C8051F120DK Silicon Laboratories Inc, C8051F120DK Datasheet - Page 59

• Manufacturer Part Number: C8051F120DK
• Description: DEVKIT-F120/21/22/23/24/25/26/27
• Manufacturer: Silicon Laboratories Inc
• Type: MCUr

Specifications of C8051F120DK

• Contents: Evaluation Board, Power Supply, USB Cables, Adapter and Documentation
• Processor To Be Evaluated: C8051F12x and C8051F13x
• Interface Type: USB
• Silicon Manufacturer: Silicon Labs
• Core Architecture: 8051
• Silicon Core Number: C8051F120
• Silicon Family Name: C8051F12x
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: C8051F120, 121, 122, 123, 124, 125, 126, 127
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 336-1224

5.2.3. 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 5.4 shows the equivalent ADC0 input circuits
for both Differential and Single-ended modes. Notice that the equivalent time constant for both input cir-
cuits 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
minimum settling time of 1.5 µs is required after any MUX or PGA selection. Note that in low-power track-
ing 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.
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).
TOTAL
AIN0.x
AIN0.y
is the sum of the ADC0 MUX resistance and any external source resistance.
RC
Differential Mode
MUX Select
MUX Select
Input
= R
MUX
R
R
* C
Equation 5.1. ADC0 Settling Time Requirements
MUX
MUX
SAMPLE
= 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
C8051F120/1/2/3/4/5/6/7
C
AIN0.x
SAMPLE
Single-Ended Mode
TOTAL
RC
MUX Select
Input
C8051F130/1/2/3
= R
reduces to R
MUX
R
* C
MUX
SAMPLE
= 5k
MUX
C
. An absolute
SAMPLE
= 10pF
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