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behavior of LM5116 in case of Vin<Vout

Simon Nussbaumer
Prodigy 60 points
Other Parts Discussed in Thread: LM5116

Hallo

I'm considering to use the LM5116 in my design. The specs for normal operation are:

Vin: 60..75V

Vout: 12 V

How ever, I wonder how the LM5116 works for Vin < Voff,nom (=12 V). (only appears in fault cases)

My assumtion is that the LM5116 operates at max duty cycle, which is a limited by the switching frequency and the minimum off time. 

Is it possible to clamp the Vout to Vin for that case by using the UVLO and a Pull-up resistor for the high switch?

(The aim is to keep Vout as high as possible if Vout<12V)

Thank you for your help!

Simon

  • 0
    TI__Guru 58761 points

    Hi

    If the output voltage is less than your input supply voltage, there will be an unlimited current flow through the high-side MOSFET body diode. Eventually the MOSFET will be damaged.

    If the output impedance of the power supply which is supplying 12V at Vout is high enough to limit the current flows through the high-side body diode, the output voltage will be limited to' Vin + forward diode drop of the high-side MOSFET(0.7~1.0V)'

    Regards,