Si1000/1/2/3/4/5
5.7. Voltage and Ground Reference Options
The voltage reference MUX is configurable to use an externally connected voltage reference, one of two
internal voltage references, 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 97.
Electrical specifications are can be found in the Electrical Specifications Chapter.
Important Note About the V
and AGND Inputs: Port pins are used as the external V
and AGND
REF
REF
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 refer-
ence 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 207 for complete Port I/O configuration details. The exter-
nal reference voltage must be within the range 0 V
VDD_MCU and the external ground reference
REF
must be at the same DC voltage potential as GND.
REF0CN
ADC
Input
Mux
Temp Sensor
EN
REFOE
EN
Internal 1.68V
Reference
VDD
External
Voltage
Reference
Circuit
R1
P0.0/VREF
VDD/DC+
00
01
10
11
VREF
(to ADC)
Internal 1.8V
Regulated Digital Supply
GND
Internal 1.65V
High Speed Reference
+
4.7F
0.1F
GND
0
1
Ground
(to ADC)
Recommended
Bypass Capacitors
P0.1/AGND
REFGND
Figure 5.10. Voltage Reference Functional Block Diagram
5.8. External Voltage References
To use an external voltage reference, REFSL[1:0] should be set to 00 and the internal 1.68 V precision ref-
erence should be disabled by setting REFOE to 0. Bypass capacitors should be added as recommended
by the manufacturer of the external voltage reference.
Rev. 1.0
95
SILICON [ SILICON ]
