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LM5060: Q1 MOSFET Failure in Reverse Polarity Protection with Diodes (fig. 39)

Part Number: LM5060
Other Parts Discussed in Thread: DRV8323, CSD88599Q5DC

Hi,

I used LM5060 to implement protection circuit for OV, UV, OC & reverse polarity protection on BLDC motor PVDD. I used DRV8323 for driving BLDC motor. PVDD is 24V. 

As a reference for protection circuit, I have taken fig. 39 (Application with Reverse Polarity Protection with Diodes for OUT Pin Protection). I also have a provision of turn-On delay capacitor (DNP) mentioned in Fig. 28.

I connected two 390uF, 50V bulk capacitors on PVDD near H-bridges. 

My concerns are:

1.  Druing testing i observed that MOSFET Q1 (in fig. 39) getting damaged. Gate and drain is getting shorted. MOSFET part that i used is IRFB7440PBF. I want to know the probable reason behind the failure and update design. Please suggest me.

2. Also as mentioned in section 8.2.2, D5 & D7 are only necessary if the output load is highly capacitive.In our design two 390uF is used as bulk cap and also motor is having phase inductance of 131uH. I want to know what load shall be considered as highly capacitive? If two 390uF capacitor is not high then shall i remove it from board?

3. If the load capacitance (390uF + 390uF) is large, then should i have to connect current limiting resistor Ro as mentioned in section 8.2.1.2.9 ?

Regards,

Amit

  • Hi Amit,

    Can you please share complete schematic. Does the MOSFET failure happened during start-up or in running condition? Is the controller LM5060 fine?
    Can you share a test waveform of Vin, Vout, Input current and GATE voltage for LM5060 device.

    Best Regards,
    Rakesh
  • Hi Rakesh,

    I am not able to share the complete schematic but i am sharing part of it (Protection Circuit, DRV8323 section & H-Bridge Section). Hope it will give you fair idea. The operating voltage is 24V from Lead Acid Battery.

    The failure is not happening during startup or even during continous running. It happended very randomly. Also as i mentioned, we are running motor at no-load and current consumption is ar

    Rakesh said:
    Hi Amit,

    Can you please share complete schematic. Does the MOSFET failure happened during start-up or in running condition? Is the controller LM5060 fine?
    Can you share a test waveform of Vin, Vout, Input current and GATE voltage for LM5060 device.

    Best Regards,
    Rakesh

    ound 2.2A from power supply. The power supply that i am using is having 5A current limit.

    LM5060 controller is fine. When i replaced MOSFET Q1, again circuit is working fine. No other failure observed on protection circuit.

    Kindly do the needful.

    Regards,

    Amit

  • Hi Amit,

    The schematics gave good understanding on how you are using the device. Thanks for the details.
    Can you share a test waveform of Vin, Vout, Input current and GATE voltage for LM5060 device to analyze the stress on MOSFET Q1 during startup. I see, 380uF x 2 caps at the output, which causes inrush current and stress on MOSFET Q1.

    Best Regards,
    Rakesh
  • Dear Rakesh,

    Below are test waveforms of Vin (VBAT- YELLOW), Vout (PVDD-GREEN), Input Current (Current- PINK) & GATE Voltage ((GATE-BLUE). While capturing waveform i used CC-CV power supply. Power supply voltage is set to 24V and current is set once to 5A & once to 25A. We observed failure failure when we worked with power supply current limited to 5A. I captured waveform with 25A current limit to simulate as if connected to battery (no current limit, current only limited by LM5060).

    Waveform with power supply set to 24V & 25A current:

      

    Waveform with power supply set to 24V & 5A current:

    Could you please suggest at the earliest.

    Regards,

    Amit

  • Hi Amit,

    Thank you!
    Can you repeat second test (power supply set to 24V & 5A current) without 380uF x 2 caps at the output.

    These waveforms are at no-load. Is it close to the actual scenario? I mean, you will enable the BLDC motor only when the LM5060 powers up the output?

    Best Regards,
    Rakesh
  • Hi Amit,

    Any update?
    We can have short call to discuss.

    Best Regards,
    Rakesh
  • Hi Rakesh,

    I have not repeated 2nd test (24V & 5A) without 380uFx2. As of now, failure of Q & Q3 (IRFB7440PBF) but now we are having failure issues with U4,U5 & U7 (CSD88599Q5DC). So we are breaking head on this now. It will be really helpful if you support.

    All waveforms captured at no-load. In actual scenario, we will enable BLDC motor only after LM5060 powers up the output.

    Yeah, we can have a quick call to discuss this. You can give me a call on +91-8373911802 or give me your number, I will call you.

    Regards,

    Amit

  • Hi Amit,

    As discussed over call, do test as soon as you get new boards and please post a new/related thread.
    As it will take sometime, please close this thread.

    Best Regards,
    Rakesh