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TPS7B4253-Q1: Dropout Voltage

Shota Mago
Expert 8170 points
Part Number: TPS7B4253-Q1


Hi team,

I'm an FAE supporting some industrial company in Japan.

Could you please provide dropout voltage at following condition?

  • Input Voltage: 28~35V
  • Vadj: 2.5V
  • Output Voltage: 27V
  • Load current: 100mA

Although Fig.4 and Fig.5 shows Vdrop, it's the case of Vin=Vadj=4V.

In addition, though 6.5 shows max Vdropout=520mV, it's the case of Vin=Vadj>4V.

I'm looking forward to hearing from you.

Best regards,

Shota Mago

  • 0
    TI__Guru 55940 points

    Hi Shota,

    The test conditions of Vin = Vadj are used in order to force dropout.  TPS7B4253-Q1 operates in unity gain as shown in the functional block diagram, so in order to force the device into dropout in order to measure the voltage drop between Vin and Vout (dropout), Vin is set to Vadj.

    As Figure 4 shows, dropout is linear on TPS7B4253-Q1 with respect to current; therefore, we can calculate the maximum dropout at 100 mA by setting up a ratio:

    Vdomax100 / 100 mA = Vdomax / 200 mA

    Vdomax100 = (520 mV / 200 mA) * 100 mA

    Vdomax100 = 260 mV

    With our calculated maximum dropout you can see that your minimum headroom of 1 V is plenty to keep the output within regulation.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    TI__Expert 8170 points
    Hi Ryan-san,

    Thanks for your detail answer.
    Just for making sure, when output current is 100mA, the dropout voltage will be 260mV regardless of input voltage.
    Because dropout voltage is 260mV at unity gain.

    Is this my understanding correct?

    Best regards,
    Shota Mago
  • 0 in reply to Shota Mago
    TI__Guru 55940 points
    Hi Mago-san,

    Dropout is a measure of how much headroom (Vin - Vout) is required to maintain a regulated output. As such with a 100 mA load, your input voltage must be 260 mV higher than your output voltage in order to maintain regulation.

    In your application your input voltage is 1 V higher than your output voltage at the lowest Vin. As such your application should maintain regulation.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    TI__Expert 8170 points
    Ryan-san,

    I got it .
    Thanks a lot!

    Best regards,
    Shota Mao