C8051F980-C-GM Datasheet, PDF (88/325 Pages) Silicon Laboratories – Ultra Low Power, 8-2 kB Flash, Capacitive Sensing MCU

C8051F99x-C8051F98x
5.9. Voltage and Ground Reference Options
The voltage reference MUX is configurable to use an externally connected voltage reference, the internal
voltage reference, or one of two power supply voltages (see Figure 5.10). The ground reference MUX
allows the ground reference for ADC0 to be selected between the ground pin (GND) or a port pin
dedicated to analog ground (P0.1/AGND).
The voltage and ground reference options are configured using the REF0CN SFR described on page 90.
Electrical specifications are can be found in the Electrical Specifications Chapter.
Important Note About the V_REF and AGND Inputs: Port pins are used as the external V_REF and AGND
inputs. When using an external voltage reference or the internal precision reference, P0.0/VREF should be
configured as an analog input and skipped by the Digital Crossbar. When using AGND as the ground
reference to ADC0, P0.1/AGND should be configured as an analog input and skipped by the Digital
Crossbar. Refer to Section “21. Port Input/Output” on page 215 for complete Port I/O configuration details.
The external reference voltage must be within the range 0  V_REF  VDD and the external ground
reference must be at the same DC voltage potential as GND.
REF0CN
Temp Sensor
EN
ADC
Input
Mux
VDD
R1
External
V o lta g e
Reference
C irc u it
P 0 .0 /V R E F
VDD
GND
+
4.7F
0.1F
GND
Recommended
Bypass Capacitors
P 0.1 /A G N D
00
01
Internal 1.8V
10
Regulated Digital Supply
11
Internal 1.65V
High Speed Reference
0
1
REFGND
Figure 5.10. Voltage Reference Functional Block Diagram
VREF
(to ADC)
G round
(to ADC)
88
Rev. 1.2