DRV8885 Logic Input impedance when VM=0V

NAOKI AOYAMA

Guru 11215 points

Other Parts Discussed in Thread: DRV8885

Hello,

Our customer uses the DRV8885.

The customer operate MCU before the DRV8885 operate.

The customer wants to know the impedance of the logic input pins when the VM=0V.

Could you tell me the impedance of STEP, DIR, ENABLE,M0, M1, DECAY, TRQ, nSLEEP pin

when the VM=0V ?

When the VM=0V, the DVDD regulator is shut down. How about the voltage of the RREF pin?

Regards,

Naoki Aoyama

over 9 years ago

0 Wilson Zuo over 9 years ago

TI__Mastermind 26065 points

Hi Naoki,

It may be different with VM open or VM = 0V. If VM open, the PD resistor of normal inputs will be about 100k and the tri-state inputs will be about 32k.
Some supply will short the output so that VM = 0 means the VM almost short to GND. In this case, the inputs impedance could be lower. The tri-state inputs could be about 20k.

We will test the RREF voltage and get back later.

Best regards,

0 NAOKI AOYAMA over 9 years ago in reply to Wilson Zuo

Guru 11215 points

Hi Wilson,

Thank you for your fast reply.
I understood the normal inputs and tri-state inputs.
How about the DECAY input? Refer to the Figure 24, there is a current source as 20uA.
If the current source is shut down, there is only a reverse diode. Is the DECAY input Hi-Z?

Best Regards,

Naoki Aoyama

0 Wilson Zuo over 9 years ago in reply to NAOKI AOYAMA

TI__Mastermind 26065 points

Hi Naoki

Yes. The DECAY and RREF has about 500k input impedence when the device is not powered.

Best regards,

0 NAOKI AOYAMA over 9 years ago in reply to Wilson Zuo

Guru 11215 points

Hi Wilson,

Thank you for your reply.
I will feedback the customer this information.

Very Thanks,

Naoki Aoyama

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DRV8885 Logic Input impedance when VM=0V