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BQ500101: Driving an inductive load (solenoid)

Markus Neumair
Prodigy 145 points
Part Number: BQ500101
Other Parts Discussed in Thread: DRV8844, INA200

Hello everybody,

I have to build an efficient solenoid driver according to the following specs:

- Supply voltage: 8-28V

- Output current: 3A RMS / 6A peak

- The device must not heat up to more than 40°C above ambient

- Switching frequency: 25 kHz

- Load: Solenoid with an inductance of 30mH to 500mH (yes, milli) and a resistance of at least 4Ohm

I adapted a Tina9 simulation example of the BQ500101 to these conditions. The circuit seems to work, but I'm sceptical.

Do you think the device is really capable of driving such loads in reality?

Is it possible to use low switching frequencies like 25kHz?

I know this is not an intended application of the BQ500101, but I would like to profit of the compact and efficient design of  integrated buck converters.

Most Brushed DC drivers (like DRV8844) are not capable of the required currents or produce too high power-loss...

Thanks for your replies,

Markus

  • 0
    TI__Mastermind 18200 points
    Markus,
    I am digging into this for you. Hopefully I can get you a thorough response in the next 24 hours.
  • 0 in reply to Brett Barr1
    TI__Mastermind 18200 points
    Markus,
    I just spoke to our apps experts. They said that the load type really doesn't matter, so even 500mH should be fine.

    The more critical parameter is current / loss but 3A should not be a problem at all. Neither will 25kHz.
  • 0 in reply to Brett Barr1
    Prodigy 145 points

    Hello Brett,

    that sounds really good.

    I have some further questions about this application:

    - Do you think I will face EMC-problems if the load is a few meters away from the driver? The datasheet of the BQ500101 only mentions a series resistor next to the boost capacitor to reduce voltage spikes on the switch-node.

    - Is there a limit for a minimum switching frequency?

    - Is there a compareable TI-device with protection features (especially overcurrent)? I would like to have an alternative to my current concept, BQ500101 + INA200, where the INA200 breaks the PWM input of the BQ500101 if there is an overcurrent condition.

    Thanks for your help,

    Markus

  • 0 in reply to Markus Neumair
    TI__Mastermind 18200 points
    Markus,
    It is hard to tell if you will or will not have EMC problems - this really isn't something we can predict.

    The turn on of the top FET can be slowed down by adding a boot resistor, but the turn off speed is not programmable.

    This part is typically used for sync buck converter. The switching frequency is typical above 100kHz. In DCM, the switching frequency can be down to ~100 Hz. We know the part can still work at that frequency.

    We don't have any power stage device that has OCP, this would have to come from the controller.