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ISO5452: FLT signal turn low when the device is working

Minghao Yin
Prodigy 365 points
Part Number: ISO5452

Hi Team,

Customer use 3 pcs ISO5452 in a 380V/7500W servo system. The use ISO5452 as a gate driver to control the U/V/W high side IGBT, and they use Opto-Coupler for the low side gate driver. 

The ISO5452 each use an independent power supply(+16V/-8.2V). And the Opto-Coupler have the same power supply.(+16V/-8V). When the servo system start working, the device U31 FLT will turn low. And the D67 will turn on. 

The frequency of the noise in the above picture is the same as the carrier frequency of PWM. A single noise is about 680ns.

During the actual test, D46 and TVS18 were not used because the junction capacitance of the selected device was a bit large and suitable Schottky tubes and voltage regulator tubes were not available yet.

This is the PCB Layout. Please help analyze whether the problem is caused by the layout, and provide guidance on how to optimize it, thank you.

  • 0
    TI__Genius 13650 points

    Hi Minghao,

    The gate driver FLT pin should only be going low when the voltage on the DESAT pin has exceeded the DESAT pin feature voltage threshold(9V) for longer than the DESAT de-glitch filter(330ns).

    I have a couple questions to help with the investigation:

    • When they run tests do they have MOSFETs connected to the board?
      • If there's no MOSFETs connected to the board the cathode of D70(DESAT HV diode) would be left floating allowing gate driver internal current source to charge up the external DESAT blanking capacitor up to the threshold and shutdown the gate driver.
    • What kind of tests is the customer running in the system?(e.g. double pulse test, fully assembled system operation, short circuit testing, etc...)
    • Has the customer monitored the voltage on the DESAT pin to see what is happening to the voltage on that node?
      • Would like to confirm if the voltage on this node is rising.
    • What gate driver signals were probed on the waveform on the post?(e.g. VCC2 referenced to GND2, GND2 referenced to GND1, etc...)

    Best regards,

    Andy Robles