Photodiode/UV sensor

UM1955

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DocID028405 Rev 1

resistor. When current is flowing through a resistor which has a large value, it is mandatory

to use an operational amplifier with a very low input current offset. This is why operational

amplifiers with a CMOS input stage, such as the TSU104, are required.

5.4

Additional possible use

With this configuration it is also possible to connect a UV (ultraviolet) sensor in order to

derive the UV index instead of ambient light. A free footprint is available on the expansion

board to enable this possibility.

Note that if using a UV sensor, R26 should be aligned to the UV sensor datasheet

recommendation and the photodiode must be removed.

For additional details on the analog conditioning circuit used for a high impedance sensor

and especially on a UV sensor, refer to application note AN4451 “Signal conditioning for a

UV sensor”, available on www.st.com.