AN2738 datasheet(23/54 Pages) STMICROELECTRONICS

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AN2738

Application example

Doc ID 14589 Rev 2

23/54

8.1

VCC supply pin

Regarding the VCC pin, a local filtering of the supply voltage very close to the L6390 IC is

recommended. Generally the suggestion is to use two capacitors, one electrolytic with

greater value (CVCC1 = 10 µF, for example) which has a great energy capability but also a

not negligible ESR (so is quite slow in providing the current) and a second smaller ceramic

capacitor (CVCC2 = 100 nF) which has a lower ESR value but a lower energy capability. The

first capacitor works mainly as bulk energy storage while the second one is able to supply

the dynamic current spikes required by the commutations of the device, so is better for high

frequency decoupling of the IC supply voltage. On the other hand, the selection of the

proper value for the CBOOT capacitor is already described in Section 7.

Figure 20.

Ex. of an application circuit for one of the three half-bridges of a 3-phase

power stage

In the example a VCC supply voltage of 15 V is used. This voltage is approximately the

same voltage provided to the gate of the power switches.

8.2

BOOT (floating) supply pin

The bootstrap capacitor to supply the high-side floating section of the gate driver must be

placed between the BOOT pin 16 and the OUT pin 14. For a deep description of the proper

dimensioning of the bootstrap capacitor please refer to Section 7 on page 18. The capacitor

must be placed as close as possible to the related IC pins. The bootstrap diode required for

the charge of the bootstrap capacitor is integrated inside the L6390 device.

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