SYNC

10k

S

R

Q

Q

DEADTIME

ONE-SHOT

5V

2.5V

I = f(RT)

SYNC

LM25574

UP TO 5 TOTAL

DEVICES

LM25574

SYNC

SYNC

AGND

LM25574

SW

CLK

SYNC

SW

500 ns

LM25574, LM25574-Q1

SNVS483G – JANUARY 2007 – REVISED APRIL 2013

www.ti.com

Figure 10. Sync from External Clock

Figure 11. Sync from Multiple Devices

Multiple LM25574 devices can be synchronized together simply by connecting the SYNC pins together. In this

configuration all of the devices will be synchronized to the highest frequency device. The diagram in Figure 12

illustrates the SYNC input/output features of the LM25574. The internal oscillator circuit drives the SYNC pin with

a strong pull-down / weak pull-up inverter. When the SYNC pin is pulled low either by the internal oscillator or an

external clock, the ramp cycle of the oscillator is terminated and a new oscillator cycle begins. Thus, if the SYNC

pins of several LM25574 IC’s are connected together, the IC with the highest internal clock frequency will pull the

connected SYNC pins low first and terminate the oscillator ramp cycles of the other IC’s. The LM25574 with the

highest programmed clock frequency will serve as the master and control the switching frequency of the all the

devices with lower oscillator frequency.

Figure 12. Simplified Oscillator Block Diagram and SYNC I/O Circuit

10

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