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DRV8770: DRV8770

sapana darekar
Prodigy 20 points
Part Number: DRV8770

Tool/software:

I am using DRV8770 for Relay driving. Do we need to charge Bootstrap capacitor externally. If not, then how should I configure the IC to charge the Bootstrap capacitor to operate high side MOSFET.

  • 0
    TI__Expert 6130 points

    As bootstrap cap is charged thru the low side FET, so 100% duty cycle is not supported on this device.  At least some low-side switching is required to keep cap charged. How to calculate worst case frequency & Ton needed to turn on low side fet?

    For relay kind of pure ON/OFF application (with 100% duty cycle), which device do you recommend?

  • 0 in reply to PRAHLAD Supeda
    Prodigy 20 points

    H bridge Low side MOSFET should we used to charge the Bootstrap capacitor, or another charging circuitry is required? For relay coil PWM (total duration On-OFF 2-4msec).latching relay.

  • 0 in reply to sapana darekar
    TI__Mastermind 40195 points

    Hello,

    sapana darekar said:
    I am using DRV8770 for Relay driving. Do we need to charge Bootstrap capacitor externally. If not, then how should I configure the IC to charge the Bootstrap capacitor to operate high side MOSFET.

    Please follow the application schematic is section 8.2 Typical Application of the datasheet, page-14. Another charging circuitry is not required. The bridge must be driven by PWM inputs with < 100% duty cycle, else the bootstrap will not work and result with Gate Driver Supply undervoltage lockout (GVDDUV) will happen. 

    PRAHLAD Supeda said:
    As bootstrap cap is charged thru the low side FET, so 100% duty cycle is not supported on this device.  At least some low-side switching is required to keep cap charged. How to calculate worst case frequency & Ton needed to turn on low side fet?

    Please refer to section 8.2.1 Design Requirements of the datasheet, page-15. Once you calculate and decide on the capacitor value you can determine the capacitor charge time (tON for LS-FET) required to charge it fully by using R (Rdson of LS-FET), CBSTA/B and GVDD voltage. For 100nF you may need around 50 to 100 ns approx.

    PRAHLAD Supeda said:
    For relay kind of pure ON/OFF application (with 100% duty cycle), which device do you recommend?

    What are the operating voltage and current requirements? PWM control requirement? Frequency and duty cycle range? Current regulation required or not? Current sensing requirement? etc. Thank you.

    Regards, Murugavel