CD4541B: The outputs of 2 timers are out of sync

Hey Dorson,

Is there any particular scenario or set up that you can think of that could be correlated to when you see the issue? Or does it just seem completely random? I don't see the right output going high in the scope shot, can you tell me how out of sync they are when the issue happens?

Hey Dylan 

   It doesn't happen randomly .After I power off  ,then  recyle the power on within 5 seconds ,it would auto reset and output high level signal .But you know I have pulled up the AR pin to high voltage that means Auto-reset is disable .I shouldn't auto reset .

    If I wait for more than 5 seconds and then power on ,it never appears auto reset .I have no idea what cause it happen.

    it seems it needs more time to dicharge .Do you have any solution to help me fix the discharge problem ,if it is reason .

    Many thanks 

Hey Dorson,

Whats the state of your master reset pin during this time?

Hi Dylan 

At the first time ,I supply the power line 5V-PWM signal ,the MR Pin 's wave form is PWM .and then power off.  3 seconds later, I power on with 5V DC to power pin ,at this time MR pin with low level .     but Q-Out output high level for 415mS that's what the delay time I setup .

But If I power on with 5V DC after 6s later .The Q-output ouput low level .

It looks like it needs 6s to discharge .

could you help mei to fix it ?

I have take shotscreen in attachment 

Thanks 

4541 problem.docx

HI Dylan 

   I have tried to supply DC voltage to the VDD and MR ,but within 6s I power on again (but no high voltage to MR) ,   Q  still outputs high level for 415mS which is the time I  setup.

   Do you have any comment ?Thanks 

4541 problem - update.docx 

Hey Dorson,

Thanks for the details, I'm currently doing some digging to see if I can find any design files that may help us here. Please give me until early next week to provide you with some feedback. In the meantime if you have additional findings, feel free to post them and i will review those as well.

Hey Dorson,

Due to the age of the device and acquiring it from Harris, i was unable to find any design schematics to help here, but i went back and review the schematic again. I did notice that you have the Q output selection incorrect for what is written there, it should be at GND but you tie it to Vcc. This means the device will power up with a High output initially. I notice on the new scope shot that it does this and returns low, however it should not do this unless there is a reset happening. On top of that the counting wil only start after the MR pin has returned low which really isn't happening correctly since it is tracking the supply during power off. There may be some race conditions happening with the reset circuitry causing this weird issue. Also, as mentioned in the data sheet this issue can be made worse by not having a Vdd greater than 5 V since it will cause a less reliable power-on reset. It may be better for you to use the AR feature and keep the MR pin held at GND.