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Original question:

TPSM82821: max output capacitance

TPSM82821: Quiescent current

user3775977
Prodigy 40 points
Part Number: TPSM82821

Unfortunately we are facing severe problems with the TPSM82821 (LiPo to 3.3V) voltage regulator one of our boards - a detailed summary is attached.

1. The regulator shows a dramatically increased current draw, at capacitive loads, that are within the datasheet limits. 
When loaded with a nominal (derated) output capactiance of 40-45µF, the regulator will draw short high current spikes (>=30mA) without any load. This increases the average quiescent current dramatically. 
The output seems to be stable in this condition, while the input current consumption increases.

2. The regulator shows an increased current consumption in low-dropout mode.
While the datasheet states 10µA maximum quiescent current, the quiescent current increase to the 100µA+ range.

The behaviour of (1) and (2) seem to be independent of each other and both effects seem to very between device and device (but with a sample size of 2, this is really no metric at the moment).

TPSM828214SILR-issue-report.pdf

  • 0
    TI__Intellectual 1310 points

    Hi,

    Thank you for reaching out.

    I will need some time to look at this in more detail.

    I'll get back to you early next week at the latest, if that is okay with you.

    Best regards,
    Louis

  • 0 in reply to Louis Colbach
    TI__Intellectual 1310 points

    Hi,

    Apologies for the delayed response.

    1. Does this issue happen with both devices?

      The report says everything at the load was in deep sleep.
      Ideally, I would like to know if the issue still occurs in a fully controlled environment, i.e. when there is actually physically no load and the input is a bench supply. Or, if you for example have the TPSM82821EVM, if the issue also happens on that board.

    2. I checked internally, the measured increased quiescent current you see in dropout mode is normal behavior.
      The provided 10uA Iq in the datasheet is for a standard buck VIN-VOUT relationship. 100% duty cycle mode is considered a feature, not standard operation.

      How important is 100% duty cycle mode for your application?

    Best regards,
    Louis

  • 0 in reply to Louis Colbach
    Prodigy 40 points

    Hi Louis,

    1. Yes, this happens on both devices (we have 300 prototypes ready, so I can test with more).
         I didn't try to isolate the issue, but I guess I can just stack up addtional capacitance and resistance on the output until it gets unstable. 
         I don't think, that there is an EVM for the TPSM828214A (fixed 3.3V) and I can imagine, that this makes the difference due to the internal resistor divider and feedforward capacitor, that compromise the loop stability. 

    2. Understood
        As this is an intended operating mode for this device, please qualify it accordingly and add the current consumption in dropout mode to the device specification. As it is now, this is clearly misleading/false, as the Iq is clearly marked for "EN = High, no load, device not switching" - all conditions apply in dropout mode. 
        Technically I understand, that you are probably using the primary NMOS to accomplish the Low-Dropout mode, but it is unclear how much current the internal gatechargepump draws or if you potentially use a secondary PMOS path to achieve Low-Dropout operation.

    Kind regards 
    Bernhard

  • 0 in reply to user3775977
    TI__Intellectual 1310 points

    Hi Bernhard,

    Please try to isolate the module to check whether there's not something intermittently drawing this 30mA current at the load, even though the load is considered to be in "deep sleep".

    You are correct, there is no direct EVM for the fixed output voltage options, but you should be able to replace the TPSM8282x on the TPSM82821EVM-080 with a TPSM828214 from one of the prototype boards with the issue. Then, in the EVM schematic below, remove R2 and C3, short R1 and adjust the input/output BOM according to your use case.

    Regarding 2., I fully understand your concern. I will forward this internally.

    Best regards,
    Louis

  • 0 in reply to Louis Colbach
    Prodigy 40 points

    Hi Louis,

    When measuring the load, the current consumption is constant at around 80µA, but I understand, that this is not reproducable for you.  

    I'll try to isolate the issue further with our current prototypes. If I can do that easily, I'll buy an EVM and try to repllicate it there - but this may take. 

    2) Please do so. This cost our customer ~50k€ in prototypes and me a lot of headache

    Kind regards
    Bernhard