User's Guide
SNAA064C – November 2008 – Revised May 2013
AN-1922 LM48511 Evaluation Board
1
Introduction
To help the user investigate and evaluate the LM48511SQ performance and capabilities, a fully populated
demonstration board was created. This board is shown in Figure 1. Connected to an external power
supply (3.0V ≤ VDD ≤ 5.5V) and a signal source, the LM48511SQ demonstration board easily exercises the
amplifier’s features.
Figure 1. Typical LM48511SQ Demonstration Board
2
Quick Start Guide
Step 1. Apply a 3.0V to 5.5V power supply voltage to the VDD pin with respect to the ground (GND) pin.
Step 2. Set connectors SD_Amp, SS_En Enable, SD_Boost to High. Set FB_SEL to Low which boosts
the regulator output voltage PV1 to about 7.6V.
Step 3. Apply a mono differential input signal into the Audio Input’s two center pins of the 4-pin connector.
Step 4. Apply power. Make measurements.
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AN-1922 LM48511 Evaluation Board
1
General Description
3
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General Description
The Texas Instruments LM48511 integrates a boost converter with a high efficiency Class D audio power
amplifier to provide 3W continuous power into an 8Ω speaker when operating from a 5V power supply.
When operating from a 3V to 4V power supply, the LM48511 can be configured to drive 1 to 2.5W into an
8Ω load with less than 1% distortion (THD+N). The Class D amplifier features a low noise PWM
architecture that eliminates the output filter, reducing external component count, board area consumption,
system cost, and simplifying design. A selectable spread spectrum modulation scheme suppresses RF
emissions, further reducing the need for output filters. The LM48511’s switching regulator is a currentmode boost converter operating at a fixed frequency of 1MHz. Two selectable feedback networks allow
the LM48511 regulator to dynamically switch between two different output voltages, improving efficiency
by optimizing the amplifier’s supply voltage based on battery voltage and output power requirements. The
LM48511 is designed for use in portable devices, such as GPS, mobile phones, and MP3 players. The
high, 80% efficiency at 5V, extends battery life when compared to boosted Class AB amplifiers.
Independent regulator and amplifier shutdown controls optimize power savings by disabling the regulator
when high output power is not required.
The gain of the LM48511 is set by external resistors, which allows independent gain control from multiple
sources by summing the signals. Output short circuit and thermal overload protection prevent the device
from damage during fault conditions. Superior click and pop suppression eliminates audible transients
during power-up and shutdown.
4
Board Features
The LM48511SQ 3W, Ultra-Low EMI, Filterless, Mono, Class D Audio Power Amplifier with Spread
Spectrum demonstration board has all of the necessary connections using 0.100” headers connectors to
apply the power supply voltage, audio input signals, and audio output (speaker). The amplified audio
signal is only available on the audio output header.
5
Operating Conditions
Temperature Range:
2
TMIN ≤ TA ≤ TMAX
–40°C ≤ TA ≤ +85°C
Supply Voltage (VDD)
3.0V ≤ VDD ≤ ±5.5V
Amplifier Voltage (PV1, V1)
4.8V ≤ PV1 ≤ ±8.0V
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Application Circuit Schematic
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Application Circuit Schematic
VDD
20
21
GND2
1
VDD
24
5
17
GND2
Audio Input
1
1
GND2
2
2
3
3
4
GND2
4
CIN+
R5
20k
CIN-
R7
180 nF
20k
16
15
14
GND1
GND
2
3
GND3
GND1
22
GND3
23
FB_GND0
FB_GND1
FB_SEL
V1
LM48511SQ
/SD_Boost
PV1
13
10
/SD_Amp
VGO-
LS+
8
Speaker
2
IN+
INVGO+
VDD
SS_EN
1
GND2
C4
1 PF
3
GND3
R8
20k
GND2
GND3
FB
6
180 nF
R6
20k
Softstart
LS-
GND2
4
19
C3
1 PF
12
1
7
+
R2
9.31k 100 nF
GND3
GND2
SW
R1
4.87k
100 PF
2
CSoftstart
GND2
FB_SEL VDD
1
1
2
2
3
GND2
3
+C2
SW
GND3
1 PF
CS3
GND1
SD_Amp
1
1
2
2
3
3
GND3
1 PF
CS2
9
SD_Boost
1
1
2
2
3
3
VDD
10 PF
CS1
6.8 PH
18
GND1 (Class D GND)
GND2 (AGND)
GND3 (Switch GND)
+
D1
L1
VDD
VDD
GND2
2
GND1
+ C1
280 pF
R3
25.5k
R4
2.5k
1
11
VDD
SS-EN
6
GND1 GND1 GND2
1
2
3
GND2
Figure 2. Typical LM48511 Audio Amplifier Application Circuit
7
Connections
Table 1. LM48511 Demonstration Board Connections
Designator
Supply Voltage (VDD)
Audio Input
Speaker (Audio Output)
SD_Amp
SS_EN Enable
SD_Boost
Function or Use
The supply voltage operating range is from 3.0V to 5.5V, but the absolute maximum rating is 9V.
