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TPS40170-Q1: 3.3V voltage output is not stable

neeraj kaushik
Prodigy 10 points
Part Number: TPS40170-Q1
Other Parts Discussed in Thread: LM25116, TPS40170

Hi ,

 I Have used TPS40170QRGYRQ1 in one my new prototype design where the i/p is between 5V to 30V and o/p required is 3.3V @15A (max), 8 A(typical), 4A (min). 

 I have referred the design generated by the TI's Webench tool. Reference design and actual design schematics are attached herewith.

 When powering the board with 12V supply, the o/p seen on the 3.3V is not stable and shows lot of switching from 2.6 V to 3.8V. i have taken the waveforms at inductor switching side, o/p Cap which are attached herewith.

  Please help me in getting this issue resolved.

  • 0
    Prodigy 10 points

    Updated Circuit attached where C1710 and Q1607 parts are updated. the waveforms above are actually taken with this circuit.

  • 0 in reply to neeraj kaushik
    TI__Mastermind 46061 points

    Hello Neeraj

    The frequency of the output voltage ripple is 60-70Hz / 120-140Hz which cannot be generated from the device itself. 
    I think you have to monitor the load current which might be 60-70Hz / 120-140Hz pulsating load. Also you have to check the signals which are provided by an external source (for example, VSYS, 3V3_EN_SWITCH, VDDA_1V8, DCDC_3V3)

    -Eric Lee (Applications Engineering)

  • 0 in reply to EricLee
    Prodigy 10 points

    Hello Eric,

    Thanks for quick reply.

    VSYS is clean. does not have any switching freq on it. the same supply VSYS is being supplied to 5V o/p regulator on board i.e LM25116 which is generating o/p properly.

    3V3_EN _Switch is just coming from SW701 on left  which is simply to PD the EN pin to GND in order to switch off the 3V3 o/p. 

    VDDA_1V8 will be generated once we have stable 3.3V. thereby VDD_3V3 will not be ON untill be have VDDA_1V8.

    DCDC_3V3 is output of TPS40170 which will be supplied to PMIC on the Board which is presently not mounted on board. thereby 

    To rule out the pulsating load issue. i have connected an external variable 3.3V supply to board at C709 (by removing HS/LS MOSFETs and not supplying VSYS. the board works fine and do not show any switching on 3.3V.

    Need your guidance if you want me look into any other particular signal.

    Thanks

    Neeraj

  • 0 in reply to neeraj kaushik
    TI__Mastermind 46061 points

    Hello Neeraj 

    Do you mean the board works fine without any issue by connecting an external 3.3V supply to C709 ? 

    If you still have an issue, please send me some zoom-in waveforms when the VOUT shoots up. including SW, inductor current , COMP, VOUT 

    -Eric Lee

  • 0 in reply to EricLee
    TI__Mastermind 46061 points

    Hello Neeraj 

    I will close this thread since no activity for a week. Please submit a new request if any more question. 

    - Eric Lee ( Applications Engineering)