Application Report
SNAA042B – May 2007 – Revised May 2013
AN-1614 LM48510 Speaker Application
.....................................................................................................................................................
ABSTRACT
This application report provides information on the performance of the LM48510 and the LM4673 in a
stereo application.
1
2
3
4
Contents
General Description .........................................................................................................
Typical Performance Characteristics .....................................................................................
Application Information .....................................................................................................
3.1
Selecting the Output Voltage (v1) of Boost Converter ........................................................
3.2
Feed-Forward Compensation for Boost Converter ............................................................
3.3
Diode ................................................................................................................
3.4
Inductor ..............................................................................................................
3.5
Calculating Output Current of Boost Converter (IAMP) .........................................................
3.6
Single-Ended Circuit Configuration ..............................................................................
Revision Table ...............................................................................................................
2
3
6
6
6
6
6
7
8
8
List of Figures
....................................................................................
1
LM48510 Stereo Typical Application
2
THD+N vs Frequency VCC = 3.3V, V1 = 5.0V, RL = 15μH+4Ω+15μH PO = 500mW, 22kHz BW .................. 3
3
THD+N vs Frequency VCC = 3.3V, V1 = 5.0V, RL = 15μH+8Ω+15μH PO = 500mW, 22kHz BW .................. 3
4
THD+N vs Frequency VCC = 4.2V, V1 = 5.0V, RL = 15μH+4Ω+15μH PO = 500mW, 22kHz BW .................. 3
5
THD+N vs Frequency VCC = 4.2V, V1 = 5.0V, RL = 15μH+8Ω+15μH PO = 500mW, 22kHz BW .................. 3
6
THD+N vs Output Power VCC = 3.3V, V1 = 5.0V, RL = 15μH+4Ω+15μH 22kHz BW ............................... 3
7
THD+N vs Output Power VCC = 3.3V, V1 = 5.0V, RL = 15μH+8Ω+15μH 22kHz BW ............................... 3
8
THD+N vs Output Power VCC = 4.2V, V1 = 5.0V, RL = 15μH+4Ω+15μH 22kHz BW ............................... 3
9
THD+N vs Output Power VCC = 4.2V, V1 = 5.0V, RL = 15μH+8Ω+15μH 22kHz BW ............................... 3
10
Power Dissipation vs Output Power VCC = 3.3V
11
Power Dissipation vs Output Power VCC = 4.2V
12
13
14
15
16
17
18
19
........................................................................
........................................................................
Power Supply vs Output Power VCC = 3.3V .............................................................................
Power Supply vs Output Power VCC = 4.2V .............................................................................
Supply Current vs Supply Voltage RL = ∞................................................................................
Boost Load vs Output Power VDD = 3.3V, RL = 4Ω ......................................................................
Boost Load vs Output Power VDD = 3.3V, RL = 8Ω ......................................................................
Boost Load vs Output Power VDD = 4.2V, RL = 4Ω ......................................................................
Boost Load vs Output Power VDD = 4.2V, RL = 8Ω ......................................................................
Inductor Current .............................................................................................................
2
4
4
4
4
4
4
5
5
5
7
List of Tables
1
LM48510SD + LM4673SD Demoboard .................................................................................. 2
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AN-1614 LM48510 Speaker Application
Copyright © 2007–2013, Texas Instruments Incorporated
1
General Description
1
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General Description
The LM48510 integrates a switching boost converter with a high efficiency mono Class D audio power
amplifier and can be used in either mono or stereo speaker applications. For stereo applications, an
external Class D audio power amplifier (LM4673) is used in conjunction with the LM48510. For further
information on the LM48510 or the LM4673, refer to their respective datasheets.
