Si1000/1/2/3/4/5
16. On-Chip DC-DC Converter (DC0)
Si1004/5 devices include an on-chip dc-dc converter to allow operation from a single cell battery with a
supply voltage as low as 0.9 V. The dc-dc converter is a switching boost converter with an input voltage
range of 0.9 to 1.8 V and a programmable output voltage range of 1.8 to 3.3 V. The default output voltage
is 1.9 V. The dc-dc converter can supply the system with up to 65 mW of regulated power (or up to
100 mW in some applications) and can be used for powering other devices in the system. This allows the
most flexibility when interfacing to sensors and other analog signals which typically require a higher supply
voltage than a single-cell battery can provide.
Figure 16.1 shows a block diagram of the dc-dc converter. During normal operation in the first half of the
switching cycle, the Duty Cycle Control switch is closed and the Diode Bypass switch is open. Since the
output voltage is higher than the voltage at the DCEN pin, no current flows through the diode and the load
is powered from the output capacitor. During this stage, the DCEN pin is connected to ground through the
Duty Cycle Control switch, generating a positive voltage across the inductor and forcing its current to ramp
up.
In the second half of the switching cycle, the Duty Cycle control switch is opened and the Diode Bypass
switch is closed. This connects DCEN directly to VDD_MCU/DC+ and forces the inductor current to charge
the output capacitor. Once the inductor transfers its stored energy to the output capacitor, the Duty Cycle
Control switch is closed, the Diode Bypass switch is opened, and the cycle repeats.
The dc-dc converter has a built in voltage reference and oscillator, and will automatically limit or turn off the
switching activity in case the peak inductor current rises beyond a safe limit or the output voltage rises
above the programmed target value. This allows the dc-dc converter output to be safely overdriven by a
secondary power source (when available) in order to preserve battery life. The dc-dc converter’s settings
can be modified using SFR registers which provide the ability to change the target output voltage, oscillator
frequency or source, Diode Bypass switch resistance, peak inductor current, and minimum duty cycle.
DC/DC Converter
VBAT
VDD_MCU/DC+
0.68 uH
DCEN
Diode
4.7 uF
Bypass
Duty
Cycle
Control
Control Logic
Voltage
Iload
Cload
1uF
DC0CN
Reference
DC/DC
Oscillator
DC0CF
Lparasitic
Lparasitic
GND/VBAT-
GND_MCU/DC-
Figure 16.1. DC-DC Converter Block Diagram
Rev. 1.0
165
SILICON [ SILICON ]
