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TINA/Spice/LM5122: LM5122 After UVLO set to 0V, Vout remains at 12V.

Prodigy 40 points

Replies: 2

Views: 317

Part Number: LM5122

Tool/software: TINA-TI or Spice Models

Dear all,

I am working on a boost circuit to provide an output that behaves as follow:

Vin = 4.5V - 12V --> Vout = 12V

Vin > 12V --> Vout = Vin

I need to shut down the device and I tried to do this pulling the UVLO signal to 0V in a TINA simulation. What happens is that Vout remains at 12V and current continues to flow in the load (in the schematic it is a constant power load, but I also tried with a simple resistor). I cannot understand why this happens. How can I deactivate the HMOS? Wouldn't it be automatically done when UVLO=0V? Or am I misunderstanding the use of the LM5122?

(I took inspiration from TIDA-00699)

In this simulation the Vin remains stable at 12V. At 5ms I switch ON T1 so that UVLO voltage drops to 0V.

Has anybody suggestions?

Thank you very much,

Leo

  • Hi Leonardo,

    Please monitor the voltage between the high-side MOSFET gate and source. You will see that the high-side MOSFET is off, note that the body diode of the MOSFET will conduct and the output voltage will be the same as the input voltage, even when UVLO pin is pulled low.

    Thanks,

    Garrett Roecker
  • In reply to Garrett Roecker:

    Hallo Garret,

    Thank you very much for your answer, that's actually what I was thinking too!

    Regards
    Leonardo

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