CN-0545 is a completely an integrated 0.1°C thermistor measurement system based on a low power, low noise, integrated 24-bit Σ-Δ analog-to-digital converter (ADC). The system can achieve high resolution, low non-linearity and low noise performance as well as very high 50 Hz and 60 Hz rejection. For temperatures in the range of -50°C to +150°C, thermistors provide an excellent combination of sensitivity, accuracy, cost, and simplicity.
The AD7124-4 can be configured for 4 differential or 7 pseudo differential input channels, while the AD7124-8 can be configured for 8 differential or 15 pseudo differential channels. The on-chip programmable gain array (PGA) ensures that signals of small amplitude can be interfaced directly to the ADC. The system integrates several important system building blocks required to support thermistor measurements, including the constant current source, programmable gain amplifier (PGA), internal reference, and the analog and reference input buffers ideal for resistance measurements. This allows direct interface with the sensor, greatly simplifying the design while reducing PCB size, cost and power consumption.
Several options of the on-chip digital filtering, integrated diagnostics, and three power modes provide application flexibility. The current consumed in low power mode is only 255 µA and 930 µA in full power mode. In power-down mode, the complete ADC along with its auxiliary functions are powered down so that the device consumes 1 µA typical. The power options make the device suitable for battery powered applications, loop powered application, and non-power critical applications.
The device also has a power down option. In power-down mode, the complete ADC along with its auxiliary functions are powered down so that the device consumes 1 µA typical. TheAD7124-4/AD7124-8 also has extensive diagnostic functionality integrated as part of its comprehensive feature set.
This user guide will discuss how to operate the EVAL-AD7124-4SDZ/EVAL-AD7124-8SDZ (CN-0545 Evaluation Hardware), the EVAL-SDP-CB1Z (SDP-B) and the AD7124_EVAL+ Software. A complete design support package for the CN-0545 evaluation material containing schematics, layouts (native and Gerber), and bill-of-materials can be found at: CN0545-DesignSupport.
A complete software user guide for the AD7124-4/AD7124-8 and the SDP board can be found in the EVAL-AD7124-4SDZ/EVAL-AD7124-8SDZ user guide and the EVAL-SDP-CB1Z User Guide. Software is required to interface with the hardware. This software can be downloaded from ftp://ftp.analog.com/pub/evalcd/AD7124. If the setup file does not run automatically, double-click setup.exe from the file. Install the evaluation software before connecting the evaluation board and SDP board to the USB port of the PC to ensure that the evaluation system is correctly recognized when connected to the PC. After the evaluation software installation is complete, connect the SDP board (via Connector A) to the EVAL-AD7124-4SDZ/EVAL-AD7124-8SDZ and then connect the SDP board to the USB port of the PC using the supplied cable. When the evaluation system is detected, proceed through any dialog boxes that appear to complete the installation.
Do not connect power to the hardware until both the EVAL-AD7124-4SDZ/EVAL-AD7124-8SDZ and SDP boards are connected via connector A. Figure below shows a functional block diagram of the test setup for the single and multiple thermistor configuration. The EVAL-AD7124-4SDZ/EVAL-AD7124-8SDZ evaluation board is required to test the circuit. In addition, the following sensor and resistors are required for proper operation:
To configure the hardware, take the following steps:
The AD7124_EVAL+ Software interfaces with the EVAL-AD7124-4SDZ/EVAL-AD7124-8SDZ and EVAL-SDP-CB1Z hardware. It can be used to connect to the hardware, configure the ADC, perform a calibrations and execute conversions to evaluate each Thermistor configuration (CN-0545) reference design.
Run the AD7124_EVAL+ Software, The evaluation software supports both the AD7124-4 and the AD7124-8 devices. On running the software, the user selects the evaluation board that is connected to the PC. For the AD7124-4, select EVAL-AD7124-4SDZ from the drop-down list, as shown in Figure below.
To configure the AD7124-4/AD7124-8 for Thermistor measurement, click the Thermistor demo mode button (see Figure above). Clicking the demo mode button configures the ADC software for Thermistor configurations. Additional instructions are provided regarding the thermistor configuration when the button is clicked.
One additional step is required before the AD7124-4/AD7124-8 is configured for Thermistor measurements: an internal full-scale and zero-scale calibration of the AD7124-4/AD7124-8. This calibration can be performed via the Register Map tab, as shown in below.
1. Click the ADC_Control register
2. Select Low Power mode
3. Internal full-scale calibration
4. Perform an internal zero-scale calibration.
5. When calibrations are complete, change the power mode to the required mode of operation, and ensure that the ADC is set to continuous conversion mode by selecting Continuous from the drop-down box in the *Mode* bit field of the ADC_Control register.
After calibrations, the board and device can now be configured for Thermistor measurements as discussed above.
Click the corresponding Thermistor demo mode and click SAMPLE to start gathering samples from the AD7124-4/AD7124-8. The Waveform tab and the Histogram tab show the data gathered from the AD7124-4/AD7124-8.