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TPS74901: Dropout

Part Number: TPS74901

Hi expert,

Our customer want to use TPS74901.

Their application is below,

VIN: 1.1V

VOUT: 0.9V

IOUT: 0-2A

VBIAS: 5V+/-5%

VOUT RIPPLE:  6mVp-p

Their dropout is 1.1-0.9=0.2V. 

But our spec is max 280mV @ 3A.

And I didn't find max spec @2A. Below is just typ value.

So could you help to confirm can customer use in such application?

Thanks

Best Regards

Sean Song

  • Hi Sean,

    We will get back to you on Monday.

    Mark

  • Hi Mark,

    Thank you.

    I discuss with customer. The input of the device is a DCDC converter.

    Customer said they can consider to change Vin from 1.1V to 1.2V, but should they consider 1.2VDCDC accuracy, ripple and dynamic?

    If yes, for dynamic the output is 1.2+-5%, for accuracy and ripple the output is 1.2+-3%.

    So for 0.28V dropout, they should keep input voltage as 1.25V.

    But the max loss is too big, max input 1.2*105%

    1.2*1.05-0.9*0.995=0.417V

    0.417V*2A=0.834W

    It is big for them.

    Could you give your advise on the applicaiton?

    Thanks

    Best Regards

    Sean Song

  • Hi Sean,

    At a 1.1 Vin, 5 V bias, and 2A Iout, I am getting 0.87 Vout. At 1.74 A Iout I am getting exactly .9 Vout. I am using feedback resistors, of R1 619 ohms, R2 4.99 k Ohms.

    Hope this helps. 

    Thank you,

    Josh Nachassi

  • Hi Josh,

    Got it.

    Thank you very much.

    I will advise customer use as,

    VIN: 1.2V

    VOUT: 0.9V

    IOUT: 0-2A

    VBIAS: 5V+/-5%

    VOUT RIPPLE:  6mVp-p

    Should I consider 1.2VDCDC accuracy, ripple and dynamic?

    Thanks

    Best Regards

    Sean Song

  • At Vin 1.2 , Iout 2A, and Vbias 5V, I am getting Vout 970 mV and with only editing Iout I couldn't bring that value down unless you raise it past 2 A. I would recommend a 1.1 Vin to the customer, a 1.74 Iout with 5V bias to get a .9 Vout. 

  • Hi Josh,

    I am sorry about I am confuse with your new reply below.

    Your first reply,

    At a 1.1 Vin, 5 V bias, and 2A Iout, I am getting 0.87 Vout. At 1.74 A Iout I am getting exactly .9 Vout. I am using feedback resistors, of R1 619 ohms, R2 4.99 k Ohms.

    I think it may,

    1.1Vin , 5V bias, 2A Iout Vout=0.87V, and we set the Vout = 0.9V.

    It can't output 0.9V I think because 1.1V-0.9V=0.2V<0.28V @ 2A.

    1.1Vin , 5V bias, 1.74A Iout Vout=0.9V, and we set the Vout = 0.9V.

    It can output 0.9V I think because Iout decrease, dropout will lower when Iout lower

    Your new reply,

    At Vin 1.2 , Iout 2A, and Vbias 5V, I am getting Vout 970 mV and with only editing Iout I couldn't bring that value down unless you raise it past 2 A. I would recommend a 1.1 Vin to the customer, a 1.74 Iout with 5V bias to get a .9 Vout. 

    1.2Vin , Iout 2A, Vbias 5V then Vout=0.97V, and we set the Vout=0.9V

    I am confuse about why it happen.

    Would you please see if there is any clerical error in the reply?

    And customer can increase their input voltage, but they can't decrease Iout.

    So they need Vout=0.9V, Vbias= 5V, Iout=2A . and they can increase Vin from 1.1V to 1.2V.

    Thanks

    Best Regards

    Sean Song

  • Hi Sean, 

    I was able to get Vout to .9V at  Vin 1.2V and Iout 2A for my test. The max Vdropout from my test was about 80 mV. Let me know if you have any other questions.

    Thank you,

    Josh Nachassi

  • Hi Josh,

    How do you measure the Vdropout 80mV?

    I think it is,

    1 Set Vout 0.9V

    2 Set Vin 1V, Vout =0.9V

    3 Set Vin 0.98V, Vout =0.9V

    4 Set Vin 0.97V, Vout =0.89V

    So the dropout is 80mV

    Am I right? 

    Customer want use Vin=1.15V Vout=0.9V, Vbias= 5V, Iout=2A . If the dropout is 80mV, can customer use like this?

    Thanks

    Best Regards

    Sean Song

  • According to my test, that should work. I measured the dropout by decreasing Vin and measuring at what voltage does the output start to drop. Once I did that I subtracted Vin -Vout.