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TPS65982: Q2 MOSFET Burnout issue

Kai Hsiao
Guru 12675 points
Part Number: TPS65982

Hi Sir 

Green waveform is DC_IN

Yellow waveform is PD_OUT

Purple waveform is Vgate 

Blue waveform is Iout 

Please refer below waveform and schematic ,when we test PD_OUT SCP (short current protection) ,Q2 MOSFET will be burnout 

Figure 1. When the PP_EXTOCTimeout set 5.12mS ,Vgate can't turn off and Q2 burnout 

Figure 2. When the PP_EXTOCTimeout set 640uS ,Vgate can turn off but need 1mS 

Q1 : May I know why 5.12mS can't turn off the MOS? and Vgate have a short time pulse ?

Q2 : May I know what's the PP_EXTOCTimeout means? OCP dection time ? or retry timer ?

  • 0
    TI__Mastermind 36751 points

    Hi Kai,

    When you have the external OCP timeout set to 5.12ms, the FET will need to be able to absorb close to 100W of power (20V, 5A) with VDS =20V (VBUS =ground). There are not many FETs available on the market that have such a strong SOA curve to handle that much power for such an extended period of time. Instead, we recommend setting this to 640uS and checking to make sure your FET will be able to handle VDS=20V and IDS=5A for up to 1.5ms. When selecting the 640uS timeout value, the real value is a range from 640uS to 1.3mS. You said it takes 1mS to turn off the FET. This is in the range of the specification.

    If this answers your question, PLEASE select This resolved my issue

    Thank you,

    Eric

  • 0 in reply to Eric Beljaars
    Guru 12675 points

    Hi Eric

    Sorry!! this is a urgent case 

    We meet Q2 MOSFET burnout issue 

    I saw F/W user guide could modify timeout setting from 640us to 160us

    But the latest config tool version 3.18 can't change to 160uS (the minimum setting is 640uS) 

    Could you help to support this case ?

    Thanks

  • 0 in reply to Kai Hsiao
    TI__Mastermind 36751 points

    Hi Kai,

    We do not recommend a setting lower than 640uS as it could cause false OCP trips on the external path when there is a small glitch in the current. Instead, we recommend using an external FET with SOA curve suitable for this application. You can refer to the datasheet of CSD16323 for an example of a recommended external FET.

    If this answers your question, PLEASE select This resolved my issue

    Thank you,

    Eric

  • 0 in reply to Eric Beljaars
    Guru 12675 points

    Hi Eric

    I saw our end customer have already discuss this issue with you

    If I provide the PJT file to you ,could you help to change the time to 160uS and provide the bin file to us ??

    Attached file is the PJT file 

    UCC7_V3_10_V1.12_06_20180611.rar

  • 0 in reply to Kai Hsiao
    Guru 12675 points
    Hi Eric

    Looking forward your reply
  • 0 in reply to Kai Hsiao
    TI__Mastermind 36751 points
    Hi Kai,

    I have discussed this issue with your end customer. We recommend using a bigger FET since the 160uS timeout value will trip the OCP too fast and cause unwanted disconnect/reconnect.

    Thank you,
    Eric