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I have an MCP73831 li-ion charger connected to an ATMega1284p. The charger has a tri-state status pin which can be High(5V), Hi-Z or Low. The ATMega runs at 3V3.

I want to be able to read the value of the tri-state. I don't need to discern between Hi-Z and High. I was thinking of using a 1.8V zener like so:

schematic

simulate this circuit – Schematic created using CircuitLab

Will this work? And what do I need to be aware of?

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  • \$\begingroup\$ Are you using a zener to drop 5 V -> 3.3 V or 3.3 V -> 1.8 V? \$\endgroup\$ – winny Nov 4 '16 at 12:38
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Yes, it should work. You don't really need the zener though. In the low state any diode will pull the input low, although it is eating up the input noise margin. When the output is high or Hi-Z very little current is going to flow through the diode, zener or small signal. The zener depending on tolerances will actually cause the input to go a little higher since it getting close to breakdown. A signal diode, properly chosen will let only leakage current through keeping the input at a little lower voltage.

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