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CD4536B: On-Delay Timer

tim jager
Prodigy 120 points
Part Number: CD4536B

1. Although the datasheet only mentions an RC option, can the oscillator circuitry be configured to utilize a 32.768 kHz crystal?  The internal oscillator circuitry seems similar to other devices in the 4000 series that support both RC or crystal oscillator configurations. 

2. Does anyone know how to properly configure this IC to operate as a ~30 second On-Delay timer? For example, when the circuit is powered on, the output will be low and will stay low for 30 seconds.  After the 30 seconds has elapsed the output will go high and stay high forever. 

Thanks, 

Tim Jager

  • 0
    Guru 243910 points
    This device does not support a simple crystal. You could use an external clock, i.e., a complete crystal oscillator.

    What does "~30 second" mean? How accurate does it need to be?
  • 0
    TI__Guru* 96591 points
    Hi Tim,
    You could configure this device to provide a set delay, and the accuracy could be fairly high, but it seems like overkill for a 30s on-delay. Have you considered using just an RC circuit with a comparator?
  • 0 in reply to Clemens Ladisch
    Prodigy 120 points

    The application requires a delay that must always be greater than 30 seconds, but could be up to 35 seconds.  It should be repeatable within 1 second. It will operate in a wide temperature range -40C to 85C, so temperature drift could be a concern for RC oscillators.  Another concern is that we would like the timing to be tolerant to supply voltage changes.  An RC oscillator may work if we use precision resistors and NP0/C0G capacitors, though it could be difficult to know if the PCB assembler replaces the precision capacitors for lower quality parts. This will require greater scrutiny and production testing. A crystal oscillator seems like a more repeatable solution. 

    Also, using a microcontroller is not allowed in this application. Otherwise that would have been the simplest solution. 

    Thanks, 

    Tim Jager

  • 0 in reply to tim jager
    Guru 243910 points
    If VCC = 3.3 V is possible, what about a complete oscillator chip running at 1 Hz, and a divide-by-N counter?