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CD4536B: On-Delay Timer

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. 


Tim Jager

  • 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?
  • 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?
  • 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. 


    Tim Jager

  • If VCC = 3.3 V is possible, what about a complete oscillator chip running at 1 Hz, and a divide-by-N counter?