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TPS54326: Powering issue

Pradeep Kumar68
Intellectual 420 points
Part Number: TPS54326

HI TI,

We are using TPS54326PWPR in our telemetry application. This IC is used to convert 16V into 5.5V. Schematic is attached for your reference.

The problem we are having is,

1.) If we connect 16V into Lab power supply and switches on power supply then DC-DC converter is not giving 5.5 V output voltage.

2.) If we power on supply first and then if we connect 16V into power supply then it works fine

3.) We have checked with different power supply from different makes but the issue remains the same

4.) This issue remains the same with or without load

5.) I have tried with 0.01uF soft-start capacitor( 3.8ms soft-start time) but the issue remains the same

6.) If we make soft-start capacitor to 0.1uF ( 38ms soft-start time), then everything works fine. But our requirement is to have less than 5ms soft-start time.

Please let us know if we making any mistake and help us in overcoming this issue.

  • 0
    TI__Genius 15135 points

    Hi, Kumar   

    I think it was caused by Vin slow rising up. 

    When Vin > UVLO wake up threshold, IC starts to work, and try to regulate Vout to target voltage(5.5V) after soft start time.

    When soft start ends, UVP function will be active, if Vin rises up too slowly, and Vout is below UVP threshold, IC will be shut down and latched off by UVP function. (You can refer the UVP function in datasheet of page8). 

    So please use a fast Vin power supply to test again.  

  • 0 in reply to Zhao Ma
    TI__Guru**** 191445 points

    Zhao is most likely correct about your start ups issue.  We have seen this in previous cases.  I have another unrelated comment about your schematic.  TPS54326 uses DCAP2 control mode and is deigned to use 22 uF to 68 uF of ceramic output capacitance.  I see you have 100 uF electrolytic as well.  I have personally tested TPS54326 with additional electrolytic capacitor up to 220 uF.  It may work for you but it will depend on the ESR  You should check the ESR zero and compare to the feed forward zero/pole pair.  It would also be advisable to check the overall loop stability.