MCUXpresso SDK Documentation
Open on Repo Open an Issue
Source (.md/.rst) Page PDF (.pdf)

opamp_fast_lpadc

opamp_fast_lpadc#

Overview#

The OPAMP single lpadc example demonstrates how to use the OPAMP driver. In this example, the reference voltage (Vref) of the OPAMP non-inverting input port comes from the VDD, the OPAMP inverting input port needs to be connected to a voltage source and an LPADC channel, the OPAMP non-inverting input port needs to be connected to GND, and the OPAMP output port needs to be connected to an LPADC channel.

When this example runs successfully, the terminal will print the OPAMP output port voltage value, the OPAMP inverting input port voltage value, and the theoretical OPAMP output value.

The theoretical calculated value should be very close to the value measured by LPADC.

OPAMP input and output relationship formula:

  1. Inn=Vp+(Vout-Vp)*Rfb1/(Rfb1+Rfb2)=Vp+(Vout-Vp)/(gain+1)

  2. Inp=Vn+(Vref-Vn)*Rfb1/(Rfb1+Rfb2)=Vn+(Vref-Vn)/(gain+1)

  3. inn=inp => Vpgain+Vout=Vngain+Vref, Vout=Vref-(Vp-Vn)*gain

Supported Boards#

FRDM-MCXA174
Hardware requirements

  • Type-C USB cable

  • FRDM-MCXA174 board

  • Personal Computer

Board settings Please connect OPAMP1 positive input channel (SJ2-3) to the GND. Please connect OPAMP1 negative input channel (SJ3-3) to a voltage source. Please connect OPAMP1 negative input channel (SJ3-3) to J2-9.

Prepare the Demo

  1. Connect a micro USB cable between the PC host and the MCU-Link USB port on the board

  2. Open a serial terminal with the following settings (See Appendix A in Getting started guide for the description of how to determine serial port number):

    • 115200 baud rate

    • 8 data bits

    • No parity

    • One-stop bit

    • No flow control

  3. Download the program to the target board.

  4. Either press the reset button on your board or launch the debugger in your IDE to begin running the demo.

Running the demo

Opamp lpadc example. Please press any key to get opamp output value. Opamp output voltage = 818mv Opamp negative input voltage = 80mv Opamp theoretical output value = 903mv Opamp output voltage = 611mv Opamp negative input voltage = 100mv Opamp theoretical output value = 699mv Opamp output voltage = 416mv Opamp negative input voltage = 120mv Opamp theoretical output value = 495mv

Note: the OPAMP1 maximum output voltage is 3.1v, users need to pay attention to the input voltage value of the negative channel.
For FRDM-MCXA174 board:
Inp = Vp + (Vdd - Vp) * 980 / (20000 + 980)
Inn = Vn + (Vout - Vn) * 980 / (10000 + 980)
Inp = Inn, VDD is about 3287mv.

1. Set opamp negative input to 80mv, opamp theoretical output value is about 900.
2. Set opamp negative input to 100mv, opamp theoretical output value is about 700.
3. Set opamp negative input to 120mv, opamp theoretical output value is about 500,

Slight changes in VDD, input voltage, peripheral circuits, the offset inside the OPAMP, and the LPADC measurement error will cause
a difference between the theoretical value and the actual value. A difference within 100mv is considered normal.
FRDM-MCXA344
Hardware requirements

  • Type-C USB cable

  • FRDM-MCXA344 board

  • Personal Computer

Board settings Please connect OPAMP1 positive input channel (SJ2-3) to the GND. Please connect OPAMP1 negative input channel (SJ3-3) to a voltage source. Please connect OPAMP1 negative input channel (SJ3-3) to J2-9.

Prepare the Demo

  1. Connect a micro USB cable between the PC host and the MCU-Link USB port on the board

  2. Open a serial terminal with the following settings (See Appendix A in Getting started guide for the description of how to determine serial port number):

    • 115200 baud rate

    • 8 data bits

    • No parity

    • One-stop bit

    • No flow control

  3. Download the program to the target board.

  4. Either press the reset button on your board or launch the debugger in your IDE to begin running the demo.

Running the demo

Opamp lpadc example. Please press any key to get opamp output value. Opamp output voltage = 818mv Opamp negative input voltage = 80mv Opamp theoretical output value = 903mv Opamp output voltage = 611mv Opamp negative input voltage = 100mv Opamp theoretical output value = 699mv Opamp output voltage = 416mv Opamp negative input voltage = 120mv Opamp theoretical output value = 495mv

Note: the OPAMP1 maximum output voltage is 3.1v, users need to pay attention to the input voltage value of the negative channel.
For FRDM-MCXA344 board:
Inp = Vp + (Vdd - Vp) * 980 / (20000 + 980)
Inn = Vn + (Vout - Vn) * 980 / (10000 + 980)
Inp = Inn, VDD is about 3287mv.

1. Set opamp negative input to 80mv, opamp theoretical output value is about 900.
2. Set opamp negative input to 100mv, opamp theoretical output value is about 700.
3. Set opamp negative input to 120mv, opamp theoretical output value is about 500,

Slight changes in VDD, input voltage, peripheral circuits, the offset inside the OPAMP, and the LPADC measurement error will cause
a difference between the theoretical value and the actual value. A difference within 100mv is considered normal.
Contents