what should the output be for this use case of the CD4047 chip?
Hello, I am trying to use a CD4047 in monostable, positive-edge trigger mode:
I am not skilled enough to make out what the output, i.e. pin 10, should be when pin 8, the input, is held at 0V (0.1V for some reason). Would expect it to be 0V, I am getting Vdd instead. Is this to be expected? Tried with two chips from different manufacturers bought from different stores.
My diagram:
P-MOSFET: FQP17P06 TVS diodes: P6KE18A (Schottky) Diodes: SBCT2040
I am pretty sure everything has been wired correctly; tried on an Arduino UNO @ 5V and car battery @ 12V; I did measure pin 8, input, to be some 0.1 V in the absence of the T signal.
This is getting quite weird. I have been poking at one of the circuit boards doing voltage measurements, putting the B and T signals to 0V / 5V / rectangular 0 -> 5V, it has started working as expected. I have then taken the second board, that one too has started to work as well. Some more fiddling later and only one kept working as expected.
Some hours later and I think both chips are fine. Quitea few cold joints... I am going to retry them both PCBs on the 12V vehicle setup.
1 answer
Possibly it is damaged. Be ESD aware and do not power up with any voltage on any pins > 0.5V (Latchup failure)
If raising p9 (reset) does not lower Q to logic "0"=<20% Vdd) replace the IC.
No sweat, be more careful next time for handling failures of ESD etc. Most new IC failures are handling issues or over voltage on power-up which causes excess junction heat from shoot-thru Pch to Nch both ON at the same time.
This is the most direct way to test / reset the output.
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