FRDM-MCXA156 lpdac opamp lpadc example
Overview
In this example: 1. The LPDAC outputs a 300mv voltage to the non-inverting terminal of the OPAMP.
2. The OPAMP operates in the non-inverting amplifier mode, the inverting terminal of the OPAMP is grounded.
3. The channel 0 of the LPADC is connected to the output of the OPAMP, and the channel 1 of the LPADC is connected to the output of the DAC (the non-inverting input terminal of the OPAMP).
4. The ideal sampling range of OPAMP output channel is specified by ‘ideal-sample-range’, and ‘nxp,opamps’ is used to specify LPADC samples which OPAMP’s output and which ADC channel is connected to the OPAMP output.
5. The OPAMP non-inverting input is 300mV, and the OPAMP gain is initialized to 1. Therefore, the first round OPAMP output (~300mV) will not reach the minimum value of the ‘ideal-sampling-range’. Therefore, the ADC driver will increase the OPAMP gain through ‘opamp_set_gain’. The second round OPAMP output (~900mV) is still below the minimum value, so the gain will continue to increase. The third round OPAMP output (~1500mV) is already in the ideal range, so the gain will not be adjusted later.
Building and Running
Build the application for the FRDM-MCXA156 board.
west build -b frdm_mcxa156 samples/boards/nxp/frdm_mcxa156/lpdac_opamp_lpadc
west flash
Hardware connection (OPAMP0 in differential mode): 1. OPAMP positive input channel J2-12 connects to DAC0 output J2-9, and LPADC0 channel 1 input J4-2. 2. OPAMP negative input channel R60-3 connects to GND. 4. Vout = Vinp * (Ngain + 1), if Ngain > 1; Vout = Vinp * Ngain, if Ngain = 1.
Sample output
You will see the raw data and voltage of the opamp non-inverting input (DAC output voltage) and the raw data and voltage of the opamp output in the terminal.
*** Booting Zephyr OS build v4.2.0-3573-gd796bf703856 ***
round 0: output=5796 (~291 mV), input=5949 (~299 mV)
round 1: output=17806 (~896 mV), input=5945 (~299 mV)
round 2: output=29506 (~1485 mV), input=5964 (~300 mV)
round 3: output=29508 (~1485 mV), input=5957 (~299 mV)
round 4: output=29529 (~1486 mV), input=5944 (~299 mV)
Note
The values shown above might differ.