DRV8702-Q1: SLEEP MODE

JILL LU

Part Number: DRV8702-Q1
Other Parts Discussed in Thread: DRV8872, DRV8705-Q1

We have a project that uses DRV8702-Q1 for motor and solenoid drive. We find that when nSleep = 0, SH1 or SH2 are always 0V regardless what mode the chip is running in (MODE =0, 1 or open). This is measured without load (OUTx open except the FET bridge), or with a pull up to an external voltage. I noticed there was a discussion on DRV8872 sleep mode state (https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/559509/drv8872-q1-in-sleep-state), and DRV8702-Q1 doesn't even get to sleep mode with OUTx is below 5V.

My questions are:

1) Is this a known behavior or have we done anything wrong to cause this behavior? I mean no Hi-Z at all.

2) Is there a similar chip that has a true Hi-Z state for H-bridge control? We choose DRV8702-Q1 because of its wide operating supply voltage (up to 45V).

over 3 years ago

0 Ryan Kehr over 3 years ago

TI__Guru 55605 points

Jill,

The FETs themselves should be in HIZ state. Meaning, both low-side and high-side external FET are OFF.

If you add a pull-up resistor on SHx pins as a test (10k), you will see that the voltage will rise on SHx pins. This is due to a leakage path into SHx pins when in nSLEEP state.

Regards,

Ryan

0 JILL LU over 3 years ago in reply to Ryan Kehr

Prodigy 10 points

We did that. We had a 16K resister pulling up to from 3V to 12V (supply is 12V) and the voltage on SHx at maximum is about 1V

0 Ryan Kehr over 3 years ago in reply to JILL LU

TI__Guru 55605 points

Jill,

It sounds like the part is behaving as expected then.

It is normal for the voltage on SHx pins to be ~1V in sleep mode if pulled up with external source. In sleep mode, the high side FETs are turned off and the FET's gate are pulled down which generates a leakage path from SHx to ground through the FET's gate to source clamp circuit.

The table in the datasheet showing "HIZ" for the SHx pins is misleading. The FETs are in the HIZ state, but because of this internal VGS clamp, the voltage will be clamped to ~1V as you measured.

Regards,

Ryan

0 JILL LU over 3 years ago in reply to Ryan Kehr

Prodigy 10 points

Thank you. Does TI has a similar part that has true HIZ at SHx?

0 Ryan Kehr over 3 years ago in reply to JILL LU

TI__Guru 55605 points

Jill,

No, but can you tell me why a true HIZ on SHx pins is necessary? We have a newer device like the DRV8705-Q1, but believe the behavior will be similar.

Regards,

Ryan

0 JILL LU over 3 years ago in reply to Ryan Kehr

Prodigy 10 points

Because we need a "circuit down" state so that an external circuit can take over the control to the motor/solenoid. Also because the circuit is required to use for common high solenoid.

0 Ryan Kehr over 3 years ago in reply to JILL LU

TI__Guru 55605 points

Jill,

I checked the DRV8705-Q1 and it will have the same issue. Only option would be to open up the connections to SHx during sleep state with external switches.

Regards,

Ryan

+1 JILL LU over 3 years ago in reply to Ryan Kehr

Prodigy 10 points

Yes this is can be an option. Thank you, Ryan.

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DRV8702-Q1: SLEEP MODE