Device description

L6725 - L6725A

16/32

5.11

Synchronization

The presence of many converters on the same board can generate beating frequency noise. To

avoid this it is important to make them operate at the same switching frequency. Moreover, a

phase shift between different modules helps to minimize the RMS current on the common input

capacitors. Figure 10. and Figure 11. shows the results of two modules in synchronization. Two

or more devices can be synchronized simply connecting together the SYNCH pins. The device

with the higher switching frequency will be the Master while the other one will be the Slave. The

Slave controller will increase its switching frequency reducing the ramp amplitude proportionally

and then the modulator gain will be increased.

To avoid a huge variation of the modulator gain, the best way to synchronize two or more

devices is to make them work at the same switching frequency and, in any case, the switching

frequencies can differ for a maximum of 50% of the lowest one. If, during synchronization

between two (or more) L6725A, it's important to know in advance which the master is, it's timely

to set its switching frequency at least 15% higher than the slave. Using an external clock signal

The phase shift between master and slaves is approximately 180°.

Figure 10. Synchronization: PWM Signal

Figure 11. Synchronization: Inductor Currents

SW

EXT

SW

f

f

f

⋅

≤

≤

3

,

1