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Original question:

TPS2121: TPS2121 Drop Out

TPS2121: output drop in xref

Ben Kuo
Expert 7550 points
Part Number: TPS2121

Dear Team,

Customer design their buck up system with our TPS2121 in XREF mode. 

They face to output voltage drop during plug in-out test. please refer to waveform in attachment.

TI is normal waveform: plug in IN1-->voltage go high-->remove IN1-->voltage go down to IN2 voltage level

T2 with issue:  plug in IN1-->voltage go high--> remove/plug in/remove IN1 in the short time --> expect IN2 will provide to output but output drop down.

Could you contact me off-line and I can share customer's schematic with you? thanks

Ben

  • 0
    TI__Genius 13760 points

    Hi Ben,

    Thank you for reaching to the E2E forum!

    I believe I know what is going on here but I will need a little more information on the waveform to verify. I don't believe I need to look at the schematic just yet, but would you be able to ask the customer if they can provide a waveform of this event with the following signals: VIN1, VIN2, and VOUT. These are the important signals I need, but if they could also include ST signal it would be great.

    Regards,

    Andy Robles

  • 0 in reply to Andy Robles
    TI__Expert 7550 points

    Hi Andy,

    Thanks for your support.

    Here is IN1(CH1)/IN2(CH2)/ST(CH3)/output(CH4) waveform.

  • 0 in reply to Ben Kuo
    TI__Genius 13760 points

    Hi Ben,

    From my understanding the device is behaving properly when IN1 and IN2 are present. In this scenario the TPS2121 will select IN1 to be the output source.

    When you remove IN1 the device switches off to IN2 and performs as expected. Once you plug IN1 back in, the TPS2121 switches back to IN1 as the output source correct?

    The issue is seen when IN1 is removed/plugged-in/removed very fast. I have a couple questions and comments regarding this event:

    1. How is the customer performing this remove/plug-in/remove behavior?

    2. How long does it take from when IN1 is removed the second time to when the TPS2121 ramps up to IN2?

    3. Do you have an output capacitor on the TPS2121?

    4. How much current is being pulled by the load?

    5. Judging by the duration of the voltage dip, the device seems to be turning off by one of its protective features (over current protection or over temperature protection)

    Best regards,

    Andy Robles

  • 0 in reply to Andy Robles
    TI__Expert 7550 points

    Hi Andy,

    Thanks for your information. Please let me know if you find any risk from our feedback or not.

    1. How is the customer performing this remove/plug-in/remove behavior?

    - They do it by manual to simulate bad connection. 

    2. How long does it take from when IN1 is removed the second time to when the TPS2121 ramps up to IN2?

    - IN2 is always connected, only change IN1 connection status. 

    3. Do you have an output capacitor on the TPS2121?

    - 220uF bulk cap

    4. How much current is being pulled by the load?

    - 12V@1A load current

    5. Judging by the duration of the voltage dip, the device seems to be turning off by one of its protective features (over current protection or over temperature protection)

    - RLIM is set as 30K-ohm, I will double confirm if inrush current trigger to OCP or not.

  • 0 in reply to Ben Kuo
    TI__Genius 13760 points

    Hi Ben,

    Can we continue this conversation via email. I would like to take a look at the customer schematic. You can reach out to me at a-robles@ti.com.

    I will go ahead and close this thread for we will continue this conversation via email.

    Best regards,

    Andy Robles