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TPS65218: PMIC output toggle and become zero at PB button push time

Santosh Bongane
Expert 2120 points
Part Number: TPS65218

We have designed PMIC based custom board

PMIC output  becomes zero suddenly and now it output of DCDC4 reach to 2V and suddenly become zero within us  

As long as PB button pressed output of PMIC toggles and none of the output reaches to the desired level 

pls. suggest possible causes  

  • 0
    TI__Mastermind 30280 points
    Santosh,

    Can you please tell us the names of the Pins that are shown in the scope shot (Channel 1 = ?, Channel 2 = ?, Channel 3 = PB?)?

    It looks like there is a strong load on Channel 1 on the scope that causes a fault condition, so the rest of the PMIC rails sequence-down due to the fault. The expert on the TPS65218 should be able to suggest a better explanation of what is happening internal to the PMIC device.

    Do you have any additional files you can share with us, for example the System Block Diagram/Schematic/Board files?
  • 0 in reply to Brian Berner
    Expert 2120 points

    Hi,  Thank you

    We have been using the same board for testing and development since the may month 2017.

    Suddenly PMIC output voltages failed and facing difficulties to find out the cause of failure

    We have 4 more Custom boards and works fine.

    I have captured the new waveforms pls. find attached image. Block Diagram is almost similar to AM437x EVM kit except for NAND device.

    waveforms 

    PMIC circuit-

  • 0 in reply to Santosh Bongane
    TI__Expert 4155 points
    Santosh,

    I checked your schematic and I don't see any issues.

    Would you be able to place a shottky diode or a 100pF-300pF capacitor from ground to the L4A pin?

    Also, how many vias do you have connected to the powerpad?

    Are the output caps on the same side of the board as the PMIC, located close to the output pins?

    Thanks,
    Nick
  • 0 in reply to Nick Jakse49
    Expert 2120 points

    Hi,

    The same board was working before 2 weeks, now when we power on it by PB press 

    The input 5V drops and because of PMIC output toggles high to low ...&  low to high

    Input 5v to PMIC drops after PB press and in turns PMIC output drops 

    Does it mean that PMIC device malfunctioned?

  • 0 in reply to Santosh Bongane
    TI__Expert 4155 points
    Santosh,

    From the waveforms you captured it looks like BUCK4 is being shorted to ground.

    I think it is more likely that something else on the board went bad and is causing a short. Here is my suggestion.
    1. Probe the BUCK4 output to see if it is shorted to ground.
    2. If it is shorted check the output capacitor. If the capacitor is bad it will appear as a short.
    3. If it is not shorted place a shottky diode or a 100pF-300pF capacitor from ground to the L4A pin.

    Thank you,
    Nick
  • 0 in reply to Nick Jakse49
    Expert 2120 points
    Hi
    i did all the above three suggested pts
    But the problem still presist
    My query is not yet resolved.

    One key update

    When PMIC Output DCDC4 voltage toggle between high and low level at the same time input 5V drops below 4 volt and again rise to 5V

    I guess it's because of loading of PMIC output.

    How i can test the loading (overload) of PMIC?

    Or any other suggestion
  • 0 in reply to Santosh Bongane
    TI__Expert 4155 points
    Santosh,

    Just to make sure, if you used the schottky diode did you connect the cathode to the L4A pin? I realized I didn't specify that before. This part # is a good option for this: B230A-13-F

    If you want to test whether the output is being overloaded there are 2 ways I can think of measuring that. Unfortunately there isn't an easy way to test this by reading registers.

    1. If you have an oscilloscope current probe, cut the trace from DCDC4 to the load, and add a wire connecting them. Measure the current through the wire.
    2. Cut the trace from DCDC4 to the load and add a small resistor connecting them. Measure the voltage across the resistor to find the current through it. Keep in mind that the smaller the resistor the better as it will have less of an effect on the load, but also that if the load current is high the resistor will need to have a pretty high power rating.

    Also, you can try adding some more capacitance to the input to see if that will fix the drop in the input voltage.

    Thank you,
    Nick
  • 0 in reply to Nick Jakse49
    Expert 2120 points
    Hi

    But the same board works before 2 weeks back without any diode or capacitor.

    suddenly it stopped working and now as per suggestion i have connected capacitor it started again
  • 0 in reply to Santosh Bongane
    TI__Expert 4155 points
    Santosh,

    I am glad to hear that you got this working. I believe what you were seeing is a large in-rush current on DCDC4 that can happen due to bad grounding/ large output capacitance. The capacitor on the switching pin should fix it. Our next silicon revision, which is coming out early next year also fixes this.

    Thank you,
    Nick