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Texas Instruments TPA2013D1 Boost Converter Component Specification Application notes
Application Report
SLOA126 – December 2008
TPA2013D1 Boost Converter Component Specification
Stephen Crump .......................................................................................... Audio and Imaging Products
ABSTRACT
Loss of output power is a common problem in battery-powered systems as the battery
discharges. This problem can be overcome with a boost converter to power the audio
power output amplifiers, like the converter and amplifier in the Texas Instruments
TPA2013D, a single-chip solution. Passive components used with the converter
dramatically affect its operation, so it is necessary to choose these components
carefully. This application report provides a set of rules to enable the user to make
appropriate choices.
1
Introduction
A common problem in battery-powered systems is loss of audio output as the battery discharges. Audio
power must be reduced or limited to the level available at minimum battery voltage or distortion becomes
unacceptable. It is possible to overcome this problem by using a boost converter, a switching device that
boosts battery output to a fixed higher voltage, to power the audio amplifiers. TI’s TPA2013D1 combines a
high-efficiency boost converter with a class-D amplifier to provide an efficient single-chip solution to the
problem.
Basics of boost circuit operation are conceptually fairly simple, but the selection of passive components to
support the boost circuit can be complicated. However, it is possible to recommend components that work
effectively at several different output power levels. These components can be specified in table form to
eliminate the problem of component selection for users. That is the intent of this application report.
2
TPA2013D1 Configuration
The full circuit for the TPA2013D1 is shown in the following reference schematic, which includes its boost
converter and class-D amplifier and the required supporting passive components. The passive
components are input and output capacitors CI and Co and the switching inductor LI plus feedback
resistors Rf and Rg.
Li
Vi
Rg
Rf
Vo C
o
Ci
VDD
SW
So
FBK
VccOUT
VccIN
CLASS -D
AMPLIFIER
SDZb
SDZd
Control
Circuits
OUT –
Si
TPA2013D1
GPIO
OUT+
BOOST
CONVERTER
IN –
IN+
GAIN
GND/open/VDD
(6/15.6/20 dB)
Differential Input
Figure 1. TPA2013D1 Circuit Configuration
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TPA2013D1 Boost Converter Component Specification
1
Input Capacitor
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The passive components must have the following characteristics.
• The inductor must maintain nearly its full-rated value at the input current required at peak output
power.
– It is important to realize that peak inductor current is typically nearly twice output current, because
output power equals input power divided by circuit efficiency. So, peak input current is
approximately peak output current multiplied by output voltage VCC and divided by input voltage
VDD, plus 10% for the efficiency, typically 90% or more for the boost circuit. Because VCC is greater
than VDD, peak inductor current is typically nearly twice peak output current. Inductor LI must be
rated for this peak current.
• Input and output capacitors must maintain nearly their full nominal values at the voltages applied to
them.
– The value of output capacitor Co determines peak-to-peak output ripple voltage ΔV. High values of
∆V can cause difficulty with EMC, so Co must be chosen to limit ΔV to a low value like 30 mV.
• The feedback resistor must have a value of 500 kΩ to provide optimal stability.
For the reasons supporting these rules, see TI application report Passive Component Selection for
TPA2013D1 Boost Converter (SLOA127), which provides full descriptions and equations regarding
passive components.
These rules lead to the recommended sources and part numbers for the capacitors and inductor shown in
the following table. A pair of equations that specify how to select the feedback resistors follows the table.
3
Input Capacitor
Input capacitor CI is a 10-µF, 10-V component. The value of input capacitor CI generally does not vary
with application. The following part numbers are recommended.
