Vrefdiv Sources; Supply Voltage Monitoring (Vsense); Input Range And Accuracy Settings - Silicon Laboratories EFR32xG21 Wireless Gecko Reference Manual

22.3.5 VREFDIV Sources

The ACMP has two internal bandgap references: 2.5 V and 1.25 V. In addition, AVDD can be used as a reference. To select one of
these references, configure POSSEL / NEGSEL to VREFDIVAVDD, VREFDIV1V25, or VREFDIV2V5. The ACMP also includes sam-
ple/hold functionality to reduce energy consumption. To enable the sample/hold feature, select VREFDIVAVDDLP, VREFDIV1V25LP,
or VREFDIV2V5LP. These references can be divided by configuring VREFDIV in ACMP_INPUTCTRL. This division factor will be
VREFDIV / 63, such that VREFOUT = VREFIN * (VREFDIV / 63).

22.3.6 Supply Voltage Monitoring (VSENSE)

The ACMP can be used to monitor supply voltages. This is done by selecting VSENSE01DIV4(LP) or VSENSE11DIV4(LP) for either
POSSEL or NEGSEL. Note that the input to the comparator core will be divided by 4, as illustrated in
page 604. To reduce energy consumption, a sample/hold circuit can be used to periodically sample the power supplies. To enable this,
select VSENSE01DIV4LP or VSENSE11DIV4LP in POSSEL / NEGSEL. Because the sample/hold feature uses the comparator in a
non-continuous fashion, enabling this will increase response times and reduce the accuracy of the comparator. The connections be-
tween VSENSE0 and VSENSE1 to power supplies are summarized in
ACMP instance
ACMP0
ACMP1

22.3.7 Input Range and Accuracy Settings

By default, the ACMP can accept external rail-to-rail inputs, from 0 to AVDD. If external voltages will never be higher than AVDD - 0.7
V, the INPUTRANGE bit in ACMP_CFG can be set to 1 to reduce the power consumption of the block.
The ACMP also has an adjustable accuracy setting (ACCURACY in ACMP_CFG). ACCURACY is set to LOW by default, which con-
serves power, but may have degraded performance for rapidly changing analog Port selections in either the ACMP or the GPIO. AC-
CURACY can be set to HIGH to insure ACMP accuracy (at the expense of extra power consumption), when configuration changes are
expected at a high rate (more than once per ms, for example), such as when scanning through channels or using the capacitive sense
feature.
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Table 22.2 VSENSE connections on page
Table 22.2. VSENSE connections
VSENSE0
AVDD
DVDD
Reference Manual
ACMP - Analog Comparator
Figure 22.1 ACMP Overview on
606.
VSENSE1
VDDIO0
Not connected
Rev. 0.4 | 606