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Original question:

TPS7A74: Power supply for BIAS pin

TPS7A74: TPS7A74

syed S
Prodigy 90 points
Part Number: TPS7A74

Tool/software:

Hi Team,

I am using the TPS7A7401DSDR part for Vin=1.8V & Vout=1V with Bias Voltage of 3.3V, Iload=1A

While checking for the drop out voltage, the condition fails for my case. so what would be the required drop out voltage for Vbias=3.3V

from the graph i could see the drop out voltage value for the Vbias=5V condition, i need to know whether i can use for my requirement.

the below graph shows the drop out voltage more than 750mv, which is not possible for my Vin, Vout range.

the graph values shows 750V in the Y-axis, is it a typing mistake?

  • 0
    TI__Prodigy 730 points

    Syed,

    Yes, the y-axis should be mV not V. Y axis should be from 0 to 1.25V. 

    From your listed conditions, I believe this should work. You have 0.8V of headroom on VIN which is above the worst case value of 180mV per the datasheet.  On Bias, you have 2.3V of headroom, which is also above the worst case of 1.3V from the datasheet EC specs and graphs. 

    Since VIN and VBIAS are powered from separate supplies in your application, the graphs you shared are the dropout requirements on the bias pin, not the vin pin. The actual dropout requirements for the vin pin can be seen from below graph. Just a reminder this is only true because Vin and Vbias are coming from separate supplies. If Vin and Vbias are tied together, then the graphs you shared would be the dropout requirement for both Vin and Vbias. 

    Best,
    Jaime

  • 0 in reply to Jaime Flores
    Prodigy 90 points

    Hi ,

    the graph you are referring is the Vin drop out voltage for Vbias=5V but in my case the Vbias=3.3V, how to know the Vin drop out voltage for Vbias=3.3V. how to calculate it?

  • 0 in reply to syed S
    TI__Prodigy 730 points

    Syed,

    Let me ask the team if we have any data on this.

    Best,

    Jaime

  • 0 in reply to syed S
    TI__Prodigy 730 points

    Syed, 

    our team is looking into this. Should have more info next week.

    Best,

    Jaime

  • 0 in reply to Jaime Flores
    TI__Prodigy 730 points

    Syed,

    Our team believe this should be fine based off of the datasheet graphs. 

    Best,

    Jaime