ZHCSH80E September 2017 – May 2019 TMP235 , TMP236
PRODUCTION DATA.
See Figure 13 for suggested connections to an ADC input stage. Most CMOS-based ADCs have a sampled data comparator input structure. When the ADC charges the sampling capacitor (CSAMPLE), the capacitor requires instantaneous charge from the output of the analog source temperature sensor, such as the TMP23x. Therefore, the output impedance of the temperature sensor can affect ADC performance. In most cases, adding an external capacitor (CFILTER) mitigates design challenges. The TMP23x is specified and characterized with a 1000-pF maximum capacitive load (CLOAD). Figure 13 shows CLOAD as the sum of CFILTER + CMUX + CSAMPLE. TI recommends maximizing the CFILTER value while allowing for the maximum specified ADC input capacitance (CMUX + CSAMPLE) to limit the total CLOAD at 1000 pF. In most cases, a 680-pF CFILTER provides a reasonable allowance for ADC input capacitance to minimize ADC sampling error and reduce noise coupling. An optional series resistor (RFILTER) and CFILTER provides additional low-pass filtering to reject system level noise. TI recommends placing RFILTER and CFILTER as close as possible to the ADC input for optimal performance.