP

GND

EN

LEVEL SHIFT

AND DRIVE

BSTH

DH

PGNDH

SHOOT-THRU

CONTROL

LOW SIDE

DRIVE

BSTDL

DL

PGNDL

Theory of Operation

The D/A Converter generates an output voltage determined

by an internal trimmed bandgap voltage reference and

the status of the VID0 through VID4 inputs. This voltage is

applied to the non-inverting input of the error amplifier,

the inverting input of the error amplifier is fed from the

VOSENSE pin via a precision resistor divider. The error

amplifier itself is a transconductance amplifier with an in-

ternal load resistor. The open loop gain is internally set to

approximately 40 dB.

The internal oscillator uses an on-chip capacitor and a

trimmed precision current source to set the frequency of

oscillation to 200 kHz. The triangular output of the oscil-

lator is compared to the output of the error amplifier. The

output of the PWM comparator is a pulse width modu-

lated signal whose duty cycle increases as the voltage at

the VOSENSE pin decreases.

The output of the current limit comparator goes high when

its input voltage exceeds approximately 70mV, this sets

the current limit latch, immediately terminating the cur-

rent ON time. The current limit latch is reset in the middle

of the OFF time when the triangular wave oscillator reaches

its highest point .

When the output of the PWM comparator is high, output

DH is driven high, provided that the VID code is valid, the

current limit latch has not been set and the Enable (EN)

pin is not pulled low. When the PWM comparator output is

low DL is always driven high.

The Shoot-through control circuitry modifies the DH and

DL waveforms slightly, ensuring that there is a short delay

between one turning OFF and the other turning ON. This

ensures that the ON times of the external FETs driven by

DH and DL do not overlap.

© 2000 Semtech Corp.

4

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