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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

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    \$\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\$
    – Peter Smith
    Feb 28, 2021 at 14:32
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    \$\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
    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
    Feb 28, 2021 at 19:01
  • \$\begingroup\$ I have doubts your MMBT2222 circuit was working at all at 200ns cycle. \$\endgroup\$
    – Spehro Pefhany
    Feb 28, 2021 at 20:31

2 Answers 2

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A 900 nA static current is ok for your application?

https://assets.nexperia.com/documents/data-sheet/74AUP2G14.pdf

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

https://www.ti.com/lit/ds/symlink/sn74hcs14.pdf

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    \$\begingroup\$ +1. Custom silicon will beat any discrete solution in this regard. \$\endgroup\$
    – winny
    Feb 28, 2021 at 15:10
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Most power efficient way would be in software, if you are driving or observing these signals in an MCU.

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