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CD4541B: Setup Time

Greg Kooser
Prodigy 40 points
Part Number: CD4541B

On page 5 of the specification, it is stated "A setup time equal to the width of the one-shot output is required immediately following initial power up, during which time the output will be high."

If I understand this correctly, if I set a one-shot time to say, 30 minutes, then at power up, that 30 minute pulse will occur, no matter what condition MR is. Is that correct?

Thank you,

Greg

  • 0
    TI__Genius 16725 points

    Hi Greg,

    It  is not possible to set the one-shot time to 30 mins. And yes, the output of the device will be high regardless of the value of MR during this setup time period. The frequency for the RC have to be chosen between 1kHz and 100kHz. This limits the one-shot time and so it wouldn't be able to do 30 minutes.

    Thanks!

    -Karan

  • 0 in reply to Karan Kotadia
    Prodigy 40 points

    I know of the limitation of the internal clock, so am planning to use an external clock.

    Beyond that, I want understand better about the behavior of MR and start-up.

    If I use power applied as a start of the counter, how should I connect MR, or does it matter?

    Can I use power applied to start the counter? I just need 1 positive pulse for some period of time, then have the output go low and stay low until I remove power and reapply it.

    Thanks for you help.

    Greg

  • 0 in reply to Greg Kooser
    TI__Genius 16725 points

    Hi Greg,

    You can use the Auto Reset pin to do what you require.

    Timing is initialized by setting the AUTO RESET input (pin 5) to logic “0” and turning power on. If pin 5 is set to logic “1”, the AUTO RESET circuit is disabled and counting will not start until after a positive MASTER RESET pulse is applied and returns to a low level.

    Do you want the device to pulse high on power up? Then you can just set the AUTO REST to a logic 0 and set the PIN 9 to a High. Then the device output should be high for the count of your output on power up. The Master Reset pin should stay low during this entire time.

    You can always orders some samples to test and verify this operation.

    Thanks!

    -Karan

  • 0 in reply to Karan Kotadia
    Prodigy 40 points

    Karan,

     

    We want to be sure we understand the operation of this device.

    If we tie pins 5 (AR), 6 (MR) and 10 (MODE) to GND and 12 (A), 13 (B) and 9 (Q sel) to VCC and power up the device, the output will go high for the programmed time (Clk Freq/65536 in this case) then the output will go low and stay low until we remove and reapply power.

    Does this sound correct?

     

    Thanks very much for your help.

     

    Greg

  • 0 in reply to Greg Kooser
    TI__Genius 16725 points

    Hi Greg,

    Yes, this is what I expect to have happen since it is what is mentioned in the datasheet. However I would confirm this by ordering samples and testing the device before use. I am sorry for the lack of helpful answer on this question. These are some of our legacy parts that the information is not very clear on.

    Thanks!

    -Karan