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I am designing a board based on the Atmega328P microcontroller. For this controller there is an ISP connector for programming. This connector has the following pins: MOSI / MISO / RST / SCK.

There is a task to protect this tire from electrostatic discharges.

To protect IO / I2C / UART, I use NUP4114.

Scheme:

enter image description here

enter image description here

It is designed to protect several IOs simultaneously.

Question: Is using the NUP4144 in the circuit above suitable for ISP / SPI line?

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    \$\begingroup\$ It is suitable for any speed of 5V logic \$\endgroup\$
    – Tony Stewart EE75
    Oct 9, 2019 at 13:08
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    \$\begingroup\$ @SunnyskyguyEE75 "Any speed of 5V logic" could be misleading. We could agree on that NUP4114 is suitable for the proposed application (ISP Programming of ATMEGA328P) \$\endgroup\$
    – Stefan Wyss
    Oct 9, 2019 at 14:05
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    \$\begingroup\$ Yes, you can use the NUP4114 for 3.3V logic. \$\endgroup\$
    – Stefan Wyss
    Oct 9, 2019 at 14:06
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    \$\begingroup\$ digikey.ca/products/en/circuit-protection/tvs-diodes/… \$\endgroup\$
    – Tony Stewart EE75
    Oct 9, 2019 at 14:11
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    \$\begingroup\$ What is "ISP"? If it is SPI, then call it SPI. \$\endgroup\$
    – Lundin
    Oct 9, 2019 at 14:43

1 Answer 1

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The NUP4114 has very low capacitance, in the 0.3pf range. It also shows that the NUP4114 working on differential lines at 500Mhz. Since SPI, I2C and Uarts don't operate at this speed, it's safe to say that the NUP4114 would not affect signals under 100MHz and would be fine for what you described.

The GPIO capacitance of most microprocessors is much higher, usually 10x higher, so I wouldn't worry about adding this part to digital lines of low speed (under 50MHz).

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  • \$\begingroup\$ Thank you for the answer! \$\endgroup\$
    – Delta
    Oct 10, 2019 at 12:45

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