25.3.5 Input Pin Considerations
For external ACMP inputs routed through the APORT, the maximum supported analog input voltage will be limited to the
MIN(V
ACMPVDD
, IOVDD) (where V
ACMPVDD
is selected by the PWRSEL bitfield in ACMPn_CTRL). Note that pins configured as ACMP
inputs should disable OVT (by setting the corresponding GPIO_Px_OVTDIS bit) to reduce any potential distortion introduced by the
OVT circuitry.
25.3.6 Input Selection
The POSSEL and NEGSEL fields in ACMPn_INPUTSEL control the input connections to the positive and negative inputs of the compa-
rator. The user can select external GPIO pins on the chip, or select a number of internal chip voltages. Pins are selected by configuring
channels on APORT buses. Not all selectable channels are available on a given device, as different devices within a family may not
implement or bring out all of the I/O defined for that family. Refer to the data sheet for channel availability and pin mapping.
There are limitations on the POSSEL and NEGSEL connections that can be made. The user cannot select an X-bus for both POSSEL
and NEGSEL simultaneously, nor a Y-bus for both POSSEL and NEGSEL simultaneously. The second limitation is that when using the
feedback resistor only X-bus selections can be made for POSSEL. (The resistor only physically exists on the positive input of the com-
parator).
The user may also select from a number of internal voltages. VADIV and VBDIV are two dividable voltages. VADIV can be V
ACMPVDD
divided, or the user can choose to select inputs from a number of APORT buses. VBDIV consists of two dividable band-gap references
of either 1.25V or 2.5V. Each of these voltages have dividers in the ACMPn_HYSTERESIS0/1 registers. The formula for the division of
these voltages is:
VADIV = VA ∙ ( (DIVVA+1) / 64 )
Figure 25.3. VA Voltage Division
VBDIV = VB ∙ ( (DIVVB+1) / 64 )
Figure 25.4. VB Voltage Division
Either VADIV and VBDIV can also be used as an input to a lower power reference: VLP. Which of the two is used is configured via the
VLPSEL field in ACMPn_INPUTSEL. If the user selects VLP as an input source, then VADIV or VBDIV cannot be used as the source
for the other input.
The POSSEL and NEGSEL fields also allow input from the on-chip VDAC channel 0 or VDAC channel 1.
ACMP can be configured to operate with a selected level of accuracy depending on the setting of ACCURACY in ACMPn_CTRL. The
default is low-accuracy mode where ACMP operates with lower accuracy but consumes less current. When higher accuracy is needed
the user can set ACCURACY=1 at the cost of higher current consumption.
Reference Manual
ACMP - Analog Comparator
silabs.com
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