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TPS54232: Input current consumption becomes higher when changing diode

Cindy Chang
Intellectual 2475 points
Part Number: TPS54232

Hi,

We want to know that is it correct that input current consumption be 30mA more when we change D25 from ES1G_YJ to FR1G?

If yes, why?

If not, what may cause this problem?

Thank you.

FR1G.pdfES1G_YJ(1).pdf

Best Regards,

Cindy

  • 0
    TI__Prodigy 400 points

    Hi Cindy,

    This makes sense to me. I believe that the increased current you're seeing is due to the different reverse recovery times of the two diodes. The ES1G has a maximum specified reverse recovery time of 35 ns, while the FR1G has a maximum reverse recovery time of 150 ns.

    The duty ratio can be approximated as D = Vout/Vin = 3.3/15 = 0.22. For a switching frequency of 1 MHz, each period is T= 1/fsw = 1 us. So, the diode should be expected to be blocking for approximately 0.22*1 us = 220 ns per period, and conducting for approximately 780 ns per period.

    As you can see, the 150 ns reverse recovery time makes up a significant portion of the time that the diode should be blocking. If you can obtain SPICE models, I recommend simulating this to confirm if this is the case or not. Even better would be if you are able to measure the diode current on an oscilloscope to verify if this is indeed what is occurring.

  • 0 in reply to Kevin Bradford
    TI__Prodigy 400 points

    Hi Cindy,

    I just realized that the images didn't post. Please see attached.

  • 0
    TI__Expert 4795 points

    Hi Cindy,

    What't the loading current conditon when you say input current consumption is 30mA higher? Different diode has different VF so it is reasonable to change the efficiency/input current a little bit.

  • 0
    TI__Guru 54140 points

     

    Looking through the two datasheets that you shared, the only significant difference between the devices appears to be the reported reverse recovery time of 35ns for the ES1G and <150ns for the FR1G, as Kevin Bradford pointed out.  The additional reverse recovery time of the FR1G could result in the increased input current.

    Is there a specific reason for using 400V reverse rated diode with a 28V rated switcher?

    These diodes have higher capacitance, forward voltage drop, and reverse recovery time than lower-voltage 1A diodes, which would provide higher efficiency, and likely lower cost, than either the FR1G or ES1G can offer.  For example the SS14-LTP is a 40V 1A schottky barrier diode.  It has a forward drop of 500mV @ 1A compared to 1.3V on both the FR1G and ES1G and a junction capacitance of 52pF and is the same DO-214AC package.

    https://www.mccsemi.com/pdf/Products/SS12E-SS110E(SMAE).PDF

  • 0
    TI__Prodigy 400 points

    Hi Cindy,

    Any updates on this? We'd like to close this thread out if your issue has been resolved. Thanks!