TPL5010_16 Datasheet, PDF (14/25 Pages) Texas Instruments – TPL5010 Nano-power System Timer with Watchdog Function

TPL5010
SNAS651 – JANUARY 2015
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• Required R_EXT, from Equation 1, R_EXT= 57.44kΩ.
From Table 3 R_EXT can be built with a parallel combination of two commercial values with 1% tolerance:
R1=107kΩ, R2=124kΩ. The uncertainty of the equivalent parallel resistance can be found using:
uR_//
R_//
¨§ ^uR1 ¸·²
© ^R1 ¹
¨§ ^uR2 ¸·²
© ^R2 ¹
(6)
Where uRn (n=1,2) represent the uncertainty of a resistance,
u_{R n}
RnTolerance
3
(7)
The uncertainty of the parallel resistance is 0.82%, meaning the value of R_EXT may range between R_{EXT_MIN} =
56.96 kΩ and R_{EXT_MAX} = 57.90 kΩ.
Using these value of R_EXT, the digitized timer intervals calculated with Equation 4 are respectively T_{ADC_MIN} =
586.85s and T_{ADC_MAX} = 611.3s, 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.
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