10.3.4.3 Power Configuration 2: DC-DC
For the lowest power applications, the DC-DC converter can be used to power the DVDD supply, as well as RFVDD and PAVDD.
In Power Configuration 2, the DC-DC Output (V
DCDC
) is connected to DVDD. DVDD powers the internal Digital LDO (i.e., RE-
GPWRSEL=1) which powers the digital circuits. AVDD is connected to the main supply voltage. The internal analog blocks may be
powered from AVDD or DVDD, depending on the ANASW configuration. RFVDD and PAVDD are powered from V
DCDC
as well.
IOVDD could be connected to either the main supply (as shown below) or to V
DCDC
, depending on the system IO requirements. Be-
cause V
DCDC
will be unpowered (i.e., floating) at startup, if IOVDD is powered from the DC-DC converter then any circuit attached to
IOVDD will not be powered until the DC-DC is configured (or the bypass switch is enabled). Refer to
section
for further details and issues that may result when connecting IOVDD to V
DCDC
.
DECOUPLE
DVDD
AVDD
VREGSW
Main
Supply
VREGVSS
IOVDD
VREGVDD
+
–
V
DD
DC-DC
DC-DC
Driver
Bypass
Switch
OFF
FLASH
DECOUPLE
DVDD
AVDD
VREGSW
VREGVSS
IOVDD
VREGVDD
ANASW
0
1
REGPWRSEL
0
1
Digital
Logic
PAVDD
RFVDD
RF
Analog
V
DCDC
Analog
Blocks
Digital
LDO
RF
Power
Amplifier
Figure 10.4. DC-DC Standard Power Configuration
As the Main Supply voltage approaches the DC-DC output voltage, it eventually reaches a point where becomes inefficient (or impossi-
ble) for the DC-DC module to regulate V
DCDC
. At this point, firmware can enable bypass mode, which effectively disables the DC-DC
and shorts the Main Supply voltage directly to the DC-DC output. If and when sufficient voltage margin on the Main Supply returns, the
system can be switched back into DC-DC regulation mode.
An alternate "High RF Power" DC-DC configuration has the external Main Supply connected directly to the PAVDD. This configuration
supports a higher transmit power (e.g., >13 dBm) required for some radio protocol specifications. No additional software setting is re-
quired for this mode. The following diagram shows an example of connecting PAVDD to the Main Supply while DVDD and RFVDD are
connected to the filtered V
DCDC
.
Reference Manual
EMU - Energy Management Unit
silabs.com
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