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Original question:

TPS74801: VBIAS dropout voltage

TPS74801: VIN dropout voltage

Xiwu Li
Prodigy 10 points
Part Number: TPS74801

Hi,

I have a problem with the dropout voltage of VIN.

The maximum value of VDO (VIN) in ”6.5 Electrical Characteristics” is 165mV,

but in Figure 6, the maximum value I can get under the same situation ( VBIAS-VOUT = 3.25V,Iout = 1.5A ) is only ~83mV.

I want to know how the maximum value of 165mV is obtained, why these two values have almost doubled, and how to confirm this maximum value in my design

My spec, VIN=2.5V, VBIAS= 5V, Vout= 1.8V, IOUTmax= 500mA

Best regards,

Xiwu

  • +1
    TI__Mastermind 38115 points

    Hi Xiwu,

    The data in the figures from the datasheet are typical values and the typical values in the EC table are at 25C. This is why the typical value for dropout in the EC table (60mV) agrees with the 25C curve from Figure 6 at VBIAS - VOUT = 3.25V. 

    The max specification in the EC table is 6σ or 6.6σ values from a larger sample size and includes the full temperature range. 

    Note that dropout voltage increases as load increases. So, the 165mV max specification at 1.5A load covers the worst-case operating conditions and for your application (i.e. load current < 1.5A) you would actually measure less than that. Unfortunately we do not have further data to share on this so if you use the 165mV max specification that would also include margin.

    Regards,

    Nick