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TPS74201 Vbias

Other Parts Discussed in Thread: TPS74201

My customers asks:

I interpret from the datasheet for the TPS74201, Vbias >=  Vout + 1.62.

 

So for 1.2 Vout you need Vbias >= 2.82V and for 1.0 Vout you need Vbias >= 2.62V. If Vbias is 2.5V then Vout should be 0.88V .

I am not 100% sure is that the requirement or that is just a test condition for their measurements.

 

The second row says Vbias = 2.375 (min) without any conditions…

 

I am investigating if this LDO can make the same output voltages (1.0 and 1.2) with 1.5V input and 2.5V bias voltage.

Can you please confirm?

  • The electrical characteristics table puts limits on many parameters, such as Vin, Vout, and load to name a few.  These limits are AND-ed.  The first limit, defining the Vbias range from 2.375 to 5.5, must be met AND a minimum Vbias to maintain a given Vout.  This minimum Vbias can be found from the graphs based on dropout--this is figures 9 and 10.

    The 1.62V frequently noted in the test conditions column is a test condition.  At this differential, the dropout and LDO performance will not be significantly limited or defined by the Vbias level and so the parameter in question can be measured independent of any Vbias effects.

    The Vbias range of 2.375 to 5.5V is the Vbias range over which the part has been characterized and is guaranteed to work, assuming the other limits are met.

    Now to your real question.  Figures 9 and 10 show that you have the needed dropout for each of your cases, assuming the load is no more than 1.5A.  For the 1.2V case, that is 1.3V of Vbias to Vout drop which yields a maximum dropout of around 120 mV at 125C.  This is less than the required dropout of 1.5V - 1.2V = 300 mV needed.