Texas Instruments AN-1922 LM48511 User manual

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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General Description www.ti.com
3 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 8Ωspeaker 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
8Ωload 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 current-
mode 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: 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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4Softstart
19 FB
20 FB_GND0
21 FB_GND1
1FB_SEL
24 /SD_Boost
5/SD_Amp
17 VGO-
16 IN+
15 IN-
14 VGO+
LM48511SQ
LS+
LS-
8
12
GND3 22
GND3 23
GND3
SW SW
VDD
2 3
18
PV1 10
V1 13
6.8 PH
L1
10 PF
CS1
GND3
1 PF
CS2
GND3
1 PF
CS3
GND2
VDD D1
+
C2
100 PF
GND3 GND2 GND1
+C3
1 PFC4 1 PF
2
1
Speaker
100 nF
CSoftstart
GND2
R2
9.31k
R1
4.87k
R4
2.5k
+
+
R3
25.5k
C1
280 pF
GND2
7
GND2
GND1
9
GND1
GND1
11
GND1
SS-EN
6
1
2
3
SS_EN1
2
3
VDD
GND2
R8
20k
R6
20k
R5
20k
R7
20k
CIN+
180 nF
CIN-
180 nF
GND3
GND2
GND1
GND
1
2
3
FB_SEL
1
2
3
VDD
GND2
1
2
3
SD_Boost
1
2
3
VDD
GND2
GND1 (Class D GND)
GND2 (AGND)
GND3 (Switch GND)
1
2
3
SD_Amp
1
2
3
VDD
GND2
1
2
4
Audio Input
1
2
4GND2
33
1
2
VDD VDD
GND2
GND2
www.ti.com Application Circuit Schematic
6 Application Circuit Schematic
Figure 2. Typical LM48511 Audio Amplifier Application Circuit
7 Connections
Table 1. LM48511 Demonstration Board Connections
Designator Function or Use
Supply Voltage (VDD) 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 single-
Audio Input ended audio source, connect one of the center pins to the adjacent center pin (GND) and connect
the audio source to the remaining center pin.
Speaker (Audio Output) Connect speaker load across the speaker connector.
Set SD_AMP Low to disable the Class D amplifier.
SD_Amp Set SD_AMP High to enable the Class D amplifier.
Set SS_EN Low to enable Fixed frequency (FF) mode.
SS_EN Enable Set SS_EN High to enable Spread Spectrum (SS) mode.
Set SD_Boost Low to disable the boost regulator.
SD_Boost Set SD_Boost High to enable the boost regulator.
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10
1
0.1
0.01
10m 100m 1 5
OUTPUT POWER (W)
THD+N (%)
SPREAD SPECTRUM
FIXED FREQUENCY
10
0.01
0.1
1
20 200 2k 20k
FREQUENCY (Hz)
THD+N (%)
0.001
SPREAD SPECTRUM, CIN = 1 PF
FIXED FREQUENCY, CIN = 1 PF
SPREAD SPECTRUM,
CIN= 180 nF
FIXED FREQUENCY,
CIN = 180 nF
10
0.01
0.1
1
20 200 2k 20k
FREQUENCY (Hz)
THD+N (%)
0.001
FIXED FREQUENCY
SPREAD SPECTRUM
10
0.01
0.1
1
20 200 2k 20k
FREQUENCY (Hz)
THD+N (%)
0.001
FIXED FREQUENCY
SPREAD SPECTRUM
Typical Performance Characteristics www.ti.com
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 Set the FB_SEL Low for:
PV1 = VFB {1 + [25.5kΩ/9.31kΩ]}
where VFB = 1.23V
8 Typical Performance Characteristics
THD+N vs Frequency THD+N vs Frequency
VDD = 5V, RL= 8ΩVDD = 3.6V, RL= 8Ω
PO= 2W, filter = 22kHz, PV1= 7.8V PO= 500mW, filter = 22kHz, PV1= 4.8V
THD+N vs Frequency THD+N vs Output Power
VDD = 3V, RL= 8ΩVDD = 5V, RL= 8Ω
PO= 1.5W, filter = 22kHz, PV1= 7V PO= 1.5W, f = 1kHz, filter = 22kHz, PV1= 7.8V
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10
1
0.1
0.01
10m 100m 1 5
OUTPUT POWER (W)
THD+N (%)
3V
5V
3.6V
10
1
0.1
0.01
10m 100m 1 5
OUTPUT POWER (W)
THD+N (%)
4.87 k:
5.35 k:
9.31 k:
10
1
0.1
0.01
10m 100m 1 5
OUTPUT POWER (W)
THD+N (%)
SPREAD SPECTRUM
FIXED FREQUENCY
10
1
0.1
0.01
10m 100m 1 5
OUTPUT POWER (W)
THD+N (%)
SPREAD SPECTRUM
FIXED FREQUENCY
www.ti.com Typical Performance Characteristics
THD+N vs Output Power THD+N vs Output Power
VDD = 3.6V, RL= 8ΩVDD = 3V, RL= 8Ω
