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TPS62110 hysteresis

TPH01
Prodigy 70 points
Other Parts Discussed in Thread: TPS62110, TPS62125

Hi,

I'm using a TPS62110 as a +15V to +7.5V converter (component values bellow). I was checking the load regulation by connecting different valued power resistors to the regulator's output when I noticed hysteresis in the output voltage. I used a minimum load resistance of 22R (340mA). Then (leaving the regulator running) I connected an additional 10R load resistor to increase the load current by 0.75A. I noticed that when I disconnected the 10R load resistor, the regulator's output did not always return to its original value. On repeated connection + disconnection cycles, the output would settle down to values differing by 10s of mV. 

Any idea what's causing this?

Best,

Tom

The inductor is a Coil Craft XAL6060-223ME 22uH, 5.6A Isat 

Cout is 2x22uF 25V ceramic

Cin 2x22uF 25V ceramic

Cff is 22pf

Feedback divider is 560k + 100k

  • 0
    TI__Genius 16025 points

    Hi TPH01,

    Thank you for your question. I will direct your post to the appropriate forum.

    Thanks,

    Anston

  • 0 in reply to Chris Glaser
    Prodigy 70 points
    Chris,

    Thank you for the answer -- although it would have saved me a lot of time if there had been some mention of that in the datasheet!

    Is there anything else you can tell me about this behaviour? e.g. what size transient triggers it? How big is the largest step size? Or, do I just have to assume that the output voltage could change by the regulator's entire +-3% tolerance at any point?

    The context here is that I want to power some relatively low noise analog circuitry from the switch mode regulator. I can filter off the switching noise easily to get to something acceptable, but a max step of 6% in the DC supply voltage would cause problems.

    Tom
  • 0 in reply to TPH01
    TI__Guru**** 150950 points
    Yes, the device will be within 3%, but you can't guarantee where it will be in that range.

    The ripple/noise should be the same with any voltage. It's just the DC setpoint that's different.

    Do you really need that much current for a sensitive analog circuit? If not, there's the TPS62125 which does not show this behavior.
  • 0 in reply to Chris Glaser
    Prodigy 70 points
    Okay, thanks for the info.

    We need a fair amount of current because it's a multichannel system of ADCs + DACs + in/out buffers. We also already have several TPS62110s to power the digital section of the board, which does need up to an amp, so it's simplest to use the same reg everywhere.

    I'll have a think about what's best for us.

    I really do think it would be worth adding this to the datasheet though....

    Tom