Connect a differential audio source to the two center pins of the Audio Input connector. For a singleended audio source, connect one of the center pins to the adjacent center pin (GND) and connect
the audio source to the remaining center pin.
Connect speaker load across the speaker connector.
Set SD_AMP Low to disable the Class D amplifier.
Set SD_AMP High to enable the Class D amplifier.
Set SS_EN Low to enable Fixed frequency (FF) mode.
Set SS_EN High to enable Spread Spectrum (SS) mode.
Set SD_Boost Low to disable the boost regulator.
Set SD_Boost High to enable the boost regulator.
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Typical Performance Characteristics
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Table 1. LM48511 Demonstration Board Connections (continued)
Designator
Function or Use
Set the FB_SEL High for:
PV1 = VFB {1 + [25.5kΩ / 4.87kΩ]}
where VFB = 1.23V
FB_SEL
8
Set the FB_SEL Low for:
PV1 = VFB {1 + [25.5kΩ /9.31kΩ]}
where VFB = 1.23V
Typical Performance Characteristics
THD+N vs Frequency
VDD = 3.6V, RL = 8Ω
PO = 500mW, filter = 22kHz, PV1 = 4.8V
10
10
1
1
FIXED FREQUENCY
THD+N (%)
THD+N (%)
THD+N vs Frequency
VDD = 5V, RL = 8Ω
PO = 2W, filter = 22kHz, PV1 = 7.8V
0.1
FIXED FREQUENCY
0.1
0.01
0.01
SPREAD SPECTRUM
SPREAD SPECTRUM
0.001
20
200
2k
20k
0.001
20
200
THD+N vs Frequency
VDD = 3V, RL = 8Ω
PO = 1.5W, filter = 22kHz, PV1 = 7V
THD+N vs Output Power
VDD = 5V, RL = 8Ω
PO = 1.5W, f = 1kHz, filter = 22kHz, PV1 = 7.8V
10
10
SPREAD SPECTRUM,
CIN = 180 nF
FIXED FREQUENCY,
CIN = 180 nF
0.1
1
THD+N (%)
THD+N (%)
20k
FREQUENCY (Hz)
FREQUENCY (Hz)
1
2k
SPREAD SPECTRUM
0.1
0.01
SPREAD SPECTRUM, CIN = 1 PF
FIXED FREQUENCY, CIN = 1 PF
0.001
20
200
2k
20k
0.01
10m
FIXED FREQUENCY
AN-1922 LM48511 Evaluation Board
1
5
OUTPUT POWER (W)
FREQUENCY (Hz)
4
100m
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Typical Performance Characteristics
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THD+N vs Output Power
VDD = 3.6V, RL = 8Ω
f = 1kHz, filter = 22kHz, PV1 = 7V
THD+N vs Output Power
VDD = 3V, RL = 8Ω
f = 1kHz, filter = 22kHz, PV1 = 4.8V
10
10
THD+N (%)
1
1
THD+N (%)
FIXED FREQUENCY
SPREAD SPECTRUM
0.1
0.01
10m
FIXED FREQUENCY
SPREAD SPECTRUM
0.1
100m
1
0.01
10m
5
OUTPUT POWER (W)
100m
1
5
OUTPUT POWER (W)
THD+N vs Output Power
VDD = 3V, 3.6V, 5V, RL = 8Ω
f = 1kHz, filter = 22kHz, R1 = 4.87kΩ, FF
THD+N vs Output Power
VDD = 3.6V, RL = 8Ω
filter = 22kHz, PV1 = 7.8V, PV1 = 7V, PV1 = 4.8V, FF
10
10
3V
9.31 k:
THD+N (%)
1
THD+N (%)
1
3.6V
0.1
5.35 k:
4.87 k:
0.1
5V
0.01
10m
100m
1
5
0.01
10m
OUTPUT POWER (W)
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100m
1
5
OUTPUT POWER (W)
AN-1922 LM48511 Evaluation Board
5
Typical Performance Characteristics
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Boost Amplifier vs Output Power
VDD = 3.6V, RL = 8Ω
f = 1kHz, PV1 = 7V
100
100
90
90
80
80
70
70
EFFICIENCY (%)
EFFICIENCY (%)
Boost Amplifier vs Output Power
VDD = 5V, RL = 8Ω
f = 1kHz, PV1 = 7.8V
60
50
40
30
60
50
40
30
20
20
10
10
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
4.0
0
0.5
1.0
1.5
2.0
2.5
3.0
OUTPUT POWER (W)
OUTPUT POWER (W)
Boost Amplifier vs Output Power
