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LM53603-Q1: LM53603 input voltage requirement

Kevin Van Arendonk
Prodigy 50 points
Part Number: LM53603-Q1

I am using the LM53603-Q1 voltage regulator chip with a fixed output voltage of 3.3V and 2.2A max output current.  The part works great with an input voltage of 25V but I need it to work down to about 4.5V.  The datasheet says it should work with an input voltage down to 3.5V.  Also Webench gives an error when trying to simulate with a 4.5V input voltage.  Can anybody explain the discrepancy between the datasheet and Webench?

Thanks,

Kevin

  • 0
    TI__Guru**** 191445 points

    The actual vin drop out voltage will depend on the output current , but it should certainly support 3.3 V output with 4 V input.  This is most likely either a Webench error.  I will move this to the Webench forum so they can investigate it.

  • 0 in reply to JohnTucker
    Prodigy 50 points

    Thanks for the quick reply.  I should have mentioned earlier when I apply 4.6V to the input of the regulator (on real hardware, not Webench) the output voltage is only 1.88V.  So Webench seems to agree with the real world, unless they both have an error.

    Thanks,

    Kevin

  • 0 in reply to Kevin Van Arendonk
    Prodigy 50 points
    With the help of an FAE, I figured out this problem. According to the datasheet, this part is not able to work at lower input voltages and higher output currents. Figure 14 on page 17 of the datasheet explains this relationship.

    Thanks,
    Kevin
  • 0 in reply to Kevin Van Arendonk
    TI__Guru**** 191445 points

    Yes figure 14 shows the behavior I was alluding to, that the drop out voltage is dependent on output current.  If you look at the slopes of those curves during the drop out region, you will find that (Vin - Vout) / Iout approximately equals the RDSon of the high side FET.  Notice also that those curves are for 5 V output.  They do not explain why you would only get 1.88 V output with 4.6 V input.  You may want to look into this further.