f = 1kHz, filter = 22kHz, PV1= 7V f = 1kHz, filter = 22kHz, PV1= 4.8V
THD+N vs Output Power THD+N vs Output Power
VDD = 3V, 3.6V, 5V, RL= 8ΩVDD = 3.6V, RL= 8Ω
f = 1kHz, filter = 22kHz, R1= 4.87kΩ, FF filter = 22kHz, PV1= 7.8V, PV1= 7V, PV1= 4.8V, FF
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100
50
40
60
70
90
30
20
1.60
0
OUTPUT POWER (W)
EFFICIENCY (%)
0.2 0.4 0.6 0.8 1.0 1.2 1.4
80
10
0
-20
-40
-60
-80
-10020 200 2k 20k
FREQUENCY (Hz)
PSRR (dB)
FIXED FREQUENCY
SPREAD SPECTRUM
100
50
40
60
70
90
30
20
4.00
0
OUTPUT POWER (W)
EFFICIENCY (%)
0.5 1.0 1.5 2.0 2.5 3.0 3.5
80
10
100
50
40
60
70
90
30
20
3.00
0
OUTPUT POWER (W)
EFFICIENCY (%)
0.5 1.0 1.5 2.0 2.5
80
10
Typical Performance Characteristics www.ti.com
Boost Amplifier vs Output Power Boost Amplifier vs Output Power
VDD = 5V, RL= 8ΩVDD = 3.6V, RL= 8Ω
f = 1kHz, PV1= 7.8V f = 1kHz, PV1= 7V
Boost Amplifier vs Output Power PSRR vs Frequency
VDD = 3V, RL= 8ΩVDD = 5V, RL= 8Ω
f = 1kHz, PV1= 4.8V VRIPPLE = 200mVPP, PV1= 7.8V
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30
5
2.5 6.03.0 3.5 4.0 4.5 5.0 5.5
15
20
25
10
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
SPREAD SPECTRUM
FIXED FREQUENCY
23
5
2.5 6.0
7
9
11
13
15
17
19
21
3.0 3.5 4.0 4.5 5.0 5.5
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
SPREAD SPECTRUM
FIXED FREQUENCY
0
-20
-40
-60
-80
-10020 200 2k 20k
FREQUENCY (Hz)
PSRR (dB)
SPREAD SPECTRUM
FIXED FREQUENCY
0
-20
-40
-60
-80
-100
20 200 2k 20k
PSRR (dB)
FREQUENCY (Hz)
FIXED FREQUENCY
SPREAD SPECTRUM
www.ti.com Typical Performance Characteristics
PSRR vs Frequency PSRR vs Frequency
VDD = 3.6V, RL= 8ΩVDD = 3V, RL= 8Ω
VRIPPLE = 200mVPP, PV1= 7V VRIPPLE = 200mVPP, PV1= 4.8V
Supply Current vs Supply Voltage Supply Current vs Supply Voltage
PV1= 7.8V PV1= 7V
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POWER DISSIPATION (W)
0 3.5
OUTPUT POWER (W)
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0.5 1.0 1.5 2.0 2.5 3.0
1.8
0
POWER DISSIPATION (W)
0 1.6
OUTPUT POWER (W)
0.4 0.6 0.8 1.0 1.2 1.4
0.5
00.2
0.4
0.3
0.2
0.1
11
52.5 6.03.0 3.5 4.0 4.5 5.0 5.5
6
7
8
9
10
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
SPREAD
SPECTRUM
FIXED FREQUENCY
POWER DISSIPATION (W)
0 4.0
OUTPUT POWER (W)
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0.5 1.0 1.5 2.0 2.5 3.0 3.5
1.8
0
Typical Performance Characteristics www.ti.com
Power Dissipation vs Output Power
Supply Current vs Supply Voltage VDD = 5V, RL= 8Ω
PV1= 4.8V PV1= 7.8V, FF
Power Dissipation vs Output Power Power Dissipation vs Output Power
VDD = 3.6V, RL= 8ΩVDD = 3V, RL= 8Ω
PV1= 7V, FF PV1= 4.8V, FF
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100
50
40
60
70
90
30
20
0.40
0
LOAD CURRENT (A)
EFFICIENCY (%)
0.05 0.10 0.15 0.20 0.25 0.30 0.35
80
10
100
50
40
60
70
90
30
20
0.70
0
LOAD CURRENT (A)
EFFICIENCY (%)
0.1 0.2 0.3 0.4 0.5 0.6
80
10
100
50
40
60
70
90
30
20
0.60
0
LOAD CURRENT (A)
EFFICIENCY (%)
0.1 0.2 0.3 0.4 0.5
80
10
www.ti.com Typical Performance Characteristics
Boost Converter Efficiency Boost Converter Efficiency
vs vs
ILOAD(DC) ILOAD(DC)
VDD = 5V, PV1= 7.8V VDD = 3.6V, PV1=7V
Boost Converter Efficiency
vs
ILOAD(DC)
VDD = 3V, PV1= 4.8V
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PCB Layout Guidelines www.ti.com
9 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 Description Footprint Qty Value
Cf1 CHIP CAPACITOR GENERIC 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 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
11 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.
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