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LTC1553

5-Bit Programmable Synchronous Switching Regulator Controller for Pentium® II Processor

Linear Technology 

LTC1553

PIN FUNCTIONS

VID0, VID1, VID2, VID3, VID4 (Pins 18, 17, 16, 15, 14):

Digital Voltage Select. TTL inputs used to set the regulated

output voltage required by the processor (Table 3). There

is an internal 20kΩ pull-up at each pin. When all five VIDn

pins are high or floating, the chip will shut down.

OUTEN (Pin 19): Output Enable. TTL input which enables

the output voltage. The external MOSFET temperature can

be monitored with an external thermistor as shown in

Figure 13. When the OUTEN input voltage drops below 2V,

OT trips. As OUTEN drops below 1.7V, the drivers are

internally disabled to prevent the MOSFETs from heating

further. If OUTEN is less than 1.2V for longer than 30µs,

the LTC1553 will enter shutdown mode. The internal

oscillator can be synchronized to a faster external clock by

applying the external clocking signal to the OUTEN pin.

G1 (Pin 20): Gate Drive for the Upper N-Channel MOSFET,

Q1. This output will swing from PVCC to GND. It will always

be low when G2 is high or the output is disabled.

BLOCK DIAGRAM

115% VREF

OUTEN 19

COMP 10

SS 9

+

FC

–

12 FAULT

11 OT

LOGIC

DISDR

SYSTEM

POWER

DOWN

–

R

PWM

S

+

ISS

QSS

DELAY

13 PWRGD

2 PVCC

20 G1

1 G2

ERR

VREF

MHCL

HCL MONO

MIN

VREF – 5%

CC

MAX

FB

VREF + 5%

8 IFB

7 IMAX

IMAX

LVC

VREF

0.5VREF/

0.7VREF

BG

DAC

6 SENSE

18 VID0

17 VID1

16 VID2

15 VID3

14 VID4

1553 BD

7

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