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TPS7A4001: Usage as current source

Part Number: TPS7A4001

Hello team,

Can the TPS7A4001 be used as a constant current source similar to other LDOs? and if so is this the correct way of doing it?

Thanks in advance.

  • Hi Panagiotis,

    We often see this type of thing when applications are looking to drive LEDs and TPS7A40 is a great candidate for doing this type of thing because you can use a larger number of LED's in series due to the LDO's 100V capabilities. 

    Your example diagram is the most common way to do this since the LDO regulates the FB node to be equal to the internal reference. This means that you will always have a load of Vref/120. 

    You could also consider putting your constant load between the input source and the LDO input pin. Below are some reasons why you may want to consider this method, it was originally tailored for LEDs (as you can see in the block diagram) but it may be applicable to your load as well.  

    • When disabled the LDO will turn off the current hard resulting in a more predictable behavior
      • When on the output charge held on the output cap will continue to drain until the forward bias is no longer enough to light the LED
    • When enabled the current through the LDO should be enough to turn on the LEDs immediately
      • when the LEDs are on the output, Cout must charge up to the forward voltage before the LEDs will turn on
        • maximum PWM frequency is determined by the LDO enable circuitry and not the inherent RC delay of the output
      • The input and output caps should be matched (or the input cap larger) to allow the initial charging current for Cout to come from Cin thus limiting excess current draw through the LEDs.

  • Thank you very much Kyle for the info, this is very useful for this and future projects

    Cheers,

    Panagiotis