Posted on January 23, 2013 at 22:30Hello,
I use external reference voltage connected to Vref+ pin to improve ADC accuracy. This is precise voltage shunt with resistor connected to voltage supply (typical configuration for detail see doc LM4040 for example). My apllication is power consumption sensitive so I switch uC to halt mode for most of running time. But external reference voltage consume a lot of current so I have to switch off this reference from power supply when uC is in halt mode (cut off voltage shunt`s resistor from supply by transistor). The main problem is when I do this current consumption in halt is about 60uA instead of about 3uA max. After some investigation I find that ''victim'' is voltage on float Vref+ pin. This voltage is shunted by external reference and consume about 55uA. This is true according with shunt documentation. But why on floating Vref+ pin is voltage? (no information in doc). To solve this problem I design more complicated switch off circuit but my question is if there is possibility to software switch off voltage on float Vref+ pin. I don`t find any notice in uC documentation about this. If someone struggle with similar issue and solve it by software way I will be very aprreciate for information. I search all STM8L documents but maybe I missed something.
BR
DJ
