TPS2557: Output voltage drop

Part Number: TPS2557

If a large current is applied, the output voltage will drop.

When the current is small, there is no problem with output voltage = input voltage.
When the current flows up to the limit value max, the output voltage != Input voltage.

What is the cause of the difference between the output voltage and the input voltage?

Specifically, the input is 5.0V and the output is 3.7V.

When further current is applied, EN = Low and the output voltage becomes 0V.

Thank you.

  • 1. As without above current limit, the voltage drop is due to the Rdson of internal Mos.

    2. As above current limit, the voltage drop is due to the MOS which works in saturation region. You can regard the Mos internal resistor is much bigger as in OC condition.

    3. When EN=low, the power switch is disabled. Internal Mos is turned off.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • The ON resistance of the MosFET of this IC is only about 22mΩ.
    On the experimental board, the input voltage is 5V and the output voltage is 3.7V when the current is 3.8A. The current limit is set to a maximum of 4A.
    Even if a current of 3.8A flows, the voltage will drop by about 100mA at most.
    Does the ON resistance of MosFET change up to 340mΩ?
    What is OC condition?

    Thank you.

  • Measure the pin voltage by Kelvin method.

    The cable voltage drop and connector voltage drop influences.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • The voltage of the input terminal and output terminal of the IC is measured with an oscilloscope.

    Cable voltage drops and connector voltage drops are unthinkable.
    Is my question conveyed correctly?

    Thank you.

  • 1. Please confirm whether you measure the IC pin voltage instead of connector voltage.

    2. Please confirm IC is not in current limit condition. You can reduce the current and check whether the voltage change a lot.

    3. 4A* 200mohm=0.8V. For cable and connector, it's reasonable to be that value.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • 1. The measurement point is the IC pin.

    2. There is no current limit. nFAULT = HIGH.When the current is reduced, the voltage has returned to 5V.

    3. No cable used.

    Thank you.

  • 1. Where is the GND measure point you set?

    Please put the GND point also close to the IC pin.

    2. Please also get noted that the Rdson is also related to the temperature. Refer to figure10 of datasheet.

    3. If still any concern, please have a test on EVM.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • 1. GND point is TPS2557 -1pin

    2. I don't think there will be a voltage drop of 1V or more even if Figure 10 in the data sheet affects it.

    What is the cause of the output voltage dropping to 3.7V before nFAULT goes low?

    3. What is EVM?

    Yellow Line is the input voltage at TPS2557 -2pin

    Blue Line is the nFAULT  Status at TPS2557 -8pin

    Green Line is the output voltage at TPS2557 -6pin

    Another problem is that I set the current limit to 3390mA-4068mA, but in reality nFAULT goes LOW above 4068mA.

    Thenk you

  • Before fault asserts, it has 9ms deglitch time.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • What inquiry is 9ms deglitch time answered?

    I will reorganize my question.

    1.  Why does the output voltage drop to 3.7V?

    2.  The current limit is set to 3390mA-4068mA, but why isn't fault asserted unless 4068mA or more flow?

    Thenk you.

  • 1. 9ms deglitch please check datasheet page5.

    2. It has some tolerance such as the tolerance or resistor and so on.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • 1. Keeping the load at 4A will keep it at 3.7V. How does it relate to deglittch time13ms?

    2. The resistance value is 29.4Ω from the table on page 16 of the data sheet. Isn't it MIN3390mA or MAX4068mA considering the resistance tolerance?

    Thank you.

  • Please contact the FAE who support you and send me one email. I can have a check on bench.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • How do I get FAE support and contact?
    Does that mean E2E can't solve it?

    Thank you.

  • For some case need to be tested, we support it based on our bandwidth and procedure. If don't have one FAE support you, you can have a test on EVM first.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • Who should I contact?
    Please provide the URL or support contact information.

    thank you.

  • Can you have a test on EVM first? You can apply for the EVM on ti.com.

  • I'm sorry I don't understand. Why do you recommend purchasing an evaluation board?


    I am inquiring about the features of TPS2557.
    Ask again. Is there such a possibility? Please answer Yes or No.
    1. Is it possible that the output voltage will drop to 3.7V before the current limit occurs? The conditions at this time are Vin = 5.0V, current limit Max = 4068mA (RILIM = 29.4KΩ)
    2. Is it possible that the current limit does not occur even if the maximum value of the current limit is exceeded?

    If yes, what are the possible causes?

    Thank you.

  • 1. Have discussed this with you before. Check whether is the pin voltage or not. I just doubt that your measurement method.

    2. impossible.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.