DRV8718-Q1: 0.5V on low side bridge when offline diagnostic

Frank QIN

Part Number: DRV8718-Q1

Tool/software:

Hi Team,

When we are driving a motor with H bridge, during the offline diagnostic, there is a 0.5V voltage at the low side bridge.

When offline diagnostic, X2-72 is the low side, X2-50 is te high side. We measured there is 0.5V at X2-72. I assume there might be some leakage current as mentioned in the datasheet:

While the nSLEEP is high when we measured. If we cut off the sample resistor between SN2 and SP2, the SN2 and SP2 shows ~2.5V voltage.

Please kindly advise if this 0.5V voltage is caused by leakage current and what is the leakage path? Will this 0.5V impact the CSA function?

Thank you.

Best,

Frank

8 days ago

0 Ibinu Alaudeen Nadeera 5 days ago

TI__Expert 6940 points

Hi Frank,

Thanks for the question. The device expert from my team will look into this and get back to you.

Thanks,

Ibinu

0 Shinya Morita 1 day ago in reply to Ibinu Alaudeen Nadeera

TI__Mastermind 36055 points

Hi Frank,

Thank you for your questions.

Let me start with this behavior background. For Gate driver, showing "High:up to PVDD" is normal behavior while both HS and LS FET are turned off.

While HiZ of SH, both HS and LS FETs are off surely. However DRV has small current leak path to SH, therefore SH goes up to ~PVDD. This is very weak pull up, cannot drive motor.

I guess your customer may observed this "weak pull up" voltage basically. Then its voltage was dropped by external leak. If their external load is less than 1Kohm (or less), voltage could be close to close to 0V. If it is range of ~5+Kohm, they may see some voltage remaining.

https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1220756/drv8714-q1-drv8714-q1/4609044?tisearch=e2e-sitesearch&keymatch=DRV8714%2520HiZ#4609044

regards

Shinya Morita

0 Frank QIN 1 day ago in reply to Shinya Morita

TI__Expert 7480 points

Hi Morita-san,

Thanks for your feedback. There might be some misunderstanding.

We have tried to cut off the SP2 and SN2 connection to sampling resistor, the same location as SN2[8] and SP2[8], then we found the voltage on SHx bridge turns to 0, and the voltage on SN and SP are still 2.5V. Which means the voltage or leakage current is from SP&SN, not the SHx.

Could you please clarify if there is voltage or current on SP&SN is correct during the offline diagnostic?

Thank you

Best,

Frank

0 Shinya Morita 12 hours ago in reply to Frank QIN

TI__Mastermind 36055 points

Hi Frank,

I understood your point. Thanks.

>>Please kindly advise if this 0.5V voltage is caused by leakage current and what is the leakage path? Will this 0.5V impact the CSA function?

This 0.5V could be leakage path from CSA. then this should not be issue for CSA performance, because CSA has differential input amplifier. CSA should care V_SPx - V_SNx.

regards

Shinya

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DRV8718-Q1: 0.5V on low side bridge when offline diagnostic