JAJSG89A January 2015 – September 2018 TPL5010
PRODUCTION DATA.
REXT is a theoretical value and may not be available in standard commercial resistor values. It is possible to closely approach the theoretical REXT using two or more standard values in parallel. However, standard values are characterized by a certain tolerance. This tolerance will affect the accuracy of the time interval.
The accuracy can be evaluated using the following procedure:
The example below illustrates the procedure.
From Table 3 REXT can be built with a parallel combination of two commercial values with 1% tolerance: R1 = 107 kΩ, R2 = 124 kΩ. The uncertainty of the equivalent parallel resistance can be found using Equation 4:
SPACER
The uncertainty of the parallel resistance is 0.82%, which means the value of REXT may range between REXT_MIN = 56.96 kΩ and REXT_MAX = 57.90 kΩ.
Using these value of REXT, the digitized timer intervals calculated by TADC equation mentioned in Equation 3 are respectively TADC_MIN = 586.85 s and TADC_MAX = 611.3 s, giving an error range of –1.88% / +2.19%. The asymmetry of the error range is due to the quadratic transfer function of the resistance digitizer.