Analog front end (AFE) for sensing temperature in smart grid applications using RTD reference design

This reference design enables up to 4 Resistor Temperature Detectors (RTD) to be connected through one ADC in manner such that the solution is both compact and modular. Communication from the ADC to the processor is though an SPI interface. If 8 RTDs are required for an application, simply connect up one more of these modules. This solution is flexible to where it can handle 2 wire, 3 wire or 4 wire type RTDs.

Features
• Based on the ADS1248 24-Bit Delta-Sigma (ΔΣ) ADC With Internal PGA and Selectable Gain up to 128
• Can Measure 2-, 3-, or 4-Wire RTD Inputs
• Multiplexer (Analog Switch) to Switch Excitation Currents for Four RTD Inputs
• Uses Ratiometric Measurement for Higher Accuracy
• Accuracy • I2C I/O Expander for ADC Interface Control and Excitation Current Switching Provided (No External I/Os  Required)

Parts Include:

ADS1148    16-Bit Analog-to-Digital Converter For Temperature Sensors 
ADS1248    Precision 24 Bit ADC with integrated Low Noise PGA (48nV at a Gain of 128) 
CSD17571Q2  30V N-Channel NexFET Power MOSFETs, CSD17571Q2
TCA6408A  Low-Voltage 8-Bit I2C and SMBus I/O Expander 
TPS7A1633  60V, 5μA IQ Low-Dropout 100mA Linear Regulator with Enable and Power Good
TS3A5017  14-Ohm Dual SP4T Analog Switch 3.3-V/2.5-V Analog Multiplexer/Demultiplexer

Learn more by downloading the reference design below