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LP2989 accidentally designed a connection to pin2 n/c. Will it be a problem?

Robert Horton
Prodigy 40 points
Other Parts Discussed in Thread: LP2989

In an existing product we have had to replace  a regulator with the LP2989 which is pin for pin compatible except pin 2. The original regulator used pin 2 as a programmable delay on time. It would source 2.2uA and had a capacitor (1uF) connected to it. The capacitor would then take a specific time to charge up with the constant current.

The LP2989 does not have a programmable delay on time and pin 2 is listed as n/c "do not connect to this pin". Unfortunately the 1uF capacitor is still fitted to the board and connected to pin2. Will this be a problem?

Thanks

  • 0
    TI__Mastermind 22610 points

    The LP2989 pin 2 is used for post-assembly trim of the output voltage during final test.

    Q: "Will this be a problem?"

    A: Probably not a problem for most applications.

    Worst case is that the internal trim was not activated, so there will be a few hundred milli-secs (RC = 1uF x ~200k) for Vout to go from ~99% ot the final Vout to 100% of the final Vout as the 1uF capacitor charges through the internal feedback resistor array. The first ~99% of Vout will be normal start-up.

    Best case is that the internal trim was activated and this pin is now internally connected to ground through a few ohms, and there is very minimal (almost zero) charge going to the 1uF capacitor. In this case, the first ~99.99% of Vout will be normal start-up

     

  • 0 in reply to Donald Jones
    Prodigy 40 points

    Thanks for the information