Clamping diodes and series resistor

MateusGL
Posts: 10
Joined: Sun Feb 23, 2020 5:18 am

Clamping diodes and series resistor

Postby MateusGL » Fri Jul 03, 2020 3:45 pm

Hi,

I'm working in a project where sometimes the ESP supply will be 3V, but the ESP will receive digital signals of 3.3V. In the datasheet the limit is VDD+0.3V, so if the ESP supply is 3V, signals with 3.3V are OK, but the supply can be a little less, like 2.9 or 2.8V, then 3.3V signals will be higher than the datasheet limit.

Are there clamping diodes in ESP inputs? What should be the maximum input current when the diodes are clamped? My ideia is to put a series resistance to limit the current and avoid damages to the ESP if the signal voltage is a little higher than VDD+0.3V.

ESP_Sprite
Posts: 3759
Joined: Thu Nov 26, 2015 4:08 am

Re: Clamping diodes and series resistor

Postby ESP_Sprite » Fri Jul 03, 2020 8:18 pm

I think technically they are snapback devices instead of clamping diodes, the idea is the same. However, officially we do not advise putting any voltage over what's stated in the datasheet on the GPIOs. For the few hundred millivolt, however, you could make a small resistive divider (1K/10K or so) and neatly be within range of the values indicated on the datasheet. (Unofficially, I doubt much will go wrong if you only put a series resistor of, say, 1K in line with the IOs, but I can't advise that officially for production use.)

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