CD4541B: CD4541B activated at initial state - Not expected output

Thank you for your answer.

We use this device as a temperature alarm. If the MR is activated, the output is also activated for 14min (the output is connected to several devices' RST and consequently they will decrease their temperature). As you can understand, we cannot have devices that are switched-off during 14min each time after powering up. So how can we avoid this non-defined output? Can we put a pull-up / pull-down at the output? Do you recommend to change the device? Do you know the reference of another one that could do the job?

Thanks in advance,

Nerea

Hi Nerea,

My guess is that the system was designed with the assumption that any latched devices were starting in a known state (LOW is a common assumption, since many latched devices do start LOW more often than they do HIGH).

Part of any system design should be to initialize any latched devices (counters, latches, flip-flops, shift registers, etc). It sounds like the system design would need to be updated - we don't have any direct replacements that include an internal initialization (that's what the MR pin is for).

Hello Emrys and thank you for your answer! Do you mean that if we activate the pin MR during power-up we will have the same output state each time? So, the non-defined output will be now defined thanks to the activation of the MR?

Thanks in advance.

Thank you so much. I have a last question, the datasheet says: ''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''. That means that in our case the MR needs to be activated during 14min? And that the output could no be useful during this time?

Use the SN74HC4060/CD74HC4060 instead.

I do not understand well your answer. Just above, it was mentionned that SN74HC4060 had the same problem as CD4541B regarding the non defined output during power up. So why use this component instead of the original? Regarding the phrase quoted from the datasheet 'setup time [...] '. Do you know something about?

Thanks in adavance.

The SN74HC4060 works similar to the CD4541B (MR is CLR), but it does not do anything special at power up. You can simply keep CLR high during power up.

'Does not do anything special' at power up? Does not have the output non defined at power up or does not need a setup time following initial power up?

The state of the counter is undefined at power up (if not using CLR). It does not have that special setup time requirement.