10.3.5.3.2 Low Noise (LN) Discontinuous Conduction Mode (DCM)
To enable DCM, the LNFORCECCM bit in EMU_DCDCMISCCTRL must be cleared before entering LN. Typically, this configuration
would occur while the part was in Bypass mode. Once DCM is enabled, the DC-DC should operate in DCM at light load currents. How-
ever, as the load current increases, the DC-DC will automatically transition into CCM without software intervention.
The advantage of DCM is improved efficiency for light load currents. However, in DCM the DC-DC has poorer dynamic response to
changes in load current, leading to potentially larger changes in the regulated output voltage. In addition, DCM increases the potential
RF switching interference, because in DCM the DC-DC switching events are load dependent and can no longer be synchronized with
radio operation. For these reasons, DCM is not recommended for radio applications or for non-radio applications that expect large in-
stantaneous load current steps. For example, if the DC-DC is in DCM, firmware may need to increment the core clock frequency in
small steps to prevent a large sudden load increase.
In DCM, the recommended DC-DC converter switching frequency is 3 MHz (RCOBAND = 0).
10.3.5.4 DC-to-DC Programming Guidelines
Note:
Refer to Application Note
AN0948: EFM32 and EFR32 Series 1 Power Configurations and DC-DC
for detailed information on pro-
gramming the DC-DC. Application Notes can be found on the Silicon Labs website (www.silabs.com/32bit-appnotes) or using the [
Ap-
plication Notes
] tile in Simplicity Studio.
10.3.6 Analog Peripheral Power Selection
The analog peripherals (e.g., ULFRCO, LFRCO, LFXO, HFRCO, AUXHFRCO, VMON, IDAC, ADC) are powered from an internal ana-
log supply domain, VDDX_ANA. VDDX_ANA may be supplied from either the AVDD or DVDD supply pins, depending on the configura-
tion of the ANASW bit in the EMU_PWRCTRL register. Changes to the ANASW setting should be made immediately out of reset (i.e.,
in the Unconfigured Configuration), before all clocks (with the exception of HFRCO and ULFRCO) are enabled. If the DCDC converter
is used and ANASW is set to 1, the switch will not take effect until after the DCDC output voltage has reached its target level. To pre-
vent supply transients, firmware should configure and enable the DCDC, configure ANASW, and then enable clocks. If the DCDC con-
verter is not used, IMMEDIATEPWRSWITCH should be set prior to setting ANASW so hardware can immediately apply the switch with-
out waiting for the DCDC to settle.
Once ANASW is configured it should not be changed. Note that the flash is always powered from the AVDD pin, regardless of the state
of the ANASW bit.
Table 10.4. Analog Peripheral Power Configuration
ANASW
Analog Peripheral Power Supply
Source (VDDX_ANA)
Comments
0 (default)
AVDD pin
This configuration may provide a quieter supply to the analog
modules, but is less efficient as AVDD is typically at a higher
voltage than DVDD.
1
DVDD pin
This configuration may provide a noisier supply to the analog
modules, but is more efficient. However, because the maximum
allowable input voltage to many of the analog modules using
APORT is limited to MIN(VDDX_ANA,IOVDD), this setting could
artificially limit your analog input range.
Reference Manual
EMU - Energy Management Unit
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