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LM5008: Disableing the chip using a shotky diode.

Ahmad Farjami
Prodigy 20 points
Part Number: LM5008

Hello, dear support team,

I need your help in using LM5008 to regulate input voltage 20V to 90V into 15V. 

To have power up/down sequencing, considering that I do not want to use any transistor in this circuit, I am planning to disable the chip using a schottky diode connected to the power good of another regulator, as shown below.

My concern here is reverse current of that schottky diode when the PG high level voltage is 5V and as stated in the datasheet RT/SD pin is 1.5V to 3V. In case we have high temperature and the diode reverse current goes high, for example to 1mA, what will happen?

I am not sure how much current will go to RT/SD pin and where should this current go, it may reduce the current passing through R547, but probably will affect the switching on time and frequency as well.

Many thanks,

Ahmad

  • +1
    TI__Guru 73010 points

    Hi Ahmad,

    Thank you for considering our product. I think you concern about the frequency is valid. Like recommended in the datasheet, I would strongly recommend to use a small NFET controlling by your PG_+5V. Such a small signal NFET would not cost much more than a Schottky diode.  

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 20 points

    Hi Youhao,

    Thanks for the reply. The problem is not the price but a new PN to the BOM beside the space scarcity.

    Then, as you mentioned, I would try to use NFET or something similar to switch the pin to ground.

    Best regards,

    Ahmad