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Figure 28.2. ADC Conversion Timing
HFPERCLKADCn
Prescaled clock (4x)
ADC action
SINGLEAT/
SCANAT
Bit 11 Bit 10 Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
6-bit value ready 8-bit value ready
12-bit value ready
28.3.3 Warm-up Time
The ADC needs to be warmed up some time before a conversion can take place. This time period is
called the warm-up time. When enabling the ADC or changing references between samples, the ADC
is automatically warmed up for 1µs and an additional 5 µs if the bandgap is selected as reference.
Normally, the ADC will be warmed up only when samples are requested and is shut off when there are
no more samples waiting. However, if lower latency is needed, configuring the WARMUPMODE field in
ADCn_CTRL allows the ADC and/or reference to stay warm between samples, eliminating the need for
warm-up. Figure 28.3 (p. 684) shows the analog power consumption in scenarios using the different
WARMUPMODE settings.
Only the bandgap reference selected for scan mode can be kept warm. If a different bandgap reference
is selected for single mode, the warm-up time still applies.
• NORMAL: ADC and references are shut off when there are no samples waiting. a) in Figure 28.3 (p.
684) shows this mode used with an internal bandgap reference. Figure d) shows this mode when
using VDD or an external reference.
• FASTBG: Bandgap warm-up is eliminated, but with reduced reference accuracy. d) in Figure 28.3 (p.
684) shows this mode used with an internal bandgap reference.
• KEEPSCANREFWARM: The reference selected for scan mode is kept warm. The ADC will still need
to be warmed up before conversion. b) in Figure 28.3 (p. 684) shows this mode used with an internal
bandgap reference.
• KEEPADCWARM: The ADC and the reference selected for scan mode is kept warm. c) in
Figure 28.3 (p. 684) shows this mode used with an internal bandgap reference.
The minimum warm-up times are given in µs. The timing is done automatically by the ADC, given that
a proper time base is given in the TIMEBASE bits in ADCn_CTRL. The TIMEBASE must be set to the
number of HFPERCLK which corresponds to at least 1 µs. The TIMEBASE only affects the timing of the
warm-up sequence and not the ADC_CLK.
When entering Energy Modes 2 or 3, the ADC must be stopped and WARMUPMODE in ADCn_CTRL
written to 0.
2013-05-08 - Wonder Gecko Family - d0233_Rev0.50
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