L1
4.7 PH
CS1
+
-
VDD
D1
2.2 PF
Co
Cf1
R1
470 pF
VDD
10 PF
41.2 k:
SW
GND2
FB
R2
GND3
SDBOOST
SDBOOST
SDAMP
SDAMP
1 PF
13.3 k:
PV1
LM48510
CS2
V1
4.7 PF
GND1
150 k:
-IN
CINA
RINA
VO1
1 PF
150 k:
VO2
+IN
CINB
RINB
CS4
2.2 PF
1 PF
CS3
4.7 PF
PVDD
VDD
150 k:
-IN
CINC
RINC
1 PF
150 k:
LM4673
VO1
VO2
+IN
CIND
RIND
GND
PGND
Figure 1. LM48510 Stereo Typical Application
Table 1. LM48510SD + LM4673SD Demoboard
RefDes
2
Part Type
Manufacturer
Value
CF1
GRM219R72A471KA01D
Murata
470pF, 0805, Ceramic
CINA, CINB, CINC, CIND
GRM21BR71H105KA12L
Murata
1μF, 0805, Ceramic
CO
GRM32DR71E106KA12L
Murata
10μF, 1210, Ceramic
CS1, CS4
GRM32RR71E225KA01L
Murata
2.2μF, 1210, Ceramic
CS2, CS3
GRM32DR71E475KA61L
Murata
4.7μF, 1210, Ceramic
D1
DIODE_MBR0520_IR
International Rectifier
DIODE
L1
D01813H-472MLB
Coilcraft
4.7μH
R1
RES_0805_CHIP
Any
41.2K
R2
RES_0805_CHIP
Any
13.3K
RINA, RINB, RINC, RIND
RES_0805_CHIP
Any
150K
AN-1614 LM48510 Speaker Application
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Typical Performance Characteristics
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2
Typical Performance Characteristics
10
10
1
1
LM48510
THD+N (%)
THD+N (%)
LM48510
LM4673
0.1
0.01
20
100
1k
0.1
0.01
10k 20k
LM4673
20
100
FREQUENCY (Hz)
Figure 3. THD+N vs Frequency
VCC = 3.3V, V1 = 5.0V, RL = 15μH+8Ω+15μH
PO = 500mW, 22kHz BW
10
1
1
THD+N (%)
10
LM4673
0.1
LM4673
0.1
LM48510
0.01
10k 20k
FREQUENCY (Hz)
Figure 2. THD+N vs Frequency
VCC = 3.3V, V1 = 5.0V, RL = 15μH+4Ω+15μH
PO = 500mW, 22kHz BW
THD+N (%)
1k
20
100
1k
LM48510
0.01
10k 20k
20
FREQUENCY (Hz)
1k
10k 20k
FREQUENCY (Hz)
Figure 4. THD+N vs Frequency
VCC = 4.2V, V1 = 5.0V, RL = 15μH+4Ω+15μH
PO = 500mW, 22kHz BW
Figure 5. THD+N vs Frequency
VCC = 4.2V, V1 = 5.0V, RL = 15μH+8Ω+15μH
PO = 500mW, 22kHz BW
10
10
1
THD+N (%)
1
THD+N (%)
100
LM4673
0.1
LM4673
0.1
LM48510
LM48510
0.01
10m
100m
1
2
0.01
10m
OUTPUT POWER (W)
Figure 6. THD+N vs Output Power
VCC = 3.3V, V1 = 5.0V, RL = 15μH+4Ω+15μH
22kHz BW
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100m
1
2
OUTPUT POWER (W)
Figure 7. THD+N vs Output Power
VCC = 3.3V, V1 = 5.0V, RL = 15μH+8Ω+15μH
22kHz BW
AN-1614 LM48510 Speaker Application
Copyright © 2007–2013, Texas Instruments Incorporated
3
Typical Performance Characteristics
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1
1
THD+N (%)
10
THD+N (%)
10
LM48510
0.1
LM48510
0.1
LM4673
LM4673
0.01
10m
100m
1
0.01
10m
2 3
OUTPUT POWER (W)
Figure 8. THD+N vs Output Power
VCC = 4.2V, V1 = 5.0V, RL = 15μH+4Ω+15μH
22kHz BW
POWER DISSIPATION (W)
POWER DISSIPATION (W)
2.0
RL = 4:
RL = 8:
1.0
0.5
0.3
0.5
0.7
0.9
4
3
2
1
Figure 11. Power Dissipation vs Output Power
VCC = 4.2V
1.6
1.2
1.4
1.0
RL = 4:
POWER DISSIPATION (W)
POWER DISSIPATION (W)
RL = 8:
OUTPUT POWER (W)
OUTPUT POWER (W)
0.8
0.6
RL = 8:
0.4
0.2
RL = 4:
1.2
1.0
0.8
0.6
RL = 8:
0.4
0.2
0.3
0.5
0.7
0.9
1.1
0.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
OUTPUT POWER (W)
OUTPUT POWER (W)
Figure 12. Power Supply vs Output Power
VCC = 3.3V
4
RL = 4:
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
1.1
Figure 10. Power Dissipation vs Output Power
VCC = 3.3V
0
0.1
2
5
2.5
0
0.1
1
Figure 9. THD+N vs Output Power
VCC = 4.2V, V1 = 5.0V, RL = 15μH+8Ω+15μH
22kHz BW
3.0
1.5
100m
OUTPUT POWER (W)
Figure 13. Power Supply vs Output Power
VCC = 4.2V
AN-1614 LM48510 Speaker Application
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Typical Performance Characteristics
80
800
70
700
BOOST LOAD CURRENT (mA)
SUPPLY CURRENT (mA)
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60
50
40
30
20
10
0
2.7
3.0
3.3
3.6
3.9
4.2
4.5
600
500
400
300
200
100
0
0.1
4.8 5.0
0.5
0.7
1.1
0.9
1.3
OUTPUT POWER (W)
SUPPLY VOLTAGE (V)
Figure 14. Supply Current vs Supply Voltage
RL = ∞
Figure 15. Boost Load vs Output Power
VDD = 3.3V, RL = 4Ω
600
1200
BOOST LOAD CURRENT (mA)
BOOST LOAD CURRENT (mA)
0.3
500
400
300
200
100
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
1000
800
600
400
200
0
1.0
0.1 0.3 0.5 0.7 0.9 1.1 1.3
OUTPUT POWER (W)
1.5 1.7 1.9
OUTPUT POWER (W)
Figure 16. Boost Load vs Output Power
VDD = 3.3V, RL = 8Ω
Figure 17. Boost Load vs Output Power
VDD = 4.2V, RL = 4Ω
BOOST LOAD CURRENT (mA)
700
600
500
400
300
200
100
0
0.1
0.3
0.5
0.7
0.9
1.1
1.3
OUTPUT POWER (W)
Figure 18. Boost Load vs Output Power
VDD = 4.2V, RL = 8Ω
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Application Information
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3
Application Information
3.1
Selecting the Output Voltage (v1) of Boost Converter
The output voltage is set using the external resistors R1 and R2. A value of approximately 13.3kΩ is
recommended for R2 to establish a divider current of approximately 92μA. R1 is calculated using the
formula:
R1 = R2 × (V1 / 1.23 – 1)
3.2
(1)
Feed-Forward Compensation for Boost Converter
Although the LM48510’s internal Boost converter is internally compensated, the external feed forward
capacitor Cf1 is required for stability. Adding this capacitor puts a zero in the loop response of the
converter The recommended frequency for the zero fz should be approximately 6kHz. Cf1 can be
calculated using the formula:
Cf1 = 1 / (2π × R1 × fZ)
3.3
(2)
Diode
A Schottky diode must be used for D1. The voltage rating (minimum) should be at least 5V higher than the
output voltage for safe design margin. The average current rating of the diode should be at least 50%
more than the maximum output load current of the application.
