I am designing a IoT PCB that will be powered with a Li-ion battery. I need to be really thoughtful about how much current will be drawn by the entire circuit, in order to increase battery life.

I've got 4 signals to and from the MCU that needs to go be inverted:

  • /CS pin of SPI communication (5MHz, 200ns period)
  • /INT interrupt output of a device
  • /SIGNAL of a pushbutton
  • CTRL control signal of a device

I need to invert these signals because my MCU can only be woken up from sleep by rising edge/high level GPIOs, so software inversion is not an option.

What would be the best way to invert these signal while being mindful of power consumption, size, and cost? Usign a NPN transistor? Using a N-channel MOSFET? or using a dedicated inverter logic gate chip?

Initially I designed a NPN inverter circuit with a mmbt2222 but the value of the base resistors, collector pull-up, and input pull-up or pull-down had a massive negative effect on power consumption.

Thank you all

  • 3
    \$\begingroup\$ Why do you need to invert the signals? If they are feeding CMOS inputs then the leakage current is tiny anyway. That said, a CMOS inverter is probably the best way to go. \$\endgroup\$ Commented Feb 28, 2021 at 14:32
  • 1
    \$\begingroup\$ If you have a microcontroller then why you are not creating a inverted signal? And if you still need to invert those signal, use CMOS inverter IC. Otherwise you can use OP-amp inverting comparator. \$\endgroup\$
    – Sadat Rafi
    Commented Feb 28, 2021 at 15:16
  • \$\begingroup\$ Most likely the CMOS logic gate. But I am a bit shocked to hear that you are expecting SPI CS to toggle at 5 MHz. How fast is the SPI clock? \$\endgroup\$
    – user57037
    Commented Feb 28, 2021 at 19:01
  • \$\begingroup\$ I have doubts your MMBT2222 circuit was working at all at 200ns cycle. \$\endgroup\$ Commented Feb 28, 2021 at 20:31

2 Answers 2


A 900 nA static current is ok for your application?


This one has a higher worst case (2uA, 100nA typical), but you would need only one IC:


  • 1
    \$\begingroup\$ +1. Custom silicon will beat any discrete solution in this regard. \$\endgroup\$
    – winny
    Commented Feb 28, 2021 at 15:10

Most power efficient way would be in software, if you are driving or observing these signals in an MCU.


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