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Texas Instruments Incorporated
Power Management
Fully integrated TPS6300x buck-boost
converter extends Li-ion battery life
By Bill Johns (Email: w-johns2@ti.com)
HPA Portable Power Applications
Introduction
For portable power applications to take advan-
tage of the small size and high energy density of
modern battery technology, they must operate
efficiently over the full battery-discharge voltage
range. This presents a design challenge for Li-ion-
powered systems requiring a 3.3-V bus. While
standard buck converters excel at efficiently
converting a 4.2- to 3.0-V Li-ion battery to lower
output voltages such as 1.8 V, and standard boost
converters efficiently convert a Li-ion battery to
higher output voltages such as 5 V, neither pro-
vides an optimal solution for generating the ever-
present 3.3-V bus. Topologies such as the SEPIC
and traditional buck-boost utilize the full battery
capacity but suffer from drawbacks such as low
efficiency, high cost, increased board area, and
high part count. The TPS6300x, available in three
configurations, can solve many of these problems.
The TPS63000 has an adjustable output from
1.2 V to 5.5 V. The TPS63001 and TPS63002
outputs are fixed at 3.3 V and 5.0 V, respectively.
All are available in the space-saving 10-pin QFN
(DRC) package.
TPS63001
The Texas Instruments TPS63001 efficiently converts the
Li-ion input to a 3.3-V bus with minimized part count,
small board area, and reduced cost. It integrates both
Figure 1. TPS63001 efficiency at 1.8 to 5.5 V with
320-mA load (V OUT
= 3.3 V)
100
95
90
85
80
75
70
65
60
55
50
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
V
(V)
IN
buck and boost functions into a single 3 × 3-mm QFN
package, including switching FETs, compensation, and
protection features. Only three external parts are required
for operation: input and output capacitors and an inductor.
The converter operates with a peak efficiency of 96% (see
Figure 1). With a peak output current of 800 mA, it delivers
enough current to power most
portable loads. A wide input volt-
age range of 1.8 to 5.5 V allows
operation with many popular power
sources such as dual- and triple-
cell alkaline and NiMH batteries
as well as 3.3- and 5-V buses.
Figure 2 shows a typical 3.3-V
supply that could be powered by
a single Li-ion battery. A switch-
ing frequency of 1.5 MHz allows
the use of a small 2.2-µH inductor
and small 0603-sized ceramic
input and output capacitors. High
efficiency combined with a low
Figure 2. Typical application circuit
L1
µH
2.2
TPS63001
L1
L2
V IN
1.8 to 5.5 V
V OUT
3.3 V
VIN
VOUT
VINA
C1
10 µF
C2
10 µF
EN
FB
PS/SYNC
GND
PGND
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Analog Applications Journal
4Q 2006
High-Performance Analog Products
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Power Management
Texas Instruments Incorporated
external part count reduces the total solution size to only
6 × 6 mm (see Figure 3).
Advanced control topology maximizes efficiency
The TPS6300x is based on the standard H-bridge buck-
boost power stage shown in Figure 4. It contains both
buck and boost switching-FETs configurations that are
connected to a single inductor. Unlike a standard buck-
boost mode that continuously switches all four FETs
simultaneously, the TPS6300x utilizes a proprietary
modulator design that switches only two FETs at a time.
This control scheme significantly reduces unnecessary
switching losses. The TPS6300x also reduces power loss
by operating in the more efficient buck or boost mode
rather than the traditional buck-boost mode.
As the Li-ion battery discharges down to and below 3.3 V,
a buck-boost converter must transition from buck mode to
boost mode. Many buck-boost control schemes exhibit
efficiency drops, power-supply jitter, or unstable output
voltage at this transition point. The TPS6300x transitions
seamlessly between buck and boost modes on a pulse-by-
pulse basis as necessary. This provides constant PWM
switching over the buck and boost range with no overlap
or dead time between the two modes.
Additional features
The TPS6300x contains additional integrated features that
enhance its usability in portable applications that have, for
example, an extremely low quiescent current (less than
50 µA), a user-selectable power-save (PS) mode that main-
tains efficiency at light loads, or external synchronization
to help minimize system noise.
Figure 3. Typical layout in a 6 x 6-mm area
Average-current-mode control topology provides fast
transient response and low output ripple in both buck and
boost modes. Output regulation tolerance is ±1% over the
input and load ranges. Internal compensation is optimized
for an external inductor of 2.2 to 4.7 µH with an output
capacitor between 10 and 22 µF.
Figure 4. Block diagram of power section
Buck
Gate
Drive
Boost
Gate
Drive
+
–
Modulator
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Analog Applications Journal
High-Performance Analog Products
4Q 2006
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Texas Instruments Incorporated
Power Management
Short-circuit protection provides a foldback current
limit that reduces the output current limit from its maxi-
mum value of 1.7 A to 800 mA when the output voltage
falls by 3%.
This reduces power dissipation on the device during an
output overload condition. When the overload has cleared,
normal operation resumes. One advantage of this approach
is the ability to charge large-output capacitors such as
super capacitors.
PS-mode features maintain very high efficiency, even at
light loads below 300 mA. In the PS mode, switching occurs
only long enough to raise the output voltage slightly above
the output-voltage set point. Switching then stops until the
output voltage falls below the set point again. This “on then
off” switching provides excellent efficiency at light loads.
Other applications
The TPS6300x also operates in a current-regulation mode
to drive a white-light-emitting diode (WLED). This is accom-
plished by replacing the output voltage divider network
with a resistor in the return path of the WLED. Since the
typical forward voltage drop of a WLED is 4.2 to 3.5 V,
powering it from a Li-ion cell presents a problem to most
power-supply topologies because the supply is required to
both buck and boost its output voltage. The TPS6300x’s
buck-boost functionality solves this problem and easily
delivers 500 mA of current for a torch or flash application.
Conclusion
The TPS6300x is an ideal solution for converting a Li-ion
battery to a 3.3-V bus. Its features such as high efficiency,
small board area, low cost, and seamless transition from
buck mode to boost mode make it an easy choice for the
design engineer needing a high-performance design with
quick turnaround.
Related Web sites
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Analog Applications Journal
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High-Performance Analog Products
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