I make a board with a L6235PD driver. On a population of 5 controllers, 3 have a problem.... Means that when the Vref is @0V, the motor still running (at low speed, but still running).

FSamu.2 · ‎2022-11-29

I've certainly a problem with the RC OFF and RC Pulse definition....

On RC pulse: 82k / 22nF

On RC OFF: 91k/470pF

Do you have an idea to solve my problem??? Thanks for your help.

Cristiana SCARAMEL · ‎2022-11-30

Hello @FSamu.2 and welcome to the ST Community.

For a better support could you share your custom schematic?

In the meantime, I’m going to give you some information that I hope will be useful.

The PWM comparator has an input offset voltage that can be both positive or negative.

If the input offset is positive, the comparator output can be high although the Vref pin is @ 0V or directly connected to ground.

As a consequence the power bridges are turned on for a period equal to the minimum on-time (see application note AN1625, page 15), that is probably enough to bring the sense voltage over the comparator offset voltage. After that the output are turned off for the programmed off-time.

In order to force the device to not drive the motor, you can set low the BRAKE (all the high-side MOS switch on, brake function) or EN pin (all MOS switch off).

Concerning the timing definition with your RC components:

OFF time is about 27 us
PULSE time is about 1 ms

You can refer to the AN1625 for more details on the timing setting.

Let me know if these info are useful to you.

FSamu.2 · ‎2022-11-30

Hi Christiana, Thanks for this answer.

We would like to not use the pin brake so as not to run the motor and have a motor that does not run with Vref at 0. Do you think that if we modify the Toff (big enough compared to the min on time) the motor will not run?

Do you have another idea to compensate for this offset?

Here is my schematic:

Cristiana SCARAMEL · ‎2022-11-30

Hi @FSamu.2,

the device is designed to impose a phases current except when it is in brake (BRAKE low) or when disabled (EN low).

Making the current very small by stretching the Off Time would seem to be the best strategy, but on the other hand you would have very large ripple during normal operation.

This important drawback, makes the strategy not applicable.