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LM809: RESET pin

Ivy Jin
Expert 3325 points
Part Number: LM809

Hi team,

When testing the LM809M3-3.08/NOPB, my customer found that its RESET signal would oscillate when power off as shown in the figure.

This issue does not occur if the R627 resistance is removed.

Does this phenomenon have any effect on the operation of the system? and what suggestions do you have for eliminating this oscillation? Is it possible to remove R627? 

Schematic:

The RESET pin waveform after R627 is removed

Thanks!

  • +1
    TI__Expert 5660 points

    Hi Ivy, 

    Thanks for your question!

    This device has push-pull output configuration and if you look at the datasheet for typical application it's okay to remove that resistor.

    Best Regards,

    Sila Atalar 

  • 0 in reply to Sila Atalar
    TI__Expert 3325 points

    Hi Sila,

    Double checked with my customer, the waveform stabilizes when the customer removes the resistance R627 and at the same time cuts off the connection to the DSP reset pin. However, if the reset pin of the DSP is connected, the waveform as shown in the following figure will still appear.

    Do you have any suggestions and whether this situation has an impact on the stability of the system?

    Thanks!

    Regards,

    Ivy

  • 0 in reply to Ivy Jin
    TI__Expert 5660 points

    Hi Ivy, 

    I think removing R627 and adding a zero ohm resistor instead will fix this connection issue, since 0 ohm resistor reconnects the electrical connections. And I don't think R606 is needed since reset output has push pull configuration, so please let them know they can remove R606 also. 

    Regards,

    Sila Atalar