Photodiode/UV sensor
UM1955
12/28
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.
