ZHCSJC0 January 2019 ADS1260-Q1 , ADS1261-Q1
ADVANCE INFORMATION for pre-production products; subject to change without notice.
The key considerations in the design of a 3-wire RTD circuit are the accuracy, stability and noise of the measurement, accuracy of the lead-wire compensation and self-heating of the sensor. Stability of the measurement is determined by the offset and gain drift of the ADC and by the drift of the external reference resistor. Measurement noise is determined by the ADC sample rate and by the digital filter settings. These parameters are not summarized here. Table 45 summarizes the basic design goals for a 3-wire Pt100 RTD.
DESIGN PARAMETER | VALUE |
---|---|
RTD sensor type | 3-wire Pt100 |
RTD resistance range | 20 Ω to 400 Ω |
RTD lead resistance range | 0 Ω to 10 Ω |
RTD self heating | < 1 mW |
Table 46 summarize the parameters of the detailed design procedure that follows.
DESIGN PARAMETER | DESIGN VALUE | |
---|---|---|
IIDAC | IDAC current | 500 µA |
PRTD | RTD power dissipation | 0.1 mW |
VRTD | RTD input voltage | 0.20 V |
Gain | ADC gain | 8 |
VREF | Reference voltage (design target allows for 10% overrange) | 1.76 V |
RREF | Reference resistor (senses the IDAC current to generate VREF) | 3.52 kΩ |
RBIAS | Bias resistor (provides the RTD level-shift voltage) | 1.10 kΩ |
VRTDN | RTD negative input voltage | 1.1 V |
VRTDP | RTD positive input voltage | 1.31 V |
VIDAC1 | IDAC1 loop voltage | 3.37 V |