Kemet – C1206C106K8PACTU
TDK – C3216X5R1A106KT
Murata – GRM32ER61A106KA01B
Taiyo Yuden – LMK316BJ106KL-TR
4
Switching Inductor and Output Capacitor
Class-D
Output
Power
(W) (1)
Class-D
Load
(Ω)
Minimum
VDD
(V)
Required
VCC
(V)
Max IL
(A)
1
8
3
4.3
0.70
1.6
8
3
5.5
1.13
2
4
3
4.6
1.53
2.3
4
1.8
5.5
2
L
(µH)
Inductor Vendor
Part Numbers
Max
ΔV
(mVpp)
3.3
30
Murata LQH32PN4R7NN0
Toko DE4514C
Coilcraft LPS4018-472
30
Murata LQH55PN3R3NR0
Toko DE4514C
30
Kemet C1206C106K8PACTU
Murata GRM32ER61A106KA01B
Taiyo Yuden LMK316BJ106ML-T
22
3.3
Murata GRM32ER71A226KE20L
Taiyo Yuden LMK316BJ226ML-T
33
6.2
2
Capacitor Vendor
Part Numbers
10
Toko DE2812C
Coilcraft DO3314
Murata LQH3NPN3R3NG0
4.7
(1)
(2)
C (2)
(µF)
Sumida CDRH5D28NP-6R2NC
TDK C4532X5R1A336M
47
30
Murata GRM32ER61A476KE20L
Taiyo Yuden LMK325BJ476MM-T
All power levels are calculated at 1% THD unless otherwise noted.
All values listed are for ceramic capacitors.
TPA2013D1 Boost Converter Component Specification
SLOA126 – December 2008
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Feedback Resistors
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Other components might work effectively at the power levels shown in the preceding table, but they must
maintain the important characteristics of the recommended components to do so.
• If different inductors are used, they must have saturation current and DCR ratings at least as good as
those of the recommended inductors.
• If different capacitors are used, they must have dc voltage ratings of at least 10 V and be made of
X5R, X7R, or better material.
• Their effectiveness must be verified in comparison to the recommended components before committing
to their use.
5
Feedback Resistors
The following equations are used to determine values for the feedback resistors.
• Rf = 499 kΩ. This value helps maintain stability with the LC filter selections in the preceding table.
• Rg = Rf × 0.5/(VCC – 0.5), where the value 0.5 is an internal feedback reference.
6
Results With Recommended Components
The second set of recommended components, producing 1.6 W into 8 Ω at 10% THD+N from 5.5 Vdc,
includes a 4.7-µH inductor and a 10-µF capacitor. The result with these components is shown in the
following graph. Clipping is flat, indicating that the boost circuit output voltage, the power supply to the
amplifier, is essentially constant. The boost circuit operates as expected with these components.
6
Constant
VCC, ~5.5 Vdc
5
Audio Output Voltage - V
4
3
2.2 Wrms With
Expected VOUT
2
1
0
-1
-2
-3
-4
-5
-6
0
0.5
1
t - Time - mS
1.5
2
Figure 2. Output Power With Recommended Inductor
Output power is 2.2 W, approximately what is expected. (Output power at 10% THD+N is about 26% more
than output power at 1% THD+N with flat clipping like that shown in the following graph.)
7
Results With Components That Are Not Recommended
The result with nonrecommended components can fail to meet expectations. An example is shown in the
following graph, where it is compared to the result in the preceding graph. Output power at 10% THD+N is
reduced to 1.7 W. In addition, clipping is not flat, indicating that the boost circuit cannot maintain a
constant output voltage but instead produces high output ripple. With nonrecommended components, the
boost circuit does not perform as expected and causes early clipping.
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Results With Components That Are Not Recommended
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6
5
Sagging
VCC, <5.5 Vdc
Audio Output Voltage - V
4
3
1.7 Wrms With
Reduced VOUT
2
1
0
-1
-2
-3
-4
-5
-6
0
0.5
1
t - Time - mS
1.5
2
Figure 3. Output Power With Saturating Inductor – Not Recommended
The difference between the two results is simply the inductor. In both cases, the nominal inductor value is
4.7 µH, but in the second case the inductor saturates at low output currents. So, it does not permit the
boost converter to transfer the energy for the TPA2013D1 to reach its rated output. This demonstrates the
importance of selecting appropriate passive components for TPA2013D1. Applying the guidelines of this
document makes that selection an easier process.
4
TPA2013D1 Boost Converter Component Specification
SLOA126 – December 2008
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