Si1000/1/2/3/4/5
0.68 uH
1 uF
DC-DC Converter
Enabled
4.7 uF
0.9 to 1.8 V
Supply Voltage
GND_MCU/
VBAT GND/VBAT- DCEN
DC-
VDD_MCU/
DC+
(one-cell mode)
VBAT GND/VBAT- DCEN
GND_MCU/
DC-
DC-DC Converter
Disabled
VDD_MCU/
DC+
1.8 to 3.6 V
Supply Voltage
(two-cell mode)
Figure 16.2. DC-DC Converter Configuration Options
When the dc-dc converter “Enabled” configuration (one-cell mode) is chosen, the following guidelines
apply:
In most cases, the GND/VBAT– pin should not be externally connected to GND.
The 0.68 µH inductor should be placed as close as possible to the DCEN pin for maximum efficiency.
The 4.7 µF capacitor should be placed as close as possible to the inductor.
The current loop including GND/VBAT-, the 4.7 µF capacitor, the 0.68 µH inductor and the DCEN pin
should be made as short as possible to minimize capacitance.
The PCB traces connecting VDD_MCU/DC+ to the output capacitor and the output capacitor to
GND_MCU/DC– should be as short and as thick as possible in order to minimize parasitic inductance.
16.5. Minimizing Power Supply Noise
To minimize noise on the power supply lines, the GND/VBAT- and GND_MCU/DC- pins should be kept
separate, as shown in Figure 16.2; GND_MCU/DC- should be connected to the pc board ground plane.
The large decoupling capacitors in the input and output circuits ensure that each supply is relatively quiet
with respect to its own ground. However, connecting a circuit element "diagonally" (e.g., connecting an
external chip between VDD_MCU/DC+ and GND/VBAT-, or between VBAT and GND_MCU/DC-) can
result in high supply noise across that circuit element.
To accommodate situations in which ADC0 is sampling a signal that is referenced to one of the external
grounds, we recommend using the Analog Ground Reference (P0.1/AGND) option described in Section
5.12. This option prevents any voltage differences between the internal chip ground and the external
grounds from modulating the ADC input signal. If this option is enabled, the P0.1 pin should be tied to the
168
Rev. 1.0
SILICON [ SILICON ]
