RM0367 Rev 7 325/1043
RM0367 Analog-to-digital converter (ADC)
352
14.6.2 Auto-off mode (AUTOFF)
The ADC has an automatic power management feature which is called auto-off mode, and
is enabled by setting AUTOFF = 1 in the ADC_CFGR1 register.
When AUTOFF = 1, the ADC is always powered off when not converting and automatically
wakes-up when a conversion is started (by software or hardware trigger). A startup-time is
automatically inserted between the trigger event which starts the conversion and the
sampling time of the ADC. The ADC is then automatically disabled once the sequence of
conversions is complete.
Auto-off mode can cause a dramatic reduction in the power consumption of applications
which need relatively few conversions or when conversion requests are timed far enough
apart (for example with a low frequency hardware trigger) to justify the extra power and
extra time used for switching the ADC on and off.
Auto-off mode can be combined with the wait mode conversion (WAIT = 1) for applications
clocked at low frequency. This combination can provide significant power savings if the ADC
is automatically powered-off during the wait phase and restarted as soon as the ADC_DR
register is read by the application (see Figure 48: Behavior with WAIT = 1, AUTOFF = 1).
Note: Please refer to the Section Reset and clock control (RCC) for the description of how to
manage the dedicated 14 MHz internal oscillator. The ADC interface can automatically
switch ON/OFF the 14 MHz internal oscillator to save power.
Figure 47. Behavior with WAIT = 0, AUTOFF = 1
1. EXTSEL = TRGx, EXTEN = 01 (rising edge), CONT = x, ADSTART = 1, CHSEL = 0xF, SCANDIR = 0, WAIT = 1,
AUTOFF = 1
For code example, refer to A.8.12: Auto off and no wait mode sequence code example.
MSv30345V2
TRGx
EOC
EOS
ADC_DR Read
access
ADC state
ADC_DR
by H/Wby S/W
triggered
D1 D3
D2
D4
RDY CH1 CH2
Startup CH4
CH3 OFF Startup
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