Honeywell CC-TDI110 Digital Input IOTA No. 51308394-175 Rev E1 CSQ Made in USA

 
 
 
SIMILAR PRODUCTS
 

 
As shown in Figure 5, the excitation current sources must flow out the AIN6 and AIN7 pins and therefore through the input filter before reaching the thermistor. Therefore, the input resistors will be set to 249 Ω to keep the voltage drop across them less than 0.25 V. This will prevent the voltage drop across them from interfering with the input common-mode limitations or the IDAC compliance. For the IDACs to remain operational, the inputs of the ADS1248 must satisfy the IDAC compliance voltage of 0.7V as specified in the product datasheet. Therefore the maximum voltages that can occur at the AIN6 and AIN7 inputs is calculated in Equation ( 18 ). The voltage at AIN6 is equal to the sum of VREF, VIN_MAX and the voltage drop across the input filter as shown in Equation (19). This voltage must remain less than the compliance voltage of 4.3V. The maximum reference voltage can therefore be calculated as shown in Equation ( 19 ).
 
 
Instrumentation amplifiers are the appropriate choice to buffer the analog input module due to their high input impedance. DC errors from the INA will directly contribute to the final accuracy, therefore an instrumentation amplifier with low offset voltage (VOS), low VOS drift (VOS(DRIFT)), low gain error and gain nonlinearity, high common-mode rejection ratio (CMRR), and high power-supply rejection ratio (PSRR) will help keep the error contribution of the amplifier as low as possible. The INA826 was chosen because it achieves 240uV typical, VOS and 2.4 uV/°C typical, VOS(DRIFT) , +/-0.003% typical gain error and 1ppm typical gain nonlinearity. It also features a typical CMRR of 95 dB and a typical PSRR of 124dB. Wide input and output voltage ranges are also required in this application. INA826 has a wide supply range from 2.7V to 36V and rail- to -rail output stage which makes it suitable in this design.
 
 
 
The difference amplifier is added to attenuate the input signal into a proper input range of the ADC. The on-chip resistors are laser-trimmed for accurate gain and high common-mode rejection. For ADS1248, the input range is +/-VREF/GAIN. For gain =1, the maximum input range is +/-2.5V. The maximum input voltage for this design is +/-10v, so a gain of 0.25 maximum is required. INA159 is a fixed gain of 0.2 with +/- 100uV typical, VOS and +/-0.002% typical, VOS(DRIFT) , +/-0.005% typical gain error and +/-0.0002%FS typical gain nonlinearity which makes it an appropriate choice. It also features a typical CMRR of 96dB.