nRF52832 Output High Voltage - High Drive Spec with low current

[koniho]

I have a sensor HTS221 that I would like to power from an nRF52832 I/O to allow programmatically resetting the sensor. Looking at section 20.4.1 GPIO Electrical Specification we see:

Current consumption of the HTS221 will not be greater than 0.3 mA in all use cases (no use of the heating element) - but the minimum supply voltage is 1.7V. The highlight specification indicates a minimum of VDD-0.4 which for a 1.8V supply bus be insufficient to power the HTS221.

For a design with a 1.8V supply bus, what would the expected output voltage be for a GPIO set to High Drive sourcing 0.3 mA? The information provided in 20.4 is not clear on this. Can we guarantee GPIO output voltage >= 1.7V if current is limited to 0.3 mA?

Thanks!

[Einar Thorsrud]

You do not have a lot of margin, but I think it should be sufficient.

Based on the datasheet numbers you have marked you can estimate an inner GPIO source resistance of something like:

R_source = U / I = 0.4 V / 0.003 A = 133 Ω

Then, if the sensor draws 0.3 mA that would cause a (worst case) voltage drop of approximately:

U_drop = R_source * I_sensor = 133 Ω * 0.0003 A = 0.04 V

That would give you a margin of 0.06 V.

If you want more margin you could always use the GPIO to control an external transistor that could supply the sensor directly, instead of supplying it via the nRF.