C8051F34A-GMR Silicon Labs, C8051F34A-GMR Datasheet - Page 47

• Manufacturer Part Number: C8051F34A-GMR
• Description: 8-bit Microcontrollers - MCU 48 MIPS 64KB 10ADC
• Manufacturer: Silicon Labs

Specifications of C8051F34A-GMR

• Rohs: yes
• Core: 8051
• Processor Series: C8051
• Data Bus Width: 8 bit

5.3.3. Settling Time Requirements
When the ADC0 input configuration is changed (i.e., a different AMUX0 selection is made), a minimum
tracking time is required before an accurate conversion can be performed. This tracking time is determined
by the AMUX0 resistance, the ADC0 sampling capacitance, any external source resistance, and the accu-
racy required for the conversion. 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 mini-
mum tracking time requirements.
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 ADC0 settling time for a
given settling accuracy (SA) may be approximated by Equation 5.1. When measuring the Temperature
Sensor output or
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
R
n is the ADC resolution in bits (10).
TOTAL
is the sum of the AMUX0 resistance and any external source resistance.
Px.x
Px.x
RC
V
Differential Mode
MUX Select
Input
DD with respect to GND, R
Select
MUX
= R
Equation 5.1. ADC0 Settling Time Requirements
MUX
R
R
* C
Figure 5.5. ADC0 Equivalent Input Circuits
MUX
MUX
SAMPLE
= 5k
= 5k
C8051F340/1/2/3/4/5/6/7/8/9/A/B/C/D
t
=
C
C
ln
SAMPLE
SAMPLE


------ -
SA
2
= 5pF
= 5pF
n


TOTAL

Rev. 1.3
R
TOTAL
reduces to R
C
Px.x
SAMPLE
Single-Ended Mode
RC
MUX Select
MUX
Input
= R
. See Table 5.1 for ADC0 minimum
MUX
R
* C
MUX
SAMPLE
= 5k
C
SAMPLE
= 5pF
47