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DRV8955: DRV8955 Options

Sam Selyutin
Prodigy 120 points
Part Number: DRV8955

Tool/software:

Hi All,

I'm looking to use the DRV8955 to drive a solenoid valve open and closed as quickly as possible. I would also like to utilize the ITRIP feature to limit the current from exceeding a threshold, as well as use PWM to bring the average current to a much lower value to keep the valve in the open position.

I have seen many configurations for this:

1) High and low-side drivers (single transistor)

2) Half-bridge

3) Full-bridge (H-bridge)

To my understanding, is 3) H-bridge the only configuration in which I can decay the field in the solenoid the quickest? My concern when using this option is to reverse the field such that the solenoid valve re-opens. Is there a way I can configure the fast decay mode to switch to Hi-Z / open the two FETs operating in the fast decay when my current is close to 0A? Is this something I can configure with this chipset?

Otherwise, I would have to calculate / measure the approximate time in which the fast decay mode needs to be turned off. I have seen other chipsets with this feature that will automatically enter a Hi-Z mode in order not to reverse the field. In the application of a motor, the field reversal would cause it to begin spinning in the other direction and with a solenoid valve, it would just open the valve again when the current crosses over the 0A threshold.

Any advice here would be helpful! Thanks in advance.

  • 0
    TI__Mastermind 28695 points

    Hi Sam,

    Thank you for posting in this forum. I assume you were referring to the decay feature mentioned in page-14 of the datasheet, see below. The fast decay here refers to the bridge going to Hi-Z and recirculation current flowing through body diodes. In this mode the bridge will be in HiZ as long as PWM  is 0. The recirculation current is dissipated via body diodes until the energy is dissipated. Slow decay has recirculation current via FETs during PWM = 0. This mode will be present as long as the PWM = 0. To release it you may have to make EN1 = 0 after the desired time. Thank you.

    Regards, Murugavel

  • 0 in reply to Murugavel4637
    Prodigy 120 points

    Thanks for the reply!

    I was wondering about the following case:

    Source: AN:SLVAE59A - Using Motor Drivers to Drive Solenoids

    The fast decay I am describing is (2) in the above figure 2-7. I am not sure why it would be called "Reverse PWM" if in reality the FETs themselves are turned off. Do you mind elaborating on this slightly?

    I am worried that if I only rely on the Body Diodes for current decay, my solenoid valve will not close as fast as desirable. I understand I can also add a Zener in parallel with an additional fast switching diode to increase the current decay as follows:

    Thanks,

    Sam

  • +1 in reply to Sam Selyutin
    TI__Mastermind 28695 points

    Hi Sam,

    The DRV8955 bridge control logic does not do bridge reversal type of fast decay. It does a Coast Operation type Fast Decay.

    Sam Selyutin said:

    I am worried that if I only rely on the Body Diodes for current decay, my solenoid valve will not close as fast as desirable. I understand I can also add a Zener in parallel with an additional fast switching diode to increase the current decay as follows:

    That's a valid concern. With external control logic from an MCU you can perform a bridge reversal for a short period of time to rapidly decay the energy in the solenoid for closing the valve. 

    Regards, Murugavel

  • 0 in reply to Murugavel4637
    Prodigy 120 points

    Hi Murugavel,

    I appreciate you taking the time to let me know! I misunderstand the datasheet. Looks like I'll have to find an alternative IC to perform this task - perhaps the freewheeling operation will work to decay the field fast enough. Won't know until I test with the real valve.

    Thank you!