Warmup Time And Initial Conversion; Analog Output; Output Mode - Silicon Laboratories EFR32xG14 Wireless Gecko Reference Manual

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23.3.6 Warmup Time and Initial Conversion

When a channel is first enabled it needs to warm up. This is performed automatically during the first conversion. The time required to
warm up depends on the programmed DRIVESTRENGTH field in VDACn_OPAx_CTRL. In
758 the minimum WARMUPTIME field for each drive strength is specified. Software is responsible for programming the correct value
to WARMUPTIME before enabling a channel. If the time is programmed too short, an undefined voltage may be output until the VDAC
settles.
The CHxWARM bits in VDACn_STATUS are set when the warmup period has completed.
A consequence of the warmup period is that in continuous mode, the first conversion might take longer than the following conversions.
In order to make sure all samples have the same timing, perform a dummy conversion to make the VDAC settle to a known voltage
first.
DRIVESTRENGTH
0
1
2
3

23.3.7 Analog Output

The output selection for each VDAC channel is configured in the VDACn_OPAx_OUT registers. Each VDAC channel has its own main
output pin, VDACn_OUTx, that can be enabled with MAINOUTEN. In addition, several alternate outputs can be selected. These are
enabled by first setting ALTOUTEN and then setting the corresponding bit(s) in ALTOUTPADEN. The VDAC output can also be routed
to APORT by setting APORTOUTEN and configuring the APORTOUTSEL field to select the desired APORT.
The VDAC outputs also have direct internal connections to ADCs and ACMPs. These outputs are always enabled and can be selected
by configuring the input selection for the ADC/ACMP.
In sample/off mode the VDAC will only drive the output for the duration programmed in SETTLETIME (in VDACn_OPAx_TIMER regis-
ter) for each incoming conversion trigger. In continuous mode the VDAC will continue to drive the output until the channel is disabled.
However, note that also in this mode a conversion trigger is needed before the output is enabled. See
Channel and 23.3.4.3 Conversion

23.3.8 Output Mode

The two VDAC channels can act as two separate single ended channels or be combined into one differential channel. This is selected
through the DIFF bit in VDACn_CTRL.
23.3.8.1 Single Ended Output
When operating in single ended mode, the channel 0 output is on VDACn_OUT0 and the channel 1 output is on VDACn_OUT1. The
output voltage can be calculated using
where CHxDATA is a 12-bit unsigned integer.
23.3.8.2 Differential Output
When operating in differential mode, both VDAC outputs are used. The differential conversion uses VDACn_CH0DATA as source. The
positive output is on VDACn_OUT1 and the negative output is on VDACn_OUT0. Since the output can be negative, it is expected that
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Table 23.2. VDAC Warmup Time
Trigger.
Figure 23.2 VDAC Single Ended Output Voltage on page 758
V = V
OUT VDACn_OUTx
Figure 23.2. VDAC Single Ended Output Voltage
WARMUPTIME
100 µs
85 µs
8 µs
8 µs
- V = V x CHxDATA/4095
SS ref
Reference Manual
VDAC - Digital to Analog Converter
Table 23.2 VDAC Warmup Time on page
23.3.3 Enabling and Disabling a
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