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TPS7A4101: Input voltage to 5V

Dinglin You
Prodigy 140 points
Part Number: TPS7A4101

Dear experts,

Could I ask what will happend on the Vout if the Vin equal to 5V for the TPS7A4101 with feedback resistor 480K (To Vout) and 20Kohm (to GND)?

Thanks!

Dylan

  • 0
    Prodigy 140 points

    Hi Experts,

    I have checked the DS, and it shows the recommendated Vin min is 7V. Could I double-confirm with you if I have Vin 5V and nominal Vout equal to 27V, then the Vout will be 5V minus dropout voltage, am I right?

    Thanks!

    Dylan

  • 0
    TI__Genius 12511 points

    Hi Dylan,

    With an Rbottom of 20k and an Rtop of 480K, you are setting the output to 29.325V

    Vout ~ Vref(1+Rtop/Rbot)

    29.325V = 1.173V (1 + 480K/20K)

    This means that if your VIN is 5V, you will be pushing the device into dropout, losing the PSRR, noise and transient performance of the LDO.

    However, as you noted, VIN min is 7V, This means that you cannot expect full datasheet performance. I tested a similar device and the device functioned down to below 4V, so with a 5V input it should still work in dropout operation.

    Regards,

    John

  • 0 in reply to John Schneider
    Prodigy 140 points

    Hi Jonathan,

    Really appreciated for your strong support! Could I check with you what will be the output voltage if I have Vin 5V and setting the output to 4V via the feedback resistor Rtop and Rbottom？

    Thanks!

    Dylan

  • 0 in reply to Dinglin You
    TI__Genius 12511 points

    Hi Dylan,

    Dropout is heavily dependent upon temperature and load current for this device. However, at 25C even at full load, the device should regulate to 4V.

    In the worst case, VOUT in dropout would be at 3.7V.

    Regards,

    John