L6398 (IHM08M1) Input Logic Confusion: HIN/LIN Control Signals

[Esakkimuthu]

Hi all!

I am using the IHM08M1 power board for a BLDC/PMSM motor application, and I have a doubt regarding the L6398 gate driver input logic.

My question is:
If I use PWM to control the high-side MOSFET and a GPIO to control the low-side MOSFET, is this approach correct when working with the L6398 gate driver?

I am asking because I am currently using complementary PWM mode on my microcontroller. In complementary mode, the signals are inverted (PWM and its opposite), so HIN and LIN cannot receive the same logic level. Because of this, the L6398 truth table does not match, since the driver expects:

• HIN = HIGH, LIN = HIGH → High-side ON

• HIN = LOW, LIN = LOW → Low-side ON

With complementary PWM, this is impossible because the two signals are always opposite.
So I am considering using:

• PWM → HIN (high-side)

• GPIO → LIN (low-side)

I would like to know whether this method is valid, or if there is a better recommended way to drive the L6398 when only complementary PWM outputs are available.
Please let me know if my understanding is correct or if I am missing anything.

Thanks!

[Peter BENSCH]

The output polarity of the PWM outputs in the STM32 is freely selectable, so there is no problem there, but you obviously have a different MCU.

What's stopping you from outputting LIN inverted, since LIN is controlled by a GPIO in your case?

Otherwise, you can either invert LIN with an inverter or replace the L6398 with a L6399.

Hope that helps?

Regards
/Peter

[Esakkimuthu]

Yes, you’re right — on STM32 the PWM polarity can be freely inverted, but on my MCU the complementary outputs are fixed-polarity and I only get complementary channels for the low-side switches.

LIN is currently tied to a dedicated complementary PWM output, so I can’t directly invert it in hardware. I also don’t have an extra timer channel available to generate LIN as a separate, invertible PWM.

Using an external inverter on LIN or switching to an L6399 (which supports separate input pins for better flexibility) would indeed solve the problem, so I’ll consider those options.

Thanks for the clarification — it helps a lot.