I'm using a CD4504B level shifter to translate 5V signals to 12V.
However, the 5V power supply is not always present...
... and I have the impression that the device is doing stupid things (high power consumption, and output switching unexpectedly (at least it happened once...)).
I have pull-downs on all the inputs, so I presume they should not disturb the CD4504B, but I can find no information about what is supposed to happen when VCC = 0 and VDD = 12V...
I have pull-downs on all the inputs, so I presume they should not disturb the CD4504B, but I can find no information about what is supposed to happen when VCC = 0 and VDD = 12V...
Crazy and unpredictable things will happen if any of the inputs have more than 0.5V on them when VCC=0. Check "INPUT VOLTAGE RANGE, ALL INPUTS" on page 1 here and replace VCC with 0.
Thanks for your reply.
Indeed I was careful about this, and I put pull-down resistors on all the inputs. As Vcc is ~ 0, they should be at the same level.
I wonder if strange things happen inside the CD4504B??
I wonder if strange things happen inside the CD4504B??
Possible. Notice that VCC=0 is allowed in its maximum range but nowhere in the data sheet (both graphs or tables) is there any results or comments for this mode - not even for VCC=3.3V. This is older CMOS technology and it doesn't appear to be a normal mode of operation. It could also be a defective chip.
It is not a defective chip because I have measured the same problem with several boards...
Looks like some internal CMOS switch is switching by itself...
It is an ultra low-power Arduino-based board. Whenever the 5V is not needed to run the firmware, I completely shut down the power (thereby switching off the regulator as well...). I try to avoid consuming from my 12V source, so almost nothing is connected to it, except this CD4504B...
So in sleep mode, everything is sleeping, and this stupid level shifter starts slowly to pump more and more current (it takes ~ 1mn to stabilize to ~ 5mA, whereas my circuit normally consumes less than 0.15 uA (yes micro Amps !).
Yes, A PNP, emitter to 12V. PNP Collector is to Sw 12V.
PNP Base to a 10K resistor to +12V and to a 1K resistor to the collector on an NPN transistor Ground the NPN emitter and a resistor from the NPN base to Sw 5V and a 10K from the NPN base to ground..
Turning on the NPN turns on the PNP which switches 12V from it's emitter to it's collector (Sw 12V)
Basically you suggest to switch off the 12V when 5V is not there.
OK, that may be a solution (BTW, I'm a digital guy, I use MOSFETs to gate power, so it would need one N and one P ).
More generally, do you think that it is intrinsically wrong to not power one power domain of a level shifter?
Basically, the resistor on the led side can be dropped, + to positive (from the logic shifter ic) while ground is switched depending on the 5v signal, no signal the IC is powered down.
