C8051F020-TB Silicon Laboratories Inc, C8051F020-TB Datasheet - Page 46

• Manufacturer Part Number: C8051F020-TB
• Description: BOARD PROTOTYPING W/C8051F020
• Manufacturer: Silicon Laboratories Inc
• Type: MCUr

Specifications of C8051F020-TB

• Contents: Board
• Processor To Be Evaluated: C8051F02x
• Interface Type: USB
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: C8051F020
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

C8051F020/1
5.2.3. Settling Time Requirements
When the ADC0 input configuration is changed (i.e., a different MUX or PGA selection is made), a minimum settling
(or tracking) time is required before an accurate conversion can be performed. This settling time is determined by the
ADC0 MUX resistance, the ADC0 sampling capacitance, any external source resistance, and the accuracy required
for the conversion. Figure 5.4 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 5.1. When measuring the Temperature Sensor output,
R
every conversion. For most applications, these three SAR clocks will meet the tracking requirements. See Table 5.1
on page 58 for absolute minimum settling/tracking 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
R
n is the ADC resolution in bits (12).
46
TOTAL
TOTAL
AIN0.x
AIN0.y
reduces to R
is the sum of the ADC0 MUX resistance and any external source resistance.
RC
Differential Mode
MUX Select
MUX Select
Input
= R
MUX
MUX
R
R
* C
. Note that in low-power tracking mode, three SAR clocks are used for tracking at the start of
MUX
MUX
SAMPLE
Equation 5.1. ADC0 Settling Time Requirements
= 5k
= 5k
Figure 5.4. ADC0 Equivalent Input Circuits
t
C
C
SAMPLE
SAMPLE
=
ln
= 10pF
= 10pF


------ -
SA
2
n


Rev. 1.4

R
TOTAL
AIN0.x
C
SAMPLE
Single-Ended Mode
RC
MUX Select
Input
= R
MUX
R
* C
MUX
SAMPLE
= 5k
C
SAMPLE
= 10pF