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Original question:

DRV8873: OUT2 and IPROPI2 when not used

DRV8873: OLD when having a unused output at Independent Half bridge

Yusuke Mukuno
Expert 7395 points
Part Number: DRV8873

Hi expert,

My customer is considering DRV8873 for 2 solenoids drive by Independent Half bridge,

They have the case of 1 solenoid per 1device. 1output is unused.

I found the following E2E session.

However, my customer would like to use OLD(open load detection).

If OUTPUT2 is floating, they cannot monitor OLD of OUTPUT1, right?

Do have any advice for using OLD at only 1output at Independent Half bridge?

Customer use case (connection) : VM > driver(DRV8873 high side) > solenoid > GND

Thanks

Muk

  • 0
    TI__Guru 56650 points

    Mukuno-san,

    Open load detection supports both passive load detection OLP when DISABLE pin is high or active load detection OLA (DISABLE pin is low and the motor is energized.

    For OLP, both pullup and pulldown comparators need to be high to report OLD. Customer case works. (connection : VM > driver(DRV8873 high side) > solenoid > GND)

    For OLA, In independent PWM mode, the motor can enter the brake state either by high-side or low-side recirculation. If the motor enters the brake state using low-side recirculation, the diode VF voltage of high-side FET is less than the VOLA voltage which flags an open load fault even though the load is connected across the OUT1 and OUT2 pins. In this case, the OLA mode should not be used. If high-side current recirculation is done with independent PWM mode, the OLA mode functions properly.

    Customer case  (connection : VM > driver(DRV8873 high side) > solenoid > GND) uses the low-side recirculation. The OLA mode should not be used.

    Does the customer use DRV8873H or DRV8873S?

    In the hardware version of the device (DRV8873H), OLA mode is active when the nOL pin if left as a no-connect pin or tied to ground. If low-side current recirculation is done with independent PWM control, an open load condition is detected even though the load is connected. To avoid this false trip, the OLD must be disabled by taking the nOL pin high; however, both OLA and OLP diagnostics will be disabled.

    For SPI version device DRV8873S, customers can use SPI command to enable or disable the open load detection function.