Cannot generate -5V from 6V with LT8362 and LT3091

Hello,

I have an issue with my power supply tree:

6V -> LT8362 -> -6V -> LT3091 -> -5V

When I power on my board and I enable the LT3091:

- the LT8362 output is oscillating (dc=-5.5V, ac=1.5V)
- the LT3091 output is noisy

Please find above my schematic

- the schematic works well with LTSpice
- the LT8362 works well and generates -6V when the LT3091 is disabled
- the LT3091 works well  when I supply the -6V with a lab power supply.

Any thoughts ? It would be very appreciated.

Thank you !

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  • 0
    •  Analog Employees 
    on Feb 18, 2021 11:55 PM

    Hi avasygn,

    I run simulations on your Inverting converter. Have you tried simulating using lighter load? I tried simulating from 750mA to 1.5A and it seems that it is stable at 850mA. The converter can reach at -6V, 1A but there is an increasing oscillation, which could possibly shut down your Inverting converter (Current limit).  

    At 1.5A, it cannot sustain -6V and drops around 4.5-5.5V, therefore you're reaching dropout stage. This is the reason why you are seeing noisy output at LDO.

    This simulation below runs at -6V, 7 Ohm load.

    Regards,

Reply
  • 0
    •  Analog Employees 
    on Feb 18, 2021 11:55 PM

    Hi avasygn,

    I run simulations on your Inverting converter. Have you tried simulating using lighter load? I tried simulating from 750mA to 1.5A and it seems that it is stable at 850mA. The converter can reach at -6V, 1A but there is an increasing oscillation, which could possibly shut down your Inverting converter (Current limit).  

    At 1.5A, it cannot sustain -6V and drops around 4.5-5.5V, therefore you're reaching dropout stage. This is the reason why you are seeing noisy output at LDO.

    This simulation below runs at -6V, 7 Ohm load.

    Regards,

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