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Question for TI Reference Design : AC 230V Current Controlled Solenoid Drvier with DRV 110

Inkoo Kang
Prodigy 20 points
Other Parts Discussed in Thread: DRV110, TIDA-00284, TIDA-00289

Hello,


I have a question for TIDA-00284 Reference Design with DRV110.

As my understanding, the resistor connected to HOLD pin of DRV110 used to set I HOLD current, and the equation is 150mV/R SENSE for 33.3k<R HOLD<66.6k. Because R HOLD is 51.1k and R SENSE is 4 in this design, I think I HOLD will be 37.5mA by equation. But design says I HOLD is 50mA, and graph in design shows 50mA, too.

I PEAK is also similar. R PEAK is 51.1k, and I PEAK will be 225mA by equation in datasheet. But design says I PEAK is 200mA without explanation.

In other TI Reference Design, DC24V solenoid driver with DRV110 (TIDA-00289), R PEAK and R HOLD is same to result of equation, so I'm confused. Is TIDA-00284's resistor value is just an error, or uses other equations to decide values?

  • 0
    TI__Guru** 114905 points
    Hi Inkoo,

    The authors have been contacted and should reply soon.
  • 0
    TI__Intellectual 1300 points

    Hi Inkoo,

    Thanks a lot for pointing this. This is a documentation error. The actual reference values of IHOLD and IPEAK are 37.5 mA and 225mA respectively. During testing, we got the values of approx 50mA and 200mA, which is close to the set values. This is because, at high voltage, as the duty cyclerequired is very small, the turn off time of the MOSFET and the current control delay affect the accuracy at such low currents. It depends on the solenoid parameters (L/R) also.

    Manu

  • 0 in reply to Manu Balakrishnan
    Prodigy 20 points
    Thank you for your kind answer.
    By your answer, in HOLD 37.5mA is too small duty cycle required, so current controll is not accure enough, as I undesrtand.
    But how in PEAK? Real peak current is smaller then spec, and I think in PEAK duty cycle is about 6 times than HOLD duty cycle, so it should be enough so spec should be guaranteed.

    And how can I get more accure current in LOW current? High resistance solenoid will help to solve it?
  • 0 in reply to Inkoo Kang
    TI__Intellectual 1300 points
    Hi Inkoo,

    The current-sense variation is mainly from DRV110 comparator offset voltage and reference level variation voltage.

    Since the current variation spec in the datasheet is determined with a 1-ohm sense resistor, you can find the voltage variation using Ohm’s law, then use Ohm’s law on the voltage range with the new sense resistor (example below):

    Current variation with a 1-Ohm sense resistor is +/- 30 mA (datasheet spec)
    Voltage sense variation is +/-30 mA * 1R = +/-30 mV

    With a smaller resistor, with the voltage variation fixed, the current variation would be more and vice versa. Also from the document, test results waveform, the 200mA was the avaerage solenoid peak current and you can observe that the peak current has some ripple varying between 180mA and 220mA.

    Normally the high voltgage ACsolenoids has more inductance. The solenoids with high resistance may be difficult to find. You can get more accurate hold current with a high resistance solenoid.