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DRV8833: Maximum PWM frequency on xIN pins

Tim Ludwig
Prodigy 30 points
Part Number: DRV8833

Dear Support-Team,

We are using three DRV8833 motor drivers to drive an inductive load. To protect the load, we make use of the DRV8833 current chopper at 100mA (maximum rating for load). From the datasheet: 

When an H-bridge is enabled, current rises through the winding at a rate dependent on the DC voltage and
inductance of the winding. If the current reaches the current chopping threshold, the bridge disables the current
until the beginning of the next PWM cycle. Immediately after the current is enabled, the voltage on the xISEN pin
is ignored for a fixed period of time before enabling the current sense circuitry. This blanking time is fixed at 3.75
μs. This blanking time also sets the minimum on time of the PWM when operating in current chopping mode.

So, immediately after the current is enabled (meaning high level on the xIN pin?), the current on the xISEN pin is ignored for 3.75us. Does the bridge still conduct during that time? We need to drive the load at 3.9kHz with a minimum on-time of 1us.

Kind regards.

  • 0
    TI__Guru** 114905 points
    Hi Tim,

    When the outputs are enabled, the current on the xISEN pin is ignored for 3.75us. This blanking time is to prevent false overcurrent events due to capacitors on the outputs.

    We will have to confirm the device can operate with a minimum on time of 1us.
    Between 1us and 256us (~3.9kHz), does the output need to follow the input?

    The information should be available by Wednesday.
  • 0 in reply to Rick Duncan
    Prodigy 30 points
    Hi Rick,

    Thanks for your reply. What i am guessing is, although operational, the overcurrent protection will not be available when driving with 1us - 4us pulses. That would be fine though, because the overcurrent event is very unlikely to happen at that range.

    We don't have strict requirements on the delay between xIN and xOUT, so somewhere around 1-2us, as stated in the datasheet, should be fine.

    Kind regards,
    Tim Ludwig
  • 0 in reply to Tim Ludwig
    TI__Guru** 114905 points

    Hi Tim,

    Thanks for the additional information.

    You are correct; the overcurrent protection is not available if you disable the device in the 1 to 4us range. As you stated this should not be a problem.

    There will be some uncertainty between the input pulses and the output pulses. A quick check of the outputs shows the output pulse is ~300ns +/- 100ns longer than the input pulse.

  • 0 in reply to Rick Duncan
    Prodigy 30 points

    Hi Rick, 

    Thank you very much for your support. Will the stretching of the output pulse occur over the full range, or is it limited to the 1-4us range?

    Kind regards,

    Tim Ludwig

  • 0 in reply to Tim Ludwig
    TI__Guru** 114905 points
    Hi Tim,

    The stretching is over the full range.