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TPS7A49: VOUT less than 1V of Vin

Part Number: TPS7A49


The datasheet recommends that VIN ≥ VOUT(nom) + 1 V.   However, under normal operation in section 8.4.1 it lists one of the modes as:  The input voltage is greater than the nominal output voltage added to the dropout voltage.

What is the reason for the 1V headroom and if that is necessary why is there even a drop out value listed that is less than 1V?

I want to use this part in an application where there is 11.5V Vin and 11V VOUT with 20mA current.  I appears that would be ok based upon figure 9.  Yes?

  • Hi Alan, 

    Vdo is often referred to as the minimum voltage difference between Vin and Vout needed for the LDO to regulate. 

    The datasheet recommends that VIN ≥ VOUT(nom) + 1 V.

    Are you referring to the conditions listed above the EC table and each section? 

    If so, this is the condition used when testing the device, unless otherwise specified. This is very common and almost a standard. 

    There are other things to take into account, i.e how well your input is regulated, Line Regulation, Accuracy, Transients that will help determine how much headroom you need. 

    For your application, from figure 9, worst case would be a Vdo~175mV. With 500mV of given headroom, you still have some room. 


    Edgar Acosta