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TPS51604 or MOSFET issue

BO
Genius 12760 points
Other Parts Discussed in Thread: CSD87335Q3D, TPS51604

We use 3-half bridges to drive three phase motor with the configuration:

 

Driver TPS51604 + CSD87335Q3D

 


Problem description (the problem occurs only sometimes):

  1. After power switch on the driver low output is LOW (measurement with oscilloscope) although the PWM input is LOW (initial state after power on, SW ).

  2. After activating the PWM (50/50) the driver output LOW remains LOW (doesn’t follow the PWM signal).

  3. If we measure the driver high output (we don’t know the status before measurement) or the switch node the problem is solved, all the signals are OK. The driver high output

 

We measured the +5V and PWM input seems to be good. We analyzed the driver logic function (Table 1) but couldn’t find any reason causing the problem.

 

 

We assembled other resistor values on low gate (5Ohm) high gate (10Ohm of the MOSFET but didn’t help.

We assembled other capacitance value as bootstrap (1μF) but also didn’t help.

We assembled a resistor of 100kOhm between SW node and GND which eliminates the problem, as expected because the measurement with the oscilloscope on SW node helps too.

In the previous design we use the Vishay transistors (SI7228DN) and never had such a problem.

The failure only appears sometimes at startup, not during normal operation.

 

Regards,

Bernd

  • 0
    TI__Mastermind 24075 points
    Hi Bernd,

    What's Vout, 7.5V?
    Can you check the boot capacitor voltage when the issue occurs?

    Thanks
    Qian
  • 0 in reply to Qian Chen
    TI__Intellectual 800 points

    Hi Dear user,

    TPS51604 was not designed or intended to be used for Motor Control applications. This IC works well for Computing aand VR platforms where the Input PWM signal comes from a matching outputs tri-state controller.For the driver IC TPS51604 to un-latch prior to start-up, proper input PWM sequence needs to be  supplied.

    We recommend a 10..22kOhm pull-down resistor from CSD87335 Switch-Node pin to Ground.

    This resistor would not affect the System power Loss and Efficiency, but will provide a path for the Bootstrap Cap charging during the initial PWM pulse.

    Charging the Bootstrap Cap is a condition necessary to happen prior to the first tri-state to High PWM transition so the Internal TPS51604 Bootstrap FET is enhanced. In this way we can obtain the first pulse on PWM HS output. As a result, the CSD87355 will start switching thus obtaining correct PWM pulse outputs.

    Best Regards.

  • 0
    TI__Genius 12760 points

    Hi Lucian

    thank you for your comprehensive feedback.

    Customer found another solution using SKIP pin to wake up the driver.
    The question is here, is it OK to use the SKIP pin for driver wake up or is it better to use the recommendation with the pull-down (10…22kOhm) at SW node.

    They tried driver wake up doing the following:

      • Pull-up of 10kOhm on SKIP pin
      • After start-up when the DSP runs using GPIO get the SKIP pin to LOW for about 1ms
      • Set SKIP pin again to HIGH

    Regards,
    Bernd

  • 0 in reply to BO
    TI__Genius 12760 points

    Hi Lucian,

    can you comment if it is OK to use the SKIP pin for driver wake up or is it better to use the recommendation with the pull-down (10…22kOhm) at SW node.

    Regards,
    Bernd

  • 0 in reply to BO
    TI__Intellectual 800 points
    Both proposals the Skip pin use or the 22k Vsw resistor work fine.
    Use the SKIP method to wake up the chip and unlatch if you have already the board working and you don't have the time or resource to modify the layout.
    Best luck,
    Lucian