Hello, i have a question regarding CD14538B. What if i want the output to stay latch until it is being reset. Should i connect both Cx pin (2,14) and RX,CX pin (1,15) to ground. Or should i just leave them floating ? I cannot find this in the datasheet. Also i tried to connect Cx pin to ground and leave Rx,Cx pin floating. It seems to stay latch but sometimes it does not after a period of time.
Thank you!
Hi mtpham0912,
I am not 100% certain on this, but I don’t believe you can latch the CD14538B in the “latched ON” state. The only way to keep the output high is to send more trigger pulses (low-to-high (positive edge) transitions on “+TR” or high-to-low (negative edge) transitions on “-TR”) before the time-out period. At first I was thinking one might be able to feed back the output to the input to keep it latched on, but this would only provide a steady-state high signal rather than the required positive or negative edge required to retrigger.
I think you’ll need a different part to get your resettable latch. One such possibility might be an S-R flip-flop. We carry several J-K flip-flops with S-R functionality which could be used for this function. For your application, you would tie your input to the “Set” pin and your reset to the “Reset” pin. All other unused inputs should be tied to either Vdd or Vss. Then, the output, “Q”, will go High whenever your input is High and remain latched until Reset is invoked (unless “Set” is still high, in which case Q would remain High).