26.3.9 Programming of Bias Current
The ADC uses a chip-level bias generator to provide bias current for its operation. The ADC's internal bias can be scaled by ADCBIA-
SPROG field of the ADCn_BIASPROG register. At lower conversion speeds, the ADCBIASPROG can be used to lower active power.
Some commonly used settings are given in the ADCBIASPROG register description. For proper operation, the ADC conversion speed
must be scaled accordingly. The scale factor is calculated as:
Bias scale factor = (1- ADCBIASPROG[2:0]/8) / (1+3∙ADCBIASPROG[3])
Figure 26.12. Bias Scale Factor
The bias programming register also includes the VFAULTCLR bit field. If VREFOF interrupt is enabled and it is triggered, then the user
needs to set this bit in the ISR before clearing the interrupt flag. This bit then needs to be reset after the interrupt flag is cleared in order
to enable the VREFOV flag to trigger on the next VREFOV condition.
The bias current settings should only be changed while the ADC is disabled (i.e. in NORMAL warm-up mode and no conversion in
progress).
26.3.10 Feature Set
The following sections explain different ADC features.
26.3.10.1 Conversion Tailgating
Scan conversions have priority over single channel conversions. This means that if scan and single triggers are received simultaneous-
ly, or even if the scan is received later when ADC is being warmed up for performing a single conversion, the scan conversion will have
priority and will be done before the single conversion. However, a scan trigger will not interrupt in the middle of a single conversion, i.e.,
if the single conversion is in the acquisition or approximation phase, then the scan will have to wait for the single conversion to com-
plete. If a scan sequence is triggered by a timer on a periodic basis, single channel conversion that started just before a scan trigger
can delay the start of the scan sequence, thus causing jitter in sample rate. To solve this, conversion tailgating can be chosen by setting
TAILGATE in ADCn_CTRL. When this bit is set, any triggered single channels will wait for the next scan sequence to finish before acti-
vating (see
Figure 26.13 ADC Conversion Tailgating on page 860
). The single channel will then follow immediately after the scan
sequence. In this way, the scan sequence will always start immediately when triggered, provided that the period between the scan trig-
gers is big enough to allow the single sample conversion that was triggered to finish before the next scan trigger arrives. Note that if
tailgating is set and a single channel conversion is triggered, it will indefinitely wait for a scan conversion before starting the single chan-
nel conversion.
SINGLESTART
SCANSTART
SCANACT
ADC action
SINGLEACT
Scan
Single
Scan
Single
Scan
Figure 26.13. ADC Conversion Tailgating
Reference Manual
ADC - Analog to Digital Converter
silabs.com
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