SI9161 Datasheet, PDF (8/12 Pages) Vishay Siliconix – Optimized-Efficiency Controller for RF Power Amplifier Boost Converter

Si9161
Vishay Siliconix
OPERATION OF THE Si9161 BOOST CONVERTER
The Si9161 combined with optimized complementary
MOSFETs provides the ideal solution to small, high efficiency,
synchronous boost power conversion. Optimized for a 1-cell
lithium ion, or 3-cell to 4-cell Nickel metal hydride battery, it is
capable of switching at frequencies of up to 2 MHz. Combined
with the Si6801, a complimentary high-frequency MOSFET,
efficiencies of over 90% are easily achieved in a very small
area; with light-load mode, efficiency over 80% can be
achieved at power less than 1/2 W.
PWM Controller
The Si9161 implements a user-selectable synchronous/non-
synchronous voltage mode PWM control topology and is
especially designed for battery power conversion. Voltage-
mode control results in the most efficient power conversion
solution. Figure 1 below illustrates a schematic for a
synchronous boost converter with an input range of 2.7 V to
5 V which covers the range of 1-cell LiIon and 3-cell or 4-cell
NiMH/NiCd battery input respectively, and an output voltage of
5 V. Note the maximum input voltage is limited to the output
voltage for a boost converter.
The switching frequency is determined by an external
capacitor and resistor connected to C_osc and R_osc pins. The
graph on page 5 in the Typical Characteristics section shows
the typical C_osc and R_osc values for various switching
frequency. Si9161 oscillator frequency can be easily
synchronized to external frequency as long as external
switching frequency is higher than the internal oscillator
frequency. The synchronization circuit is a series resistor and
capacitor fed into the C_osc pin of the Si9161. The
synchronization pulse should be greater than 1.5 V in
amplitude and a near square wave pulsed clock. Figure 1
shows typical values for the synchronization components.
S-60752—Rev. B, 05-Apr-99
8
FIGURE 1. Si9161 Boost Converter
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