National Semiconductor LM48821 Manual de usuario

LM48821 Evaluation Board

User's Guide

National Semiconductor

Application Note 1589

Kevin Hoskins

May 2007

Quick Start Guide

Connect the I2C signal generation and interface board to a

computer’s parallel port.

Install LM48821 control software: “LM48821_Software.”

Amplifier output mode:

Apply a 2.0V to 4.0V power supply’s positive voltage output

to the “VDD” pin on jumper J6. Apply the power supply’s

ground return to the “GND“ pin on J6.

Connect the supplied 5-wire cable between the I2C signal

generation and interface board and the 5-pin connector (I2C

Interface) on the LM48821 demonstration board.

Apply a stereo audio signal to jumpers JP2(Left) and JP3

(Right). Apply the source’s +input and -input to the “+” pin and

the “-“ pin, respectively.

Connect a load (≥ 16Ω) to JP(Right) and another load to JP5

(Left). JP4’s “+” pin and JP’s “+” pin carries the output signals

from the two amplifiers found on pins OUTR and OUTL, re-

spectively.

Apply power. Make measurements. Plug in a pair of head-

phones. Enjoy.

Introduction

To help the user investigate and evaluate the LM48821's per-

formance and capabilities, a fully populated demonstration

board is available from the National Semiconductor

Corporation's Audio Products Group. This board is shown in

Figure 1. Connected to an external power supply (2.0V to

4.0V), a signal source and an I2C controller (or signal source),

the LM48821 demonstration board easily demonstrate the

amplifier's features.

30009811

FIGURE 1. The LM48821 Demonstration Board

LM48821 Evaluation Board User's Guide AN-1589

General Description

The LM48821 is a fully differential input stereo headphone

audio amplifier with an internal digitally controlled volume

control. The LM48821 is optimized to operate over a power

supply voltage range of 2.0V to 4.0V. This amplifier is capable

of delivering 53mWRMS per channel into a 32Ωload at 1%

THD when powered by a 3.0V power supply.

Boomer audio power amplifiers were designed specifically to

provide high quality output power with a minimal amount of

external components. To that end, the LM48821 features two

functions that optimize system cost and minimize PCB area:

an integrated, digitally controlled (I2C bus) volume control and

an amplifier generated negative power supply voltage that

eliminates output signal-coupling capacitors. Since the

LM48821 does not require bootstrap capacitors, snubber net-

works, or output coupling capacitors, it is optimally suited for

low-power, battery powered potable systems.

The LM48821 includes separate shutdown controls for each

stereo channel for micropower dissipation, an internal thermal

shutdown protection mechanism, and is unity gain stable.

Operating Conditions

■ Temperature Range –40°C ≤TA≤85°C

■ Amplifier Power

Supply Voltage 2.0V ≤VDD ≤5.0V ≤4.0V

Board Features

The LM48821 demonstration board has all of the necessary

connections, using 0.100” headers, to apply the power supply

voltage, the audio input signals, and the I2C signal inputs. The

amplified audio signal is available on both a stereo head-

phone jack and auxiliary output connections.

Also included with the demonstration board is an I2C signal

generation board and software. With this board and the soft-

ware, the user can easily control the LM48821’s, shutdown

function, mute, and stereo volume control. Figure 3 shows the

software’s graphical user interface.

Schematic

Figure 2 shows the LM48821 Demonstration Board schemat-

ic. Refer to Table 3 for a list of the connections and their

functions.

30009846

Figure 2. The LM48821 Demonstration Board Schematic

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Connections

Connecting to the world is accomplished through the 0.100”

headers on the LM48821 demonstration board. The functions

of the different headers are detailed in Table 1.

TABLE 1. LM48821 Demonstration Board Connections

Jumper Designation Function or Use

J1 Stereo, 0.125” headphone jack. Left channel is on the tip connector

and the right channel is on the ring connector. Ground is on the sleeve

connector.

J2 This is the connection to the amplifier’s differential left channel input.

Apply an external differential signal source’s positive voltage to the J2

pin labeled “L IN+” and the signal source’s negative input to the pin

labeled “L IN-.”

J3 This is the connection to the amplifier’s differential right channel input.

Apply an external differential signal source’s positive voltage to the J3

pin labeled “R IN+” and the signal source’s negative input to the pin

labeled “R IN-.”

J4 This is the connection to the amplifier’s single-ended, ground-

referenced right channel output. Connect the J4 pin labeled “R OUT

+” and the pin labeled “R OUT-” to the positive and ground inputs,

respectively, of an external signal measurement device. J4’s pin

labeled “R OUT+” corresponds to the headphone jack’s “ring”

connection. J4’s pin labeled “R OUT-“ corresponds to the headphone

jack’s “sleeve” (or ground) connection.