3.4
Inductor
The amount of inductance required depends on the switching frequency, duty cycle and amount of
allowable ripple current. The maximum duty cycle of the boost converter determines the maximum boost
ratio for the output-to-input voltage that the converter can attain in continuous mode of operation. The duty
cycle for a given boost application is defined as:
Duty Cycle = V1 + VDIODE – VDD/V1 + VDIODE – VSW
(3)
Larger inductors provides less inductor ripple current which typically means less output voltage ripple (for
a given size of output capacitor). The ripple current and voltage across the inductor is expressed by the
following equation:
V = L di/dt
(4)
Where V is the voltage across the inductor, di is the ripple current, and dt is the duration for which voltage
is applied.
Larger inductors also mean more power can be delivered to the load. The relation can be seen with the
following equation:
E = L/2 × (Ip)2
(5)
where Ip is the peak value of the inductor current.
Note the Boost converter will limit peak current. This means since IP(max) is fixed, increasing L will
increase the maximum of power available to the load.
6
AN-1614 LM48510 Speaker Application
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Application Information
Inductor Current (A)
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ILOAD
ILOAD
1-DC
Time (PA)
Figure 19. Inductor Current
At low boost ratios such as 3.3V to 5.0V, the Boost Converter loop stability requires that the inductance
not exceed 6.8μH. Smaller inductors may be used in applications that require less output current due to
the higher ripple current.
Smaller inductors may be used (and make more sense economically) in applications that require less
output current. Using a smaller inductor means less power can be delivered to the load, see Equation 5.
Note if smaller inductors are used, part may operate in discontinuous mode (where inductor current drops
to zero during switching cycle) using less inductance. This is actually harmless and increases stability
(phase margin) compared to continuous operation.
Best performance is usually obtained when the converter is operated in “continuous” mode at the load
current range of interest, typically giving better load regulation and less out ripple. Continuous operation is
defined as not allowing the inductor current to drop to zero during the cycle. It should be noted that all
boost converters shift over to discontinuous operation as the output load is reduced far enough, but a
larger inductor stays “continuous” over a wider load current range.
Duty cycle affects ripple current since the time the switch is ON determines the length of time that the
current has to ramp up. Any design must be verified for maximum load current over the full temperature
range of the application to make sure the inductance is sufficient.
3.5
Calculating Output Current of Boost Converter (IAMP)
As shown in Figure 19 that depicts the inductor current, the load current is related to the average inductor
current by the relation:
ILOAD = IIND(AVG) × (1-DC)
(6)
where DC is the duty cycle of the application. The switch current can be foun by:
ISW = IIND(AVG) + ½ (IRIPPLE)
(7)
Inductor ripple current is dependent on inductance, duty cycle, input voltage, and frequency:
IRIPPLE = DC × (VIN-VSW) / (fxL)
(8)
Combining all terms, we can develop an expression which allows the maximum available load current to
be calculated:
ILOAD (max) = (1-DC) × (ISW (max) – DC (VIN-VSW) / 2fL
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(9)
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7
Revision Table
3.6
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Single-Ended Circuit Configuration
The Class D can also be used with single-ended sources but input capacitors will be needed to block any
DC at the input terminals (see Figure 1). The typical single-ended application configuration is shown in
Figure 1. The equation for Gain (Equation 10) and the frequency (Equation 11) response remains the
same as if the Class D is configured in Differential mode.
AV = 2 × 150kΩ / Ri
fC = 1 / (2πRi Ci )
4
8
(V/V)
(10)
(Hz)
(11)
Revision Table
Rev
Date
Description
1.0
05/22/07
Initial release.
1.1
08/14/07
Input additional info on the curves' titles.
AN-1614 LM48510 Speaker Application
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