C8051F040-TB Silicon Laboratories Inc, C8051F040-TB Datasheet - Page 56

• Manufacturer Part Number: C8051F040-TB
• Description: BOARD PROTOTYPING W/C8051F040
• Manufacturer: Silicon Laboratories Inc
• Type: MCUr

Specifications of C8051F040-TB

• Contents: Board
• Processor To Be Evaluated: C8051F04x
• Interface Type: USB
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: C8051F040
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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, R
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.
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).
56
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
Equation 5.2. ADC0 Settling Time Requirements
* C
MUX
MUX
SAMPLE
= 5k
= 5k
Figure 5.5. ADC0 Equivalent Input Circuits
t
C
C
SAMPLE
SAMPLE
=
ln
= 10pF
= 10pF


------ -
SA
2
n



Rev. 1.5
R
TOTAL
C
AIN0.x
SAMPLE
Single-Ended Mode
RC
TOTAL
MUX Select
Input
= R
reduces to R
MUX
R
* C
MUX
SAMPLE
= 5k
MUX
C
. Note that in
SAMPLE
= 10pF