L6730C datasheet(26/50 Pages) STMICROELECTRONICS

26 / 50 page

Device description

L6730C - L6730D

26/50

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 21. 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) L6730, 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

(fEXT) to synchronize one or more devices that are working at a different switching frequency

(fSW) it is recommended to follow the below formula:

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

Table 6.

S/O/U pin; CC/O/U pin

VSOU/VCCDR

UVLO

OVP

SINK CC

N.C

Ω

5V BUS

Not Latched

Not

11K

Ω

2.7K

Ω

0.2

5V BUS

Not Latched

Yes

6.2K

Ω

2.7K

Ω

0.3

5V BUS

Latched

Not

4.3K

Ω

2.7K

Ω

0.4

5V BUS

Latched

Yes

2.7K

Ω

2.7K

Ω

0.5

12V BUS

Not Latched

Not

1.8K

Ω

2.7K

Ω

0.6

12V BUS

Not Latched

Yes

1.2K

Ω

2.7K

Ω

0.7

12V BUS

Latched

Not

Ω

N.C

12V BUS

Latched

Yes

Figure 21. Synchronization.

PWM SIGNALS

INDUCTOR CURRENTS

EXT

⋅

≤

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