Datasheet

SYNC
10k
S
R
Q
Q
DEADTIME
ONE-SHOT
5V
2.5V
I = f(RT)
SYNC
LM5574
UP TO 5 TOTAL
DEVICES
LM5574
SYNC
SYNC
AGND
LM5574
SW
CLK
SYNC
SW
500 ns
LM5574, LM5574-Q1
SNVS478F –JANUARY 2007–REVISED APRIL 2013 www.ti.com
Figure 11. Sync from External Clock
Figure 12. Sync from Multiple Devices
Multiple LM5574 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 13
illustrates the SYNC input/output features of the LM5574. 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 LM5574 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 LM5574 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 13. Simplified Oscillator Block Diagram and SYNC I/O Circuit
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