National Semiconductor LM48511 User manual

LM48511 Evaluation Board
User's Guide
National Semiconductor
Application Note 1922
Allan Soriano
November 5, 2008
Quick Start Guide
Apply a 3.0V to 5.5V power supply voltage to the VDD pin with
respect to the ground (GND) pin.
Set connectors SD_Amp, SS_En Enable, SD_Boost to High.
Set FB_SEL to Low (FB_SEL0) which boosts the regulator
output voltage PV1 to about 7.6V.
Apply a mono differential input signal into the Audio Input’s
two center pins of the 4-pin connector.
Apply power. Make measurements.
Introduction
To help the user investigate and evaluate the LM48511SQ
performance and capabilities, a fully populated demonstration
board was created. Please contact National Semiconductor
Corporation’s Audio Products Group for availability. 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.
30085503
FIGURE 1. Typical LM48511SQ Demonstration Board
© 2008 National Semiconductor Corporation 300855 www.national.com
LM48511 Evaluation Board User's Guide AN-1922

General Description
The LM48511 integrates a boost converter with a high effi-
ciency Class D audio power amplifier to provide 3W continu-
ous 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 elimi-
nates the output filter, reducing external component count,
board area consumption, system cost, and simplifying design.
A selectable spread spectrum modulation scheme suppress-
es 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 se-
lectable feedback networks allow the LM48511 regulator to
dynamically switch between two different output voltages, im-
proving 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% effi-
ciency 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 over-
load protection prevent the device from damage during fault
conditions. Superior click and pop suppression eliminates au-
dible transients during power-up and shutdown.
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
Board Features
The LM48511SQ 3W, Ultra-Low EMI, Filterless, Mono, Class
D Audio Power Amplifier with Spread Spectrum demonstra-
tion 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.
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Schematic
30085504
FIGURE 2. Typical LM48511 Audio Amplifier Application Circuit
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Connections
TABLE 1. LME49600 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.
Audio Input The two center pins of the 4 pin connector on the left above are used as differential inputs into the
LM48511, or two single-ended inputs when one center pin and an outer ground pin are paired.
Speaker (Audio Output) The differential output for an 8Ωor 4Ωspeaker.
SD_Amp If SD_Amp is set LOW, the independent internal audio amplifier is disabled, and when set HIGH
the amplifier is enabled.
SS_EN Enable If SS_EN Enable is set LOW, the spread spectrum function is disabled, and when set HIGH the
spread spectrum is enabled.
SD_Boost If SD_Boost is set low, the independent regulator is disabled, and when set HIGH, the regulator is
enabled.
FB_SEL
When LOW (FB_SEL0), the regulator output voltage PV1 is as follows:
PV1 = VFB {1 + [25.5kΩ/ 4.87kΩ]}
where VFB = 1.23V
When LOW (FB_SEL1), the regulator output voltage PV1 is as follows:
PV1 = VFB {1 + [25.5kΩ/9.31kΩ] }
where VFB = 1.23V
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” recommen-
dations and the actual results are predicated on the final
layout.
POWER AND GROUND CIRCUITS
Star trace routing techniques can have a major positive im-
pact 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.
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)
i. This trace for the switch ground carries the heaviest cur-
rent (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.
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Bill Of Materials
Designator Description Footprint Quantity 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
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Demonstration Board PCB Layout
Figures 3 through 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.
30085508
FIGURE 3. Top Silkscreen
30085507
FIGURE 4. Top Layer
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30085505
FIGURE 5. Mid Layer 1
30085506
FIGURE 6. Mid Layer 2
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30085501
FIGURE 7. Bottom Layer
30085502
FIGURE 8. Bottom Overlay
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Typical Performance Characteristics
THD+N vs Frequency
VDD = 5V, RL = 8Ω
PO= 2W, filter = 22kHz, PV1= 7.8V
30085518
THD+N vs Frequency
VDD = 3.6V, RL = 8Ω
PO= 500mW, filter = 22kHz, PV1= 4.8V
30085519
THD+N vs Frequency
VDD = 3V, RL = 8Ω
PO= 1.5W, filter = 22kHz, PV1= 7V
30085520
THD+N vs Output Power
VDD = 5V, RL = 8Ω
PO= 1.5W, f = 1kHz, filter = 22kHz, PV1= 7.8V
30085521
THD+N vs Output Power
VDD = 3.6V, RL = 8Ω
f = 1kHz, filter = 22kHz, PV1= 7V
30085522
THD+N vs Output Power
VDD = 3V, RL = 8Ω
f = 1kHz, filter = 22kHz, PV1= 4.8V
30085523
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THD+N vs Output Power
VDD = 3V, 3.6V, 5V, RL = 8Ω
f = 1kHz, filter = 22kHz, R1= 4.87kΩ, FF
30085524
THD+N vs Output Power
VDD = 3.6V, RL = 8Ω
filter = 22kHz, PV1= 7.8V, PV1= 7V, PV1= 4.8V, FF
30085525
Boost Amplifier vs Output Power
VDD = 5V, RL = 8Ω
f = 1kHz, PV1= 7.8V
30085526
Boost Amplifier vs Output Power
VDD = 3.6V, RL = 8Ω
f = 1kHz, PV1= 7V
30085527
Boost Amplifier vs Output Power
VDD = 3V, RL = 8Ω
f = 1kHz, PV1= 4.8V
30085528
PSRR vs Frequency
VDD = 5V, RL = 8Ω
VRIPPLE = 200mVPP, PV1= 7.8V
30085529
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