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LTC3114 Damage failure for Vout > 20 V

Hi all,

I'm designing an application where the LC 3114 is used in boost mode (from 15 V to 18/32 V).

I have captured oscilogram for 18 V:

... and for 25V output:

Yellow probe - LTC3114 output

Green probe - current to LTC3114 input (from llaboratory power supply) 

When I set output to 32 V,  the device have failed. I think thath internal transistor is punctured by current peaks (level depends on output voltage).

L = 22 uH

Cout, total = 22 uF / 62 uF (i keep the dc bias effect in the mind) 

EVAL board used schottky diodes on ouput and SW1, it there any effect of these diode on my damage problem?

https://www.analog.com/media/en/technical-documentation/u, it there any offect ot these diode oser-guides/scp-ltc3114-1-evalz.pdf

Thanks in advance!

Tomas

  • Hi Tomas,

    For high output voltage (boost mode), suggest that to unstuffed Schottky diode (D1). The configuration with the Schottky diode from the output to LDO is recommended for ONLY 5V output application for better efficiency. As indicated below. The abs max of LDO (pin 9) was maximum rated at +6V.

    Also, be mindful of capacitor voltage rating (e.g. 50V cap rating) used on this evaluation board.  

     Regards,

    Xian

  • Hi Xian,
    Thank you for your response.
    I do tests without Schottky diodes D1 and D2 but setting the required output voltage 32 V damages the LTC3114 circuit.
    Could it be caused by missing the D2 diode in the circuit?
  • Hello Tomas,

    Kindly provide an updated schematic diagram. Also, list down all the component you changed and please include part number/specs especially to the inductor (L =22uH, C=62uF, etc.). Could you also provide test condition/s on what you have done? Ex: What was your output current when you turned on the unit? Or did you turned on the unit without an output load?
    Could you also provide your email contact so we can communicate to you directly?

    Thanks in advance.

    Daniel

  • Hi Daniel,

    the original inductor was a SRR1260-220M (but I modified it to IHLP3232DZER4R7M01 4.7 uH), this change solved original problem (converter runs for both ouput levels when no load is conected). Because 18 V ouput level works fine for all test conditions I have continued only with 32 V ouput level. There are two scenarios:

    1) Converter is powered by laboratory power supply (with relative fast overcurrent protection). On Figure below there is a ramp of ouput voltage for this case:

    tescan-my.sharepoint.com/.../EZYoQnO4TylFuTvJgQd2P28BMXnmc3SjHlcVNiWqMT1uJA

    2) Converter is powered from the 15V line power source (no overcurrent protection) - this caused damage of converter (behavior of this failure is a) low ouput voltage (indipendently of FB voltage or b) internal overshoot to ground (resistance between SW1/2 and GND  goes to zero).

    My company email is tomas.svoboda2@tescan.com, I am able to provide schematic (with parts number of used components),

    Thanks,

    Tomas

  • Hi Tomas,

    I would be interested in if you solved the problem in meantime.

    If yes, could you please let me know?

  • Hi huni,

    Yes I solved it - the problem was probobly too large inductor (prototype with a smaller inductor works fine), final board is delayed (missing others components) but this issue can be marked as resolved.

    Thanks,

    Tomas