Texas Instruments AN-1922 LM48511 User Manual

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.

User's Guide

SNAA064C–November 2008–Revised May 2013

AN-1922 LM48511 Evaluation Board

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

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 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.

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5 Operating Conditions

Temperature Range: T
Supply Voltage (VDD) 3.0V ≤ VDD≤ ±5.5V
Amplifier Voltage (PV1, V1) 4.8V ≤ PV1≤ ±8.0V

MIN

≤ TA≤ T

MAX

–40°C ≤ TA≤ +85°C

2

AN-1922 LM48511 Evaluation Board SNAA064C–November 2008–Revised May 2013

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Softstart

19

FB

20

FB_GND0

21

FB_GND1

1

FB_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 PFC41 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_EN

1
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

4

GND2

3

3

1
2

VDD

VDD

GND2

GND2

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6 Application Circuit Schematic

Application Circuit Schematic

7 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 ended audio source, connect one of the center pins to the adjacent center pin (GND) and connect

Speaker (Audio Output) Connect speaker load across the speaker connector.

SD_Amp

SS_EN Enable

SD_Boost

SNAA064C–November 2008–Revised May 2013 AN-1922 LM48511 Evaluation Board

Figure 2. Typical LM48511 Audio Amplifier Application Circuit

Table 1. LM48511 Demonstration Board Connections

Connect a differential audio source to the two center pins of the Audio Input connector. For a single­the audio source to the remaining center pin.

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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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, C

IN

= 1 PF

FIXED FREQUENCY, C

IN

= 1 PF

SPREAD SPECTRUM,
C

IN

= 180 nF

FIXED FREQUENCY,
C

IN

= 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

Table 1. LM48511 Demonstration Board Connections (continued)

Designator Function or Use

Set the FB_SEL High for:

PV1 = VFB {1 + [25.5kΩ / 4.87kΩ]}

FB_SEL

where VFB= 1.23V

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

PO= 2W, filter = 22kHz, PV1= 7.8V PO= 500mW, filter = 22kHz, PV1= 4.8V

VDD= 5V, RL= 8Ω VDD= 3.6V, RL= 8Ω

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THD+N vs Frequency THD+N vs Output Power

VDD= 3V, RL= 8Ω VDD= 5V, RL= 8Ω

PO= 1.5W, filter = 22kHz, PV1= 7V PO= 1.5W, f = 1kHz, filter = 22kHz, PV1= 7.8V

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AN-1922 LM48511 Evaluation Board SNAA064C–November 2008–Revised May 2013

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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

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Typical Performance Characteristics

THD+N vs Output Power THD+N vs Output Power

VDD= 3.6V, RL= 8Ω VDD= 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= 8Ω VDD= 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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