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LM2611EVAL: Instability issue

Jab
Prodigy 110 points
Part Number: LM2611EVAL
Other Parts Discussed in Thread: LM2611

Hi,

For our validation, we wired the LM2611EVAL board according to the schematics below. After connecting the load to the EVM, we are experiencing the problems described below.

  1. For maintaining the power sequence, we provided an RC network as shown above schematics. When the RC connected to the ground from the input as shown in the schematic, the voltage across the input voltage and SHDN voltage became 1.6V. However, when the RC network is connected to the Vout, the input voltage is 12.5V. This kind of problem was not seen when providing the 5V input voltage. Can someone explain why this problem happens when the RC is connected to the ground?
  2. After connecting the RC network to Vout, the EVM board is functioning correctly. On the EVM board, we are facing an issue that, when taking a load, the regulator's output occasionally drops to -6V. Although this problem doesn't happen very often, it appears inconsistent. Only when we provide an input voltage of 12.5V do we run into this problem. When using a 5V input, we did not see this problem. Does anyone know why this is happening?, Our product's load current is <50 mA.

Thanks,

Jab

  • 0
    TI__Guru 51451 points

    Hi Jab,

    thank you for using the E2E forum.

    If I understand right, you tried to connect the top side of the resistor connected to the SHDN pin of the LM2611 to the output (expected to be -13V when powered up)

    In this case please note: the SHDN pin expects a positive voltage to enable the device 

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    TI__Guru 51451 points

    Hi Jab,

    I have not seen up update on this thread for 14 days.

    So, I assume the issue is solved and i will close this thread.

    In case there is still something open, just reply to reopen or start a new thread.

    Best regards,

     Stefan