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Greetings,
We are working on NDIR sensors using LMP91051, and have some questions concerning to the operation of the LMP91051.
As a very initial approach, we used LMP91051EVM + SPIO4 board, and it worked fine.
Our next step was to use the LMP91051EVM alone, eliminating SPIO4 replaced by Arduino Uno to send SPI command to the LMP91051, and worked okay.
A problem arose when we soldered the LMP91051 chip on the TSSOP adapter board and constructed a circuit as described in the figure below.
We used 10nF ceramic capacitors for the three capacitors at the left-hand side in the schematic above. VDD was connected to +3.3V without placing any capacitor between, and VIO was just shorted to the VDD (no filtering). CSB was just connected to ground as we have only LMP91051 as a SPI slave. SCLK was provided from the SPI clock of Arduino Uno, and SDIO was connected to the MOSI of the Arduino Uno. (I understood that MOSI_EN of the LMP91051EVM is not necessary if we don't plan to read registers from LMP91051.) We use a DAQ to read the analog output from the OUT pin from the LMP91051.
Unfortunately, we have no luck. The signal does not even show any periodic pattern from %50 duty cycle of the lamp power input.
Any advice would be highly appreciated. Thank you.
Hi Carter Liu,
Thank you for your reply.
Yes! I used default configuration for every options except PGA1 and PGA2 turned on.
As shown above, the output does not seem to show any meaningful sign. But, when the pulsed input (5V, 50% duty cycle) into the lamp of the sensor was disconnected, the output voltage dropped.
Any advice for this problems would be highly appreciated. Thanks.