VDD = 3V, RL = 8Ω
f = 1kHz, PV1 = 4.8V
PSRR vs Frequency
VDD = 5V, RL = 8Ω
VRIPPLE = 200mVPP, PV1 = 7.8V
0
100
90
-20
70
PSRR (dB)
EFFICIENCY (%)
80
60
50
40
-40
FIXED FREQUENCY
-60
SPREAD SPECTRUM
30
-80
20
10
0
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
-100
20
200
AN-1922 LM48511 Evaluation Board
20k
FREQUENCY (Hz)
OUTPUT POWER (W)
6
2k
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Typical Performance Characteristics
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PSRR vs Frequency
VDD = 3V, RL = 8Ω
VRIPPLE = 200mVPP, PV1 = 4.8V
0
0
-20
-20
-40
PSRR (dB)
PSRR (dB)
PSRR vs Frequency
VDD = 3.6V, RL = 8Ω
VRIPPLE = 200mVPP, PV1 = 7V
FIXED FREQUENCY
-60
SPREAD SPECTRUM
-40
-60
SPREAD SPECTRUM
-80
-80
-100
20
200
2k
20k
FIXED FREQUENCY
-100
20
200
FREQUENCY (Hz)
2k
20k
FREQUENCY (Hz)
Supply Current vs Supply Voltage
PV1 = 7.8V
Supply Current vs Supply Voltage
PV1 = 7V
30
23
SPREAD SPECTRUM
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
21
25
20
15
FIXED FREQUENCY
10
SPREAD SPECTRUM
19
17
15
13
11
FIXED FREQUENCY
9
7
5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
5
2.5
SUPPLY VOLTAGE (V)
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3.0
3.5
4.0
4.5
5.0
5.5
6.0
SUPPLY VOLTAGE (V)
AN-1922 LM48511 Evaluation Board
7
Typical Performance Characteristics
www.ti.com
Power Dissipation vs Output Power
VDD = 5V, RL = 8Ω
PV1 = 7.8V, FF
Supply Current vs Supply Voltage
PV1 = 4.8V
11
1.8
1.6
POWER DISSIPATION (W)
SUPPLY CURRENT (mA)
10
SPREAD
SPECTRUM
9
8
7
6
3.0
3.5
4.0
4.5
1.2
1.0
0.8
0.6
0.4
0.2
FIXED FREQUENCY
5
2.5
1.4
5.0
5.5
0
6.0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
OUTPUT POWER (W)
SUPPLY VOLTAGE (V)
Power Dissipation vs Output Power
VDD = 3.6V, RL = 8Ω
PV1 = 7V, FF
Power Dissipation vs Output Power
VDD = 3V, RL = 8Ω
PV1 = 4.8V, FF
1.8
0.5
POWER DISSIPATION (W)
POWER DISSIPATION (W)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.4
0.3
0.2
0.1
0.2
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
0
0.2
OUTPUT POWER (W)
8
AN-1922 LM48511 Evaluation Board
0.4
0.6
0.8
1.0
1.2
1.4
1.6
OUTPUT POWER (W)
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Typical Performance Characteristics
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Boost Converter Efficiency
vs
ILOAD(DC)
VDD = 3.6V, PV1 =7V
100
100
90
90
80
80
70
70
EFFICIENCY (%)
EFFICIENCY (%)
Boost Converter Efficiency
vs
ILOAD(DC)
VDD = 5V, PV1 = 7.8V
60
50
40
30
60
50
40
30
20
20
10
10
0
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0
0.1
LOAD CURRENT (A)
0.2
0.3
0.4
0.5
0.6
LOAD CURRENT (A)
Boost Converter Efficiency
vs
ILOAD(DC)
VDD = 3V, PV1 = 4.8V
100
90
EFFICIENCY (%)
80
70
60
50
40
30
20
10
0
0
0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.4
LOAD CURRENT (A)
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9
PCB Layout Guidelines
9
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PCB Layout Guidelines
This section provides general practical guidelines for PCB layouts that use various power and ground
traces. Designers should note that these are only “rule-of-thumb” recommendations and the actual results
are predicated on the final layout.
