TCL555CP: Repeated Timer Failures in Circuit

We experienced similar issue - about five out of ten TLC555CP parts got hot and did not work.  Power to ground measured about 15 Ohms.  The circuit was copied from Figure 22 of TI Ap Note SLFS022I (2014).  The RC was adjusted to have about 16.5ms.  The applied voltage was 15V.

After experience above, we tried just first stage alone.  The output pulse changes everytime when Trigger was grounded momentary via toggle-push switch.  The pulse width varied from 200 to 280 ms typically instead of 16 ms.

The part marking is 69AFNPM, TLC555CP.

Thanks.

5 Replies

  • Michael,

    Post split from thread:

    This circuit needs a pull up resistor for the input switch.

    TLC555 requires a clamp diode to prevent 30V transients on second trigger input.

    Which TLC555 are being damaged, just the first timer or do other timers in the chain get damaged?

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Thanks for quick reply, Ron.

    First time, we did not have pull up on the first 555 and no diode installed.  First 555 and third 555 got damaged - their VCC to GND read about 15 Ohms.

    Second time, with pull up and no diode, second 555 (middle one) got damaged with its VCC to GND read about 15 Ohms.

    Third time, just the first 555 CIRCUIT alone (first stage), output varied ~ 200 - 240 ms every time push switch toggles.  The RA and CA values were 15k and 1 uF - expect for 16.5 ms. 

    Thanks.

  • In reply to michael MAI:

    Michael,

    I was thinking about ESD damage from push button or the cabling (if any) to the switch. However, this wouldn't affect 2nd and 3rd timers.
    All timer use the same VCC power. 15V is fine, but does the supply have transients or hotplugging?

    For the long time period, I suspect leakage on the threshold pin that increases the charge time of the external capacitor.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    I checked a few samples and did not see any sensitivity to short term excessive VCC voltage. I recorded total ICC vs VCC (and observed output) for a-stable and mono-stable setup. [RA=RB=16.2k, C=10nF].

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Hello Ron,

    Thanks for your support.  The first time, first stage and third stage timers got damaged.  The second time, second-stage timer got damaged.  FYI - at this time, I am working on something else.  Not sure when I will have new updates.

    Regards.