SN74LVC1G07: Can we power the buffer with voltage divider from 12V and still operate properly?

Hi,

The resistor divider is a great way to do cheap down translation with passive components however it is not so great for powering a device. The buffer you are using is a CMOS device which consumes power from the Vcc pin to drive the outputs. Here is a simplified diagram of the internals of a CMOS gate.

As you see, when the output needs to driven high, the top FET turns on, connecting the VCC pin to your load. At this point current will be drawn into the device from the Vcc pin. If current flows into the device from your fixed resistor divider, then a simple KCL or KVL on the node will tell you that the voltage will not stay fixed but will begin to vary. This will cause the supply voltage on the device to vary causing the output voltage to vary. This is not a desired operating condition and so the resistor divider will not work to power the device. If the current flowing into the device was fixed, then a resistor divider might have been possible.

Thanks!

-Karan

All logic devices have lots of internal buffers. Only the output is open drain.

If you do not have a supply voltage in the 1.8 V… 5 V range, you need a voltage regulator. (And even a cheap TL431 would need less current than that divider.)

And the output (pin 4) must never see 12 V. (I'm mentioning this because the signal has a suspicious name.)