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I have the following motor driver (DRV8320): https://www.ti.com/lit/ds/symlink/drv8320.pdf?ts=1616576087660&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FDRV8320

Since I want to implement the deadtime compensation, I need to know what the deadtime, the on-switching time and the off switching time are, according to: https://www.nxp.com/docs/en/application-note/AN4863.pdf

Since I use the hardware variant, the deadtime is constant at 100ns, but what are the on-switching time and off-switching time? I use the Idrive in the 60/120mA mode (60mA drive, 120mA sink) and the MOSFET types are BSC0702LSATMA1 (https://www.mouser.ch/datasheet/2/196/Infineon_BSC0702LS_DataSheet-1770891.pdf) with a gate charge of maximum 11nC.

Can I say, that t_on = 11nC/60mA=180ns and t_off = 11nC/120mA = 90ns?

If so, the deadtime seems pretty neglictable, right?

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  • \$\begingroup\$ You are probably better off measuring it with an oscilloscope. You also have the MCU switch time and aliasing, current allowance, line inductance, and all sorts of stuff to consider. \$\endgroup\$
    – Damien
    Commented Mar 24, 2021 at 10:23
  • \$\begingroup\$ Switching times are interface driver and load dependent so this cannot be answered as it stands. \$\endgroup\$
    – Andy aka
    Commented Mar 24, 2021 at 10:29
  • \$\begingroup\$ Ok, I will measure with the Osci. If it is load dependet, is there a way to choose a static compensation to at least improve the performance? \$\endgroup\$ Commented Mar 24, 2021 at 10:34

1 Answer 1

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That’s not the only variable

At maximum voltage gain the 1% setting time is 1200 ns so the switching time might be 1/10 th of this or 120 ns and 100 ns deadtime will raise the driver temperature from shootthru. So choosing a lower Av setting is wise.

The other variable is the DCR of inductance and loop resistance of DCR + Ron when the other driver is switching off where T=L/R changes dynamically so the heat loss is the RMS product of that Vds(t) * I(t) * L/R as well x duty factor. A more lossy circuit is better dampened and switches faster. These are trade offs for a fixed deadtime that may be insufficient.

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  • \$\begingroup\$ Ok, you are right, so I need to increase the smart gate capability to 120mA/240mA (source/sink), that should be enough. \$\endgroup\$ Commented Mar 24, 2021 at 10:47
  • \$\begingroup\$ IDK, I used max current with slew rate control, read about that \$\endgroup\$ Commented Mar 24, 2021 at 11:19
  • \$\begingroup\$ Mhh ok, I had a ringing problem at the maximum current, that's why I reduced it. The ringing leaded even to destruction of the gate driver. \$\endgroup\$ Commented Mar 24, 2021 at 11:32
  • \$\begingroup\$ That depends on slew rate control L/R etc \$\endgroup\$ Commented Mar 24, 2021 at 11:38
  • \$\begingroup\$ I have another strange phenomena, maybe you know what could be a reason for this: The motor turns more noisy in one direction (more current peaks to keep a velocity) and more overshoot at acceleration. The electrical angle is correctly set (checked with an osci) and a SW bug in the FOC is excluded, since when I change the motor phase U and V, the motor turns better in the opposit direction as before. So can this also be a problem related to deadtime or do you have another idea, what could cause this? \$\endgroup\$ Commented Mar 24, 2021 at 12:22

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