C8051F960-B-GM Datasheet, PDF (101/492 Pages) Silicon Laboratories – Ultra Low Power 128K, LCD MCU Family

C8051F96x
5.10. External Voltage Reference
To use an external voltage reference, REFSL[1:0] should be set to 00. Bypass capacitors should be added
as recommended by the manufacturer of the external voltage reference. If the manufacturer does not pro-
vide recommendations, a 4.7uF in parallel with a 0.1uF capacitor is recommended.
5.11. Internal Voltage Reference
For applications requiring the maximum number of port I/O pins, or very short VREF turn-on time, the
1.65 V high-speed reference will be the best internal reference option to choose. The high speed internal
reference is selected by setting REFSL[1:0] to 11. When selected, the high speed internal reference will be
automatically enabled/disabled on an as-needed basis by ADC0.
For applications with a non-varying power supply voltage, using the power supply as the voltage reference
can provide ADC0 with added dynamic range at the cost of reduced power supply noise rejection. To use
the 1.8 to 3.6 V power supply voltage (V_DD) or the 1.8 V regulated digital supply voltage as the reference
source, REFSL[1:0] should be set to 01 or 10, respectively.
5.12. Analog Ground Reference
To prevent ground noise generated by switching digital logic from affecting sensitive analog measure-
ments, a separate analog ground reference option is available. When enabled, the ground reference for
ADC0 during both the tracking/sampling and the conversion periods is taken from the P0.1/AGND pin. Any
external sensors sampled by ADC0 should be referenced to the P0.1/AGND pin. This pin should be con-
nected to the ground terminal of any external sensors sampled by ADC0. If an external voltage reference is
used, the P0.1/AGND pin should be connected to the ground of the external reference and its associated
decoupling capacitor. The separate analog ground reference option is enabled by setting REFGND to 1.
Note that when sampling the internal temperature sensor, the internal chip ground is always used for the
sampling operation, regardless of the setting of the REFGND bit. Similarly, whenever the internal 1.65 V
high-speed reference is selected, the internal chip ground is always used during the conversion period,
regardless of the setting of the REFGND bit.
5.13. Temperature Sensor Enable
The TEMPE bit in register REF0CN enables/disables the temperature sensor. While disabled, the tem-
perature sensor defaults to a high impedance state and any ADC0 measurements performed on the sen-
sor result in meaningless data. See Section “5.8. Temperature Sensor” on page 97 for details on
temperature sensor characteristics when it is enabled.
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