Is L7987 Synchronous or Asynchronous?

[AziD32]

Hi all,

I am designing a 48 volt to 12 volt 3 amp DCDC asynchronous buck converter (with frequency > 200kHz) and I found the L7987. Although it says asynchronous in the datasheet, it looks like synchronous in the block diagram. I am confused, can someone explain?

[Peter BENSCH]

Welcome @AziD32, to the community!

The low-side MOSFET that you see in the block diagram is not the MOSFET known for synchronous switching regulators, but serves a different purpose. The data sheet describes this in section 4.3:

In order to let the bootstrap capacitor recharge, in case of extremely light load the L7987 is able to pull-down the LX net (pin OUT) through an integrated small LS MOS. In this way the bootstrap recharge current can flow from VIN through CBOOT, LX and the LS MOS.

The L7987 is therefore actually a classic asynchronous buck.

I hope, that answers your question?

Regards
/Peter

[AziD32]

Actually no, i already know that thank you for your explanation but the following link helped a little. Maybe you wanna take a look

https://electronicspost.com/why-is-there-a-bootstrap-capacitor-in-all-dcdc-chip-designs/ 

 

[Peter BENSCH]

The website of your link is generally limited to the reason for a boost capacitor.

Your question, on the other hand, was aimed at the integrated low-side, from which you wanted to deduce synchronous operation - which is not correct.