DRV2700: DRV2700 shuts down when input voltage is less than 4.7V

Hi, Daria,

Welcome to E2E and thank you for your interest in our products!

Could you share the DRV2700 schematic portion, please? This will be useful in order to have a better approach to this issue.

Thank you!

Best regards,
Luis Fernando Rodríguez S.

Dear Luis,

I am attaching the picture of the schematic. 

Best regards,

Daria

Hi, Daria,

Thank you for the schematic circuit you provided.

The schematic actually seems to be correct. I didn't find anything that should be modified. Some questions:

- Are you changing the VDD level dynamically? I mean, are you reducing the VDD level slowly and then it fails at 4.7V?

- Do you have this issue with multiple samples? Have you tested on more units?

- Do you have details about the VBST level with the voltage below 4.7V and above 4.7V?

- Could you add a 10uF capacitor at VDD in order to ensure that it is correctly regulated?

- Could you also see if the analog inputs have a common-mode level below 4.7V? Could you take a scope capture of the IN+/IN- pins with VDD < 4.7V and VDD > 4.7V?

Thank you.

Best regards,
Luis Fernando Rodríguez S.

Dear Luis,

1. I am changing VDD from PSU. So I go up and down slowly. I also tried to turn ON/OFF PSU so there is a spike in power. 

2. I've tested 4 boards and one prototype board - all have the same issues. With the same voltage level.

3. The boost level stays around 30 at all the voltages and drops when VDD reaches 2.5

4. This might be problematic as my PCB is pretty small.

5. Right now I connected the IN- to GND using resistor R1. So this level is always 0.

I am attaching some images of OUT+ voltage levels depending on different VDDs. (I made a mistake in the previous message, the voltage level is 5.0)

Best regards,

Daria

Hi, Daria,

Thank you for your response.

The boost level (30V) is correct based on the resistors that you selected. This means that the boost is working as expected. So, the problem could be associated to the amplifier side.

We had a similar issue before where the boost worked, but the amplifier did not:

https://e2e.ti.com/support/motor-drivers/f/38/p/943853/3492829#3492829

It seems that the PVDD capacitor needs to be close to the device in order to ensure a proper VBST level at this pin.

In addition, regarding the input level measurement, I actually referred to the level at the input pins. Even if you connect the input capacitors to GND, the pins should show a common-mode level.

Best regards,
Luis Fernando Rodríguez S.

Hi, Daria,

Excuse me, do you have a feedback on this? Were you able to take a look at my recommendations above?

Thank you.

Best regards,
Luis Fernando Rodríguez S.

Dear Luis,

Im going to conduct more tests tonight and I will update you on the results. Thank you!

Best regards,

Daria

I experimented a little with the capacitor. And as I have the PCB done already, I did pretty ugly patches. So once I used patches, the VDD on which the buzzer was working, was moving either right or left on 0.1 / 0.2 V. 

I think my layout is far not optimal so this might be an issue. Although can the capacitor influence the functionality so much? I actually also noticed that after 5.4 the buzzer returns to the same state as before 5.0)

Best regards,

Daria

Hi, Daria,

Thank you for your feedback.

Especially for the Vbst level, the capacitor is crucial for a good behavior. Since the device handles a high voltage level, the Vbst output may have a high ripple content. The capacitor helps to mitigate the ripple and have a proper PVDD level.

Best regards,
Luis Fernando Rodríguez S.