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LMZM23601: -12V Inverting Application having issues

Part Number: LMZM23601

We've designed 3 different inverting circuits based on your online Webbench simulator using the LMZM23601 part at -5V, -9V, & -12V.  We're seeing failures only with the -12V application and we've noticed a discrepancy between the app note SNVA807A and the online Webbench simulator.  C_byp is noted in the app note to be a minimum of 10uF capacitance where the Webbench simulator recommends a 0.1uF capacitor.  Which is correct and could this be causing this part to fail?

  • Hello Adam,

    Sorry to hear of the difficulties. Can you share the schematic in its entirety and any waveforms you have available?

    I would err closer to 10uF. I don't believe this to be hard number, though. 100nF seems a little low, especially considering DC bias derating.

  • System Power = 9V - 24V

    -VA_AOUT = -12V

    +VA_PS_AOUT = +12V

  • Hello Adam,

    I would increase bypass to 10uF.

    In addition, if not done already, I would recommend confirming:

    1. Does output voltage come-up upon Vin application (With no load)?

    2. If it does, confirm  what is the max loading you can obtain out of the device.

    3. "System Loop Stability" section in SNVA807 notes the stability analysis for the converter. A 22uF + 47uF capacitor was used. (47uF=16VDC, 1206 and 22uF=50VDC, 1210). If you are unable to get the regulator to startup, I would consider adding 2 additional pieces of the 10uF, 50VDC capacitor you are using.

  • Hi Marshall,

    This supply has come up without issue, what's been happening on a few boards is it ends up shorting internally to the IC itself which then prevent the circuit from operating.  Didn't know if that C_BYP cap would have anything to do with that or we're thinking more and more that it might be a manufacturing issue.

    We have 3x of these inverting circuits and we modified another one to operate at -12V (was operating without issue at -9V) and we have been running it for a week or so without seeing these same issues.

    Thanks for looking into this for us.

  • Hello Adam,

    That is good to hear. Best of luck with the rest of your design.