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TPS40170 issue

Other Parts Discussed in Thread: TPS40170, CSD19532Q5B, CSD18537NQ5A

I’m fighting an issue with the TPS40170 part. Our prototype first used 4 of the Infineon IPB107N20NA and the prototype worked well. I then switched the FETs over to 2 of the Infineon IPW65R045C7FKSA1. The top side FET was really hot as well as the regulator. I powered down the system and powered on again but the regulator only got hot and would not control the gate of the FETs. I tried the TO-220 version of the IPB107N20NA (IPP110N20NA) but the regulator once again failed to regulate. I connected 4 of the IPP110N20NA to the circuit (2 in parallel) and found that the regulator could go up to a small output wattage (~20W) but the part was very hot and the soft start pin was ramping up and down, indicating either a high current or over temperature event. Do you have any advice? Are the FETs I’m selecting not appropriate for the device? I know the development boards use the CSD18537NQ5A FETs. I tried using 2 of the CSD19532Q5B but that too caused damage to the regulator. 

  • Hi Jaden,

    It is very likely the TPS40170 is overheating due to the high gate charge of these MOSFETs. With 4x IPP110N20NA the gate charge current is IGC = 4 x 53nC x fsw. The power loss in the IC is then (VIN - 8 V) x IGC.

    What input voltage and switching frequency are you testing with? Does the circuit work better if you reduce switching frequency or reduce the input voltage?

    Best Regards,
    Anthony