C8051F045 View Datasheet(PDF) - Silicon Laboratories
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C8051F045 Datasheet PDF : 328 Pages
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C8051F040/1/2/3/4/5/6/7
5.3.3. Settling Time Requirements
A minimum tracking time is required before an accurate conversion can be performed. This tracking time is
determined by the ADC0 MUX resistance, the ADC0 sampling capacitance, any external source resis-
tance, and the accuracy required for the conversion. Figure 5.5 shows the equivalent ADC0 input circuits
for both differential and Single-ended modes. Notice that the equivalent time constant for both input circuits
is the same. The required settling time for a given settling accuracy (SA) may be approximated by
Equation 5.2. When measuring the Temperature Sensor output, RTOTAL reduces to RMUX. Note that in
Low-Power tracking mode, three SAR clocks are used for tracking at the start of every conversion. For
most applications, these three SAR clocks will meet the tracking requirements. See Table 5.2 for absolute
minimum settling/tracking time requirements.
t
=
ln
S-2---An--
RTOTALCSAMPLE
Equation 5.2. ADC0 Settling Time Requirements
Where:
SA is the settling accuracy, given as a fraction of an LSB (for example, 0.25 to settle within 1/4 LSB)
t is the required settling time in seconds
RTOTAL is the sum of the ADC0 MUX resistance and any external source resistance.
n is the ADC resolution in bits (12).
Differential Mode
Single-Ended Mode
MUX Select
MUX Select
AIN0.x
RMUX = 5k
CSAMPLE = 10pF
AIN0.x
RMUX = 5k
RCInput= RMUX * CSAMPLE
RCInput= RMUX * CSAMPLE
CSAMPLE = 10pF
AIN0.y
RMUX = 5k
MUX Select
Figure 5.5. ADC0 Equivalent Input Circuits
CSAMPLE = 10pF
56
Rev. 1.5
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