L6387 MOSFET driver on B-G431B-ESC1 Discovery kit: no 3.3V compliant inputs?

DUffm.1 · ‎2020-09-26

While finishing my porting of the B-G431B-ESC1 board for Arduino using STM32duino (which worked great - thanks STM team) I had to dive quite deep into the schematics. One thing that is unclear to me is if the L6387 MOSFET driver chips should be really used in this discovery board?

The L6387 Datasheet says its input are "CMOS/TTL compatible" which means (for TTL) a logic input > 2.4V should be considered as High Logic Input but the data table says:

It seems that L6387 requires > 3.6V on its logical inputs to safely turn on the respective output but STM32G431 is a 3.3V device and there are no level shifters used between MCU and MOSFET Driver.

Can you help me to understand if this will not cause any strange behavior during operation?

L6388E would seem to be a better choice as it has 3.3V CMOS compliant logical inputs.

DPetr.0 · ‎2021-07-06

I know this is an old thread, but, I'd also like to hear a reply to this question from ST. I am also using B-G431B-ESC1 eval board and have been developing my own firmware for it in order to drive two of the half bridges in an H-bridge mode for a DC motor in some applications. I'm seeing that whenever the logic inputs on the L6387 are driven in such a way that the high side is 100% on, the corresponding gate drive will not go high. If the logic input is at 99% duty cycle with 150ns of off time or more, then the device behaves as expected, but any time that input is driven high at 100% duty cycle the device no longer can drive the FET properly. In all other cases it works as expected. This might not be an issue for the application since 3 phase motor drivers would never operate in a DC condition like that, but it's just weird.

Peter BENSCH · ‎2021-07-12

Welcome, @DPetr.0, to the community!

The driver used on the B-G431B-ESC1 uses bootstrap technology to control the hi-side MOSFET and can therefore not be used for 100% duty cycle. Further details can be found in section 6 of the data sheet.

Regards

/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

Peter BENSCH · ‎2021-07-12

Even if this is indeed an old thread, I just want to confirm that the L6387E is CMOS compatible. The data sheet will be updated on this point soon.

Regards

/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.