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DRV110EVM: The current decreases very slowly after disable

Antonello Lombardinilo
Prodigy 30 points
Part Number: DRV110EVM
Other Parts Discussed in Thread: DRV110

Hi team,

I am using the DRV110EVM to drive a solenoid pump. The power supply is about 26Vdc and I have configured the EVM to have an Ipeek of 2A and Ihold of 0.7A.
The enable signal on JP9 is a PWM 0..3V3 with a period of 600ms and Ton of 100ms.
The waveforms I get are attached (yellow OUT, purple Solenoid current).
I don't understand why the current decreases very slowly after the enable signal go to GND.

Can you help me understand and solve?

Thanks

Antonello

  • 0
    TI__Expert 4940 points

    Hi Antonello,

    1)Seems to me the 26V doesn't have enough headroom due to high solenoid R and L? What are solenoid R and L?

    2) Did you changed EVM Rsense? for Ipeak/Ihold=2/0.7A Rsense should be <=0.21ohm

    Regards,

    Costin

  • 0 in reply to Costin Cazana
    Prodigy 30 points

    Hi Costin,

    R=7,3Ohm and L=13mH. DCSUPPLY=26V

    I changed the Rsense to 0,1ohm. I also replaced Q2 (and F1 fuse) with STD20NF06LT4 to have more current.

    If I drive the solenoid in "on/off" mode without using the DRV110 I get the waveforms shown in the following figure (yellow: mosfet enable, purple: solenoid current, blue: sensing current ar mosfet source on 0,05 Ohm)

  • 0 in reply to Antonello Lombardinilo
    TI__Expert 4940 points

    Hi Antonello,

    Based on current slew rate solenoid R and L seems to be higher.

    Due to this slow current slew rate,  the set Tkeep( peak time) is short, current just reaches 2A at the end of peak time.

    The supply voltage needs to be increased to speed up solenoid current.

     Most of Ton is used by peak current, not too much power saved. Based on picture Tpeak is 70mS and Thold is 30mS.

    If Rsense=0.1ohm:

    Rpeak=300kohm for Ipeak=2A

    Rhold=142kohm for Ihold=0.7A

    Regards,

    Costin

  • 0 in reply to Costin Cazana
    Prodigy 30 points

    Hi Costin,

    thanks for the reply.

    What I do not explain, however, is the current trend when the DRV110 is "disabled" (EN pin to GND).

    The current after the Tpeek decays very quickly, while, after the hold phase, when the DRV110 is disabled, the current decreases very slowly.

    But this only happens using the DRV110EVM and is in contrast to what I see in the image of my second post.

    Regards,

    Antonello

  • 0 in reply to Antonello Lombardinilo
    TI__Expert 4940 points

    Hi Antonello,

    DRV110 controls just the FET gate, sink/source current up to 10mA. Otherwise that's no difference compare to an external gate control

    One suggestion is to monitor the gate voltage/current, DRV110 En=Off turns off the gate voltage.

    Regards,

    Costin

  • 0 in reply to Costin Cazana
    TI__Expert 4940 points

    Hi Antonello,

    One difference between these two experiments ( FET driven with/out DRV110) is the gate voltage:

    -DRV110 : 15V

    -external : 3V

    The solenoid current turn_on/turn_off is set by the FET and solenoid parameters, DRV110 just toggle the gate of the FET 

    Regards,

    Costin