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Original question:

DRV8702-Q1: DRV8702-Q1

DRV8705H-Q1EVM: Switching losses

Federico Silva
Intellectual 795 points

Part Number: DRV8705H-Q1EVM
Other Parts Discussed in Thread: CSD18512Q5B

Hi,

I have an evaluation board which I'm supplying at 20V, on which I want to evaluate switching losses for this driver.

Firstly, in idle state (driver on, not switching), I have a power consumption of 0.3 W. When I inject a 100 kHz square wave at 50% duty cycle on each input of each half bridge (independent half bridge mode), the total losses without any load, are 1.5 W. This consumption seems to be fairly big, even more so if I compare with what I'd expect for this mosfets. If I'm correct, the switching losses are given mainly by (full bridge)

Pgate = 2 Qgate*Vsupply*fsw

Psw = Qo*Vsupply*fsw + Qrr*Vsupply*fsw

Given the mosfet used on the evaluation board (CSD18512Q5B), I compute the losses to 0.39 W, which are far off what I see (1.5 W-0.3 W=1.2 W). What am I missing? Are those formulas wrong?

Thanks,

  • 0
    TI__Mastermind 48925 points

    Hi,

    My first impression is 100KHz is very high frequency for motor driving and normally we do not test. Are you considering to use DRV8705H-Q1 for motor driving and testing DRV8705H-Q1 EVM with 100KHz? 

    With 20V and 100KHz, I guess FET switching loss could be some amount of portion. I am wondering you have some load (e.g capacitor, resistive load) on FET output.

    regards

    Shinya Morita