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TPS40200 50 VDC Input

David Robinson
Intellectual 855 points
Other Parts Discussed in Thread: TPS40200, LMV7271, TL7702A

TPS40200 typically turns on when input voltage is ~4.6 VDC. We need to keep the device off unitl the voltage reaches an input voltage of ~+30 VDC. Any ideas on how to do this. This will be a high temperature application. 

 

  • 0
    Mastermind 7395 points

    Use a comparator with open drain output. Connect the output of the comparator in parallel with the SS capacitor.

  • 0 in reply to Avi Chami1
    Intellectual 855 points

    The input voltage of 50 VDC goes to the DC/DC converter. The DC/DC converter is the only voltage conversion circuit available and we do not want it to turn on until we reach 30 VDC. What voltage do I use to power up the comparator?

     

  • 0 in reply to David Robinson
    Mastermind 7395 points

    You can use a comparator that can work with very low Vcc, like the LMV7271. To provide it with voltage, you use a low voltage Zener, could be even 2.1V, connected thru a resistor to the 50V (don't forget to put also a small capacitor). You add a reference voltage from the same Zener and a voltage divider, and another voltage divider for Vin that will be bigger than Vref only when Vin > 30V.

    For the Zener, let's say that we want 0.5mA when Vin reaches 4V. The resistance to Vin would be 4K. When Vin = 50V, the current thru the Zener would be 12.5mA. A Zener like MMSZ4679T1G could make this.

    Alternatively, you can check voltage supervisory devices. Their advantage is that they already include an internal reference and usually they activate their output for Vcc as low as 1V. You will still may need to make a Zener regulated voltage supply, since I don't know supervisory devices that can wthstand Vcc of 50V. For example, check the TL7702A.

    Hope this helps.