DRV8873-Q1: How to control multiple nOL lines from one MCU output?

Dmitry Marukh

Part Number: DRV8873-Q1

We have 6 drivers on one board controlled by MCU. Each driver has individual nSLEEP signal, but all DISABLE pins connected together and switched to the ground via nFET. I would like to control all nOL pins in the same way, i.e. enable or disable OLP and OLA on all the drivers simultaneously, while preserving an ability to control driver sleep individually.

Unlike DISABLE pins, the nOL is pulled up internally to nSLEEP. This means that High nSLEEP level on any driver can theoretically be passed through the nOL pull-ups to other drivers. Maybe 2x450k will not overcome 100k pull-down on another nSLEEP, but it may trigger nOL there.

I am thinking I can split one nFET drain via diodes to all nOL pins. Also the answer to my previous question suggested that I should never leave nOL N/C. So, maybe I should add somewhat stronger (100k) external pull-ups to corresponding nSLEEP pins after diodes?

8 months ago

0 Shinya Morita 8 months ago

TI__Mastermind 28295 points

Hi,

Thank you for your question. Our expert will feedback to you within 24hours.

regards

Shinya Morita

0 Keerthivasan Kumanan 8 months ago in reply to Shinya Morita

TI__Expert 8335 points

Hello Dmitry,

The setup you have should be fine, but I am going to double check with an automotive person on the team. I think adding the 100 k external pullup resistor is a good idea as it is a stronger pullup then the internal one. What application is this for?

Best,

Keerthi

0 Dmitry Marukh 8 months ago in reply to Keerthivasan Kumanan

Prodigy 100 points

This is for a power seating module for wheelchairs.

0 Keerthivasan Kumanan 8 months ago in reply to Dmitry Marukh

TI__Expert 8335 points

Hello Dmitry,

Are your nSLEEP pins connected to a microcontroller and if so what kind of logic are you providing (3.3 V or 5 V).

Best,

Keerthi

0 Dmitry Marukh 8 months ago in reply to Keerthivasan Kumanan

Prodigy 100 points

Yes, all nSLEEP are connected to STM32 outputs with 3.3V logic.

By the way, I did a little more circuit analysis and it seems when nFET is switched ON everything should be OK even without the diodes and pull-ups. In this state all nOL are pulled hard to the ground as expected. Their 450k pull-ups to nSLEEP become parallel to 100k pull-downs, so all nSLEEP will simply have 82k pull-downs. Their actual level will then depend on MCU outputs, also as expected.

However when nFET is OFF it can be removed from consideration. Without diodes and external pull-ups the common nOL line becomes floating and connected by 450k resistors to some combination of high and low nSLEEP inputs. Therefore nOL logic level can be anywhere between 0 and 3.3V. This is the situation I am trying to avoid.

0 Dmitry Marukh 8 months ago in reply to Keerthivasan Kumanan

Prodigy 100 points

I now realize that the idea of using OD FET to drive nOL was a mistake. Since the nOL pins are never pulled up to 5V VDD (unlike DISABLE) the OD is unnecessary. These pins can be driven directly by 3.3V logic, which would guarantee their state and furthermore will not affect the function of nSLEEP. This was a case of overthinking.

0 Keerthivasan Kumanan 7 months ago in reply to Dmitry Marukh

TI__Expert 8335 points

Hello Dmitry,

Can you elaborate on what you mean by nOL is never pulled up to 5V VDD. It is pulled up to nSLEEP, which would be 5 V when it is not in sleep mode.

Best,

Keerthi

0 Dmitry Marukh 7 months ago in reply to Keerthivasan Kumanan

Prodigy 100 points

According to datasheet (and confirmed on actual working devices) nSLEEP works fine with 3.3V MCU logic. So, when not in sleep it will pull nOL up to 3.3V via 450k resistor. This is fine by me, it means I can connect shared nOL line directly to another MCU pin.

I could not do that with DISABLE input because it is internally pulled to 5V, so I had to use OD FET there.

+1 Keerthivasan Kumanan 7 months ago in reply to Dmitry Marukh

TI__Expert 8335 points

Hello Dmitry,

I understand now. The VIH min for the device and it is 1.6 V, so I agree your current setup should be fine. I am closing this thread.

Best,

Keerthi

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DRV8873-Q1: How to control multiple nOL lines from one MCU output?