DRV8718-Q1: The GHx is uncontrolled, with an output of 10.7V.

? ?

Part Number: DRV8718-Q1

Tool/software:

Hello.
We use DRV8718SQRVJRQ1 when driving PSD motor (CH1 and CH2 channels) through PWM.
Remove R29 and R61 and turn the PSD motor (CH1 and CH2 channels), and the CH3(TP44) and CH4 (TP91) voltage is measured at 10.7V.
What could be the cause of this phenomenon?
We want CH3(TP44) and CH4 (TP91) to output low levels in this state.We set CH3 and CH4 to Hi-Z, but it doesn't work.
Best wishes.

5 months ago

0 Shinya Morita 5 months ago

TI__Mastermind 44405 points

Hi,

Thank you for your questions.

Please be aware that SHx and GHx are internally connected through R_PD_HS resister.

While commanding HiZ for channels, SH pin has weak pull up therefore, GH and SH could be ~PVDD. Please refer this link.

e2e.ti.com/.../drv8705s-q1evm-why-the-ghx-is-high-level-when-the-nsleep-is-high-level

regards

Shinya

0 ? ? 5 months ago in reply to Shinya Morita

Prodigy 30 points

Hello,
When the PSD motor (CH1 and CH2 channels) is driven by PWM, R29 and R61 are retained, then the PSD motor (CH1 and CH2 channels) is turned, and the voltage of both CH3(TP44) and TP38 is measured at 7V. What are the possible reasons for this phenomenon?
We want CH3(TP44) and CH4(TP91) to output low levels in this state. We set CH3 and CH4 to Hi-Z, but it didn't work.

Best wishes.

0 Shinya Morita 5 months ago in reply to ? ?

TI__Mastermind 44405 points

Hi,

Thank you for your questions. Will feedback to you within 24hours

0 Shinya Morita 5 months ago in reply to Shinya Morita

TI__Mastermind 44405 points

Hi,

Thank you for your questions.

I found one critical issue on your schematic. Please remove your 100Kohm resister from Gate to GND. R33/R43/R58/R68. R32,R42,R50,R67.

Please refer datasheet. DRV is not designed to have resister between gate to GND.

After you remove these resisters, you will see GH-SH=~0V during HiZ state. SH could be ~PVDD due to weak pull up. So SH=GH will be ~PVDD.

https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1246502/drv8705s-q1evm-why-the-ghx-is-high-level-when-the-nsleep-is-high-level?tisearch=e2e-sitesearch&keymatch=DRV8705S-Q1EVM

regards

Shinya

0 ? ? 5 months ago in reply to Shinya Morita

Prodigy 30 points

Hi

I have the following questions about the TI pre-driver having a weak pull-up path for the SH pin in the "Hiz" state.

◆Question 1

When the SH pin is pulled up, won't the PSD motor + terminal (=SH1) and the PSD motor - terminal (=SH2) have the same potential, creating a closed circuit?

◆Question 2

Is there a concern that when the SH5 pin is pulled up, current will flow through the release motor, causing it to rotate?

◆Question 3
By the way, how many ohms is it pulled up to PVDD with?

Thank you.

0 Shinya Morita 5 months ago in reply to ? ?

TI__Mastermind 44405 points

Hi,

Thank you for your questions. Let me review then and feedback to you in a day or two.

regards

Shinya

0 ? ? 5 months ago in reply to Shinya Morita

Prodigy 30 points

Hi Shinya,

Thank you for your feedback,
On question 1, I would like to add the following:

Due to the nature of the PSD system, a closed circuit will mean that the functional requirements cannot be met.

Since the PSD motor can be turned on and off manually, do you have any other suggestions if the demand cannot be met?

Best wishes
Jack

0 Shinya Morita 5 months ago in reply to ? ?

TI__Mastermind 44405 points

Hi,

Thank you for your questions.

First of all, weak pull up does not turn on external FET. with 1Kohm pull down(less than 10mA), output can be ~0V. It means this weak pull up can not spin the motor due to weak driving capability.

1) Based on above, I believe your motor will not be spinning. So far, I saw many customers accepted this situation, because their big motor (Drove by gate driver) does not spin by such a weak pull up.

However, if you cannot accept SH=High for some reason, adding ~1Kohm between SH to GND could be workaround.

2) my feedback is same as 1)

3) it is ~100uA capability.

regards

Shinya Morita

0 ? ? 5 months ago in reply to Shinya Morita

Prodigy 30 points

Hi Shinya,

Thank you for your answer.

I have two additional questions.

◆Quetion1-1

Regarding "◆Question 1" I would like to know if there is a risk of the motor braking because SH1 (PSD M+) and SH2 (PSD M-) are at the same voltage.

◆Quetion2-1

In the answer to “～100 μA" means that a current of 100 μA or less flows through the release motor?

Best wishes
Jack

0 Shinya Morita 5 months ago in reply to ? ?

TI__Mastermind 44405 points

Hi Jack.

Thank you for your questions. Normally high current motor is connected to gate driver (~10-20+A). If small motor (e.g 500mA), FET integrated driver will be used.

1)DRV is not turning on external FET. This is weak pull up ~100uA capability. I expect big Motor cannot be braked with such a low current capability.

2) If both motor terminal are high/PVDD, no current flow. 100uA is driving capability of weak path.

regards

Shinya

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DRV8718-Q1: The GHx is uncontrolled, with an output of 10.7V.