LT8551 datasheet(14/32 Pages) AD

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LT8551

Rev 0

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OPERATION

and the slaves (in Figure 1). Under normal operation, the

CLK2 frequency is at the CLK1 frequency times the total

distinct phase number (TDPN), as shown in Figure 2. The

number shown above the CLK2 pulses in Figure 2 is called

the phase angle number (PAN).

Figure 1.

REG

• • •

8551 F01

MASTER

LT8551

SYNC

CLK1

CLK2

RT/MS

PRIMARY

CONTROLLER

SYNC

SLAVE

LT8551

SYNC

CLK1

CLK2

RT/MS

SLAVE

LT8551

SYNC

CLK1

CLK2

RT/MS

Clock Configuration in a Multiple LT8551 System

The total distinct phase number is programmed through

the master LT8551’s PHS1, PHS2 and PHS3 pins, accord-

ing to Table 1. There is a delay locked loop in the chip

which can force the primary controller’s BG (Bottom Gate)

rising edge to align with the pulse whose phase angle

number equals the TDPN (in Figure 2).

Each expanded channel chooses one pulse from CLK2 in

one CLK1 clock cycle. The rising edge of this chosen pulse

aligns with the corresponding channel’s bottom gate turn

on edge with a very short delay. The master LT8551’s

channel 1 to channel 4 always choose the pulses whose

phase angle number equals 1 to 4, respectively. Four chan-

nels of a slave LT8551 choose pulses with four consecu-

tive phase angles. The phase angle number of the slave

LT8551’s channel 1 pulse is also programmed through

PHS1, PHS2 and PHS3 pins, according to Table 1, and

the pulses of the slave LT8551’s channel 2, channel 3

and channel 4 have the next three phase angle number in

succession. LT8551.

Table 2 shows the PHS1, PHS2 and PHS3 connections

for a two LT8551 system with a total of 9 phases, includ-

ing the primary controller’s phase, as an example. The

primary controller uses the CLK1 signal. The clocks used

by the eight expanded channels are shown in Figure 3.

When the primary controller skips one or more pulses,

the expanded channels also skip the same number of

pulse(s). This function is realized by CLK2. As shown in

Figure 4, when the primary controller skips one BG pulse,

the CLK2 also skips a group of pulses with phase number

from 1 to TDPN.

Table 1. Table for Programming Total Distinct Phase Number

(TDPN) and Phase Angle Number (PAN)

PHS3

PHS2

PHS1

TDPN For

Master

PAN of Slave

Channel 1 Pulse

GND

REG

GND

Floating

GND

REG

GND

REG

GND

REG

Floating

GND

Floating

GND

Floating

REG

GND

Floating

REG

GND

REG

GND

REG

GND

Floating

REG

GND

REG

Floating

REG

Floating

GND

REG

Floating

REG

Floating

Table 2. Design Example for a 9-Phase Application

PHS3

PHS2

PHS1

PAN for Channel 1,

2, 3 and 4

Master LT8551

GND

Floating

1, 2, 3, 4

Slave LT8551

GND

REG

5, 6, 7, 8

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