9.1
Power and Ground Circuits
Star trace routing techniques can have a major positive impact on low-level signal performance. Star trace
routing refers to using individual traces that radiate from a signal point to feed power and ground to each
circuit or even device.
9.2
Layout Helpful Hints:
1. Avoid routing traces under the inductor.
2. Use three separate grounds that eventually connect to one point:
(a) Signal or quiet ground (GND2)
(b) Ground for the LM48511 device (GND1)
(c) SW (GND3) (switch ground). This trace for the switch ground carries the heaviest current (3A) and
therefore is the nosiest. Make this trace as wide and short as possible and keep at a distance from
the quiet ground and device ground. Give distance priority to the quiet ground.
10
Bill Of Materials
Designator
Footprint
Qty
Value
Cf1
CHIP CAPACITOR GENERIC
Description
CAP 0805
1
470pF
CINA
CHIP CAPACITOR GENERIC
CAP 1210
1
1μF
CINB
CHIP CAPACITOR GENERIC
CAP 1210
1
1μF
Co
CHIP CAPACITOR GENERIC
CAP 1210
1
10μF
Cs1
CHIP CAPACITOR GENERIC
CAP 1210
1
2.2μF
Cs2
CHIP CAPACITOR GENERIC
CAP 1210
1
4.7μF
D1
SCHOTTKY DIODE
DIODE MBR0520 IR
1
L1
11
IND_COILCRAFT-DO1813P
1
4.7μH
R1
CHIP RESISTOR GENERIC
RES 0805
1
41.2K
R2
CHIP RESISTOR GENERIC
RES 0805
1
13.3K
RINA
CHIP RESISTOR GENERIC
RES 0805
1
150K
RINB
CHIP RESISTOR GENERIC
RES 0805
1
150K
Demonstration Board PCB Layout
Figure 3 through Figure 8 shows the different layers used to create the LM48511SQ demonstration board.
Figure 3 is the silkscreen that shows component locations on the board’s top surface. Figure 4 is the
metal Top Layer. Figure 5 is the metal Midlayer 1. Figure 6 is the metal Midlayer 2. Figure 7 is the metal
Bottom Layer. Figure 8 is the silkscreen that shows component locations on the board bottom.
10
AN-1922 LM48511 Evaluation Board
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Demonstration Board PCB Layout
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Figure 3. Top Silkscreen
Figure 4. Top Layer
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Demonstration Board PCB Layout
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Figure 5. Mid Layer 1
Figure 6. Mid Layer 2
12
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Demonstration Board PCB Layout
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Figure 7. Bottom Layer
Figure 8. Bottom Overlay
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Revision History
12
14
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Revision History
Rev
Date
1.0
11/05/08
Initial release.
Description
1.01
08/05/11
Changed the title of Table 1 from LME49600 to LM48511.
1.02
10/18/12
Edited Table 1 (Demonstration Board Connections). Edited Figure 2 (Typical LM48511 Audio
Amplifier Circuit).
AN-1922 LM48511 Evaluation Board
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