Electronics > Beginners

Need a latching buffer, need help configuring

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jnz:
5V micro. Another device that has an enable line internally pulled up. I need to selectively latch and hold this line low while my micro is off.

I currently have a trace going from my micro to a device and ground when needed, but I can't force the pin to be held low while the micro resets otherwise not running for some time. I can't just permanently hold the line low. Can't use a pull down, as it's internally pulled up, I'm trying to keep quiescent current low.

My thought was to find way to make a latching output I trigger from my micro. I don't really see a great way to do this considering I need HIGH, LOW, and while reset or unpowered my micro's pin will be an input.

Opamp? Transistor pair? Some buffer IC?

David Hess:
It sounds like an application for a set/reset latch which many flip-flops like the ubiquitous 74HC74 can operate as.  It has active low asynchronous set and reset inputs, the clock like can be used as an additional rising edge input to set either output state, and it includes complementary outputs.  Or you can use a pair of NAND or NOR gates configured as a set/reset latch.


mvs:

--- Quote from: jnz on December 29, 2018, 12:03:26 am ---Opamp? Transistor pair? Some buffer IC?

--- End quote ---
If inversion and switching speed are not a concern i would go for small MOSFET (2N7002 or BSS138) and weak pullup.

Zero999:
Sorry I don't understand what you're looking for.

Do you want to hold the pin low for a short length of time after the MCU has been turned on? If so, a simple capacitor to 0V will do that.

fsr:
It seems to me like you need a circuit that pulls the line low, unless the micro pulls it up. The response from mvs looks like a good, cheap way to do that.

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