SC600
POWER MANAGEMENT
Applications Information
Regulated Fractional Charge Pump Operation
A fractional charge pump is a voltage converter which
implements switched capacitor techniques to produce an
output voltage that is one of several multiples of the input
voltage. Regulated fractional charge pumps (also called
charge pump regulators) use a linear regulator with vari-
ous charge pump configurations to deliver a regulated out-
put over a wide input voltage range. Regulated fractional
charge pumps have improved efficiency over ordinary lin-
ear regulator and charge pump circuit combinations. The
improved efficiency is achieved by implementing multiple
charge pump configurations on one integrated circuit.
The correct charge pump configuration is automatically
selected to meet the regulation requirements at the best
possible efficiency. The SC600 has three charge pump
configurations (modes), which multiply the input voltage
by 1x, 1.5x and 2x.
The charge pump configurations are implemented with
two switched or 'bucket' capacitors plus the input and out-
put capacitor. The bucket capacitors are configured for 1x
mode at start-up to source current to the output capacitor
and bring the output up quickly. The charge pump will
begin switching in 1.5x mode. During normal operation,
starting with a fully charged Li-Ion cell, the battery voltage
will begin at about 4.1V. As the battery discharges and
the voltage decays, the SC600 will eventually transition to
2x mode when the battery voltage is approximately 3.50V.
Hysteresis is provided to prevent mode toggling. The out-
put is prevented from exceeding 6.0V. This feature allows
the use of 6.3V ceramic capacitors.
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Advantage
The plot on page 1 shows the efficiency of the SC600A.
An example of a 5.0V regulated charge pump doubler is
plotted to demonstrate how effective the SC600’s 1.5x
mode is at improving efficiency when the input voltage is
above 3.5V. Most of the Li-Ion battery life is above 3.5V
where the SC600 achieves more than 20% higher effi-
ciency compared to the 5.0V regulated charge pump dou-
bler with only a 2x mode. Following the efficiency curve
from left to right as the battery discharges, the SC600A
5.0V remains in 1.5x mode until 3.5V and then transitions
to 2x mode.
Component Versions
There are four versions of the SC600. The component
selection table on page 4 highlights the differences be-
tween the component types. The three basic differences
between the component versions are in the output volt-
age, maximum output current capability, and the mode
transition point.
The mode transition point is the value of input voltage at
which the component will transition between 1.5x and 2x
modes. 5.0V, 4.5V, and 4.0V versions are available. The
SC600A (5.0V) is most efficient for applications that use
up to 60mA. The SC600B (4.5V) and SC600C (4.5V) have
different maximum output currents and mode transition
points. The lower mode transition point of the SC600C
allows it to remain in 1.5x mode longer for greater power
savings.
The SC600B has higher output capability, up to 120mA,
and S600C is rated for 60mA. The SC600D (4.0V) is for
applications using up to 120mA.
Start-Up Conditions
Typical start-up time is less than 50μs.
Caution: The SC600
must be enabled while 650kHz or 262kHz is selected to pre-
vent over-voltage during start-up.
LED Bias and Backlighting Applications
When using the SC600 for LED bias, note that the SC600C
and SC600D require the same input power per unit of
output current even though the SC600C is more efficient.
Also, the SC600A will have the same input power as the
SC600B though the SC600A is more efficient.
The following plots of Input Power vs. Input Voltage high-
light the differences in application of the four component
versions. To achieve the lowest possible input power, it
is desirable for the charge pump to remain in 1.5x mode
until the input voltage is as low as possible. The transi-
tion points from 1.5x to 2x are identified in the plot where
the input power steps upward as the input voltage moves
lower.
©
2006 Semtech Corp.
7
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