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Using an MCU like from MSP430 series, it is possible to create circuits that runs from battery power for years in some standby mode (waiting for button or realtime clock alarm for example).

However, if I for example add an OLED display, that has a specified 'sleep' power of 2mA, this wouldn't work.

How can I prevent the display consuming the battery power on standby? I first thought about switiching the display's GND by a MOSFET, but all other lines (data bus) may source current then, maybe the display even present VCC on the bus pins, if GND is disconnected? The display may source power from the bus pins then, draining the battery again or even destroying the MCU's outputs.

Is there a clean solution? Or do I have to find a display with equally low sleep consumption?

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  • \$\begingroup\$ You should be able to power the OLED via a transistor or MOSFET. Find a component with a low leakage current at the voltages and temperatures that you intend to run the OLED at. \$\endgroup\$ – Dampmaskin May 23 '16 at 11:02
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If the display is running from the same power voltage as the micro, then there is no problem switching the ground side of the display's power. Just make sure that all the micro ports connected to the display are either set to high impedance or driven high.

If the display communicates via a IIC bus, as many do, then switching the low side of the power actually makes things easier. That way there will be no current thru the IIC pullups without you having to switch those separately.

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  • \$\begingroup\$ I see. So the correct procedure would be like 1) set display to sleep mode 2) disengage bus line driving and 3) switch off display GND FET. Powering on again takes all steps in the other direction I guess. \$\endgroup\$ – dronus May 23 '16 at 12:04
  • \$\begingroup\$ @dron: Sounds good. \$\endgroup\$ – Olin Lathrop May 23 '16 at 15:49
  • \$\begingroup\$ I tried low-side switching of an SD card today and it works after some tuning. It gives aggressive transients if power raises or falls and I have to tune the bus-line switching order and timing to get switching on and off reliable without triggering the MCUs brownout condition. Beside this, it is an example for such switching you mentioned and it works. \$\endgroup\$ – dronus Jun 14 '16 at 23:34

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