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TPS2557DRBEVM-423: TPS2557DRBR

POORTI VARSHNEY
Prodigy 60 points
Part Number: TPS2557DRBEVM-423

Tool/software:

Hello,

I keep the current limit as 4A and keep the  Rlim as 27.7 kohm and Iam giving the input voltage as 2.8V but it is dropping by 1-1.5V when I am keeping the load of 3.7A . Can you please let me know what is the reason behind the same.

Thanks

Poorti

  • 0
    TI__Prodigy 590 points

    Hi Poorti,

    Equation 1 in section 10.2.1.2.2 (https://www.ti.com/lit/ds/symlink/tps2556.pdf) approximates the resulting overcurrent threshold for a given external resistor value (RILIM).

    With a 27.7 kOhm resistance, the Ios_min is around 3652 mA, which is lower than the 3.7 A test condition as you mentioned. You may change the resistance according to the equations above. Ios_max/nom/min could give you a rough idea of the current threshold range with selected resistors. Additionally, 1% resistors are suggested to ensure the resistance accuracy.

    BR,

    Ke Wang

  • 0 in reply to Ke Wang
    Prodigy 60 points

    Hello,

    I noted your your suggestion but I found that the voltage was dropping even at the 100 & 200 mA which is insignificant.

    I hereby attached the picture of load characteristics of teh same., KIndly check

    Thanks 

    Poorti Varshney

  • 0 in reply to POORTI VARSHNEY
    TI__Prodigy 590 points

    Hi Poorti,

    I noticed than from 400 mA load and above, the current drop almost follows 0.54 V/A. Since the Rdson of the switch of TPS255x is 22 mOhm in datasheet, could you check:

    1. Whether the power source you are using is strong enough? Can you check the output impedance of it?

    2. Can you find a 0.5 Ohm resistance in the power loop before output? Measuring the Vin and Vout directly on the IC pins may help to locate it.

    BR,

    Ke Wang