L6725_07 STMICROELECTRONICS [STMicroelectronics], L6725_07 Datasheet - Page 16

• Manufacturer Part Number: L6725_07
• Description: Voltage mode PWM controller with bootstrap anti-discharging system
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Device description
5.11
Figure 10. Synchronization: PWM Signal
Figure 11. Synchronization: Inductor Currents
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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.
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
(f
(f
The phase shift between master and slaves is approximately 180°.
EXT
SW
) it is recommended to follow the below formula:
) to synchronize one or more devices that are working at a different switching frequency
Figure 10.
and
Figure 11.
f
SW
≤
shows the results of two modules in synchronization. Two
f
EXT
≤
1
3 ,
⋅
f
SW
L6725 - L6725A