Which is the driver output impedance of the nRF52832?

[User1321]

I am using the SPI peripheral for communicating with a network through long wires. Is it any information about the impedance of the driver outputs from the nRF52832? I will use this impedance to find the right value of the serial terminating resistor that I'm placing on the network.

Thanks!

[Stian Røed Hafskjold]

Hi, the pin capacitance of the nRF52832 is 3pF. Please see here: infocenter.nordicsemi.com/.../gpio.html

[Stian Røed Hafskjold]

The SPI run current is the peripheral run current + HF clk + regulator run current + DMA bus current. Long story short, about 1.2mA when DCDC regulator is enabled, and 2mA if not enabled.

Then you have the current that drives the capacitive load on the pins which is given by I = f * V * C. So for an 8 MHz SCK, 3V VDD and 4 pF pad capacitance you get 0.1 mA on the SCK pin alone. The capacitive load will highly depend on PCB design. For the nRF5 DK I measured about 40pF, which gives an increase of about 1 mA on the SCK pin when running at 8 MHz.