L6730 datasheet(28/52 Pages) STMICROELECTRONICS

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Device description

L6730 - L6730B

28/52

Doc ID 11938 Rev 3

Table 7 shows how to set the different options through an external resistor divider:

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 24 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:

Figure 23.

External resistor

Table 7.

S/O/U and CC/O/U pin

VSOU/VCCDR

UVLO

OVP

SINK CC

N.C

5V BUS

Not latched

Not

11K

2.7K

0.2

5V BUS

Not latched

Yes

6.2K

2.7K

0.3

5V BUS

Latched

Not

4.3K

2.7K

0.4

5V BUS

Latched

Yes

2.7K

0.5

12V BUS

Not latched

Not

1.8K

2.7K

0.6

12V BUS

Not latched

Yes

1.2K

2.7K

0.7

12V BUS

Latched

Not

N.C

12V BUS

Latched

Yes

L6730/B

S/O/U

CC/O/U

VCCDR

EXT

⋅

≤

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