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DRV8800 ENABL terminal

NAOKI AOYAMA
Guru 11215 points
Other Parts Discussed in Thread: DRV8800

Hello,

Our customer uses the DRV8800.

There are some noise at high current condition (about 1.5A).
The noise effect malfunction of ENABLE pin, stop the motor sometime.
So, the customer has some questions.

1.)How much the minimum Low time of the ENABLE operates the device disable?

2.)How much the value of the internal pull down resistor on ENABLE pin?

The customer uses the external pull up resistor at ENABLE pin.
That is more sensitive to malfunction by noise. But the customer
follow the TI's recommendation as below.

on datasheet  P11  9.3.1 Logic Input

" TI recommends using a high-value pullup resistor when logic inputs are 

 pulled up to VDD."

Should the customer use a pullup resistor?

In the case of  the customer pull up ENABLE pin to VDD without resistor,

there is no malfunction.

Regards,

Naoki Aoyama

  • 0
    TI__Guru** 114905 points
    Hi Aoyama-san,

    What value pullup did the customer use? What is the pullup voltage?

    The recommendation is intended to limit current, but also expects the voltage to be above the Vih threshold of 2.0V. In general, I would target a pullup resistor that sets the voltage at 3V or above. This will provide more margin.

    In many cases, the ENABLE input is connected directly to a GPIO. The GPIO disables the outputs when the motor is not operating.


    Answers to your questions.

    1.)How much the minimum Low time of the ENABLE operates the device disable?

    This will require investigation to find the time. Please let me know if this is still required.

    2.)How much the value of the internal pull down resistor on ENABLE pin?

    The pulldown resistor can be as low as 20kOhm, but is typically 50kOhms. This can be determined dividing VIN by IIh max for the ENABLE pin.
  • 0 in reply to Rick Duncan
    Guru 11215 points
    Hi Rick-san,

    Thank you for your fast reply.

    The customer used 3.3kOhm for pull-up resistor.
    The pull-up voltage is 5V.

    About question 1)
    The customer will use the DRV8800 for various applications.
    So the customer wants to know the value for the circuit design notes.
    Could you give me the value?

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Guru** 114905 points
    Hi Aoyama-san,

    A 3.3kOhm pullup to 5V should provide at least 4V at the ENABLE pin. This is well above the minimum Vih threshold of 2V.
    Is the 3.3kOhm pullup connected to multiple inputs pins?

    If possible, please ask the customer to measure the voltage at the ENABLE pin with the 3.3kOhm resistor to 5V.

    What is meant by "the value for the circuit design notes"?
  • 0 in reply to Rick Duncan
    Guru 11215 points
    Hi Rick-san,

    Yes, the 3.3kOhm pullup connected to nFAULT pin together. Not input pin.
    The voltage at the ENABLE pin is 4.7V.
    Usually, the DRV8800 works normal operation. But a noise (perhaps external PWM signal noise)
    get into this line, the motor stop sometime.
    The customer measure the noise time, that is less than 1usec.
    So the customer wants to know that the ENABLE operates the device disable under
    less than 1usec Low time.

    Regards,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Guru** 114905 points

    Hi Aoyama-san,

    Determining the minimum pulse width on ENABLE may take some time. We will investigate and provide a typical time as soon as possible.

    Is it possible to send:

    1) the schematic around the DRV8800
    2) scope captures of the noise event on ENABLE
    3) scope captures of the nFAULT output during the noise event

  • 0 in reply to Rick Duncan
    Guru 11215 points
    Hi Rick-san,

    Thank you for your fast reply.

    I'm sorry but the customer can not open the circuit.
    May I send you the circuit by E-mail?

    Thanks,
    Naoki Aoyama
  • 0 in reply to NAOKI AOYAMA
    TI__Expert 5285 points

    Hello Aoyama-san, Rick-san,

    Allow me to jump into this topic. I am working with Aoyama-san for this issue.
    As Aoyama-san mentioned, we need to talk on the email about more detail.
    Rick-san, I will send you an email later.

    Best regards,
    Shinya Sawamoto