J5 This is the connection to the amplifier’s single-ended, ground-

referenced left channel output. Connect the J5 pin labeled “L OUT+”

and the pin labeled “L OUT-” to the positive and ground inputs,

respectively, of an external signal measurement device. J5’s pin

labeled “L OUT+” corresponds to the headphone jack’s “tip”

connection. J5’s pin labeled “L OUT-“ corresponds to the headphone

jack’s “sleeve” (or ground) connection.

J6 Power supply connection. Connect an external power supply’s

positive voltage source (2.0V to 4.0V) to the J6 pin labeled “VDD” and

the supply’s ground source to the pin labeled “GND.”

J8 (I2C Interface) This is the input connection for the I2C serial clock and serial data

signals. J8-pin 1 is for the SCL signal, JP8-pin 2 is not used. J8-pin 3

is for the SDA signal. J8-pin 4 is for an I2C VDD supply voltage supplied

by the I2C signal source. J8-pin 5 is for ground.

JU1 If an external I2C power supply voltage is used, connect this supply’s

positive voltage source to the JU1 pin labeled “I2CVDD” and the

supply’s ground source to the pin labeled “GND.” If the external VDD

power supply is used for the I2CVDDvoltage, place a jumper between

the JU1 pin labeled “VDD” and the JU1 pin labeled “I2CVDD.”

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Power Supply Sequencing

The LM48821 uses two power supply voltages: VDD for the

analog circuitry and I2CVDD, which defines the digital control

logic high voltage level. To ensure proper functionality, apply

VDD first, followed by I2CVDD. If one power supply is used,

VDD and I2CVDD can be connected together. The part will

power-up with both channels shutdown, the volume control

set to minimum, and the mute function active.

I2C Signal Generation Board and

Software

The I2C signal generation and interface board, along with the

LM48821 software, will generate the address byte and the

data byte used in the I2C control data transaction. To use the

I2C signal generation and interface board, please plug it into

a PC’s parallel port (on either a notebook or a desktop com-

puter).

The software comes with an installer. To install, unzip the file

titled “LM48821_Software.” After the file unzips, double-click

the “setup.exe” file. After it launches, please follow the

installer’s instructions. Setup will create a folder named

“LM48821” in the “Program” folder on the “C” disk (if the de-

fault is used) along with a shortcut of the same name in the

“Programs” folder in the “Start” menu.

30009810

Figure 3. The LM48821 Software User's Interface

The LM48821 program includes controls for the amplifier’s

volume control, individual channel shutdown, and the mute

function. The control program's on-screen user interface is

shown in Figure 3.

The Default button is used to return the LM48821 to its power-

on reset state: minimum volume setting, shutdown on both

amplifiers active, and mute active.

The LM48821’s stereo VOLUME CONTROL has 32 steps

and a gain range of –76dB to 18dB. It is controlled using the

slider located at the bottom of the program’s window. Each

time the slider is moved from one tick mark to another, the

program updates the amplifier’s volume control.

LEFT CHANNEL, BOTH CHANNELS, and RIGHT CHAN-

NEL controls each have two buttons. For the left and right

channel control, the “ON” button activates its respective chan-

nel, whereas the “OFF” button places its respective channel

in shutdown mode. Selecting the BOTH CHANNELS “ON”

button simultaneously activates both channels, whereas se-

lecting the “OFF” button places channels in shutdown mode.

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 (returning individual traces back

to a central point rather than daisy chaining traces together in

a serial manner) can have a major positive impact on low-level

signal performance. Star trace routing refers to using individ-

ual traces that radiate from a signal point to feed power and

ground to each circuit or even device. This technique may

require greater design time, but should not increase the final

price of the board.

For good THD+N and low noise performance and to ensure

correct power-on behavior at the maximum allowed supply

voltage, a local 4.7μF power supply bypass capacitor should

be connected as physically close as possible to the PVDD pin.

AVOIDING TYPICAL DESIGN/LAYOUT PROBLEMS

Avoid ground loops or running digital and analog traces par-

allel to each other (side-by-side) on the same PCB layer.

When traces must cross over each other, do so at 90 degrees.

Running digital and analog traces at 90 degrees to each other

from the top to the bottom side as much as possible will min-

imize capacitive noise coupling and crosstalk.

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Bill of Materials

Designator Part Description Value Tolerance Rating Package

Type

Manufacturer Manufacturer's

Part Number

C1–C4

TACmicrochip

tantalum

capacitor

0.47μF±20% 10V 0402 AVX TACK474M010PTA

C5, C9

Multilayer

Ceramic

Capacitor

0.1μF±10% 6.3V 0201 TDK C0603X5R1A104M

C6, C8

Multilayer

Ceramic

Capacitor

4.7μF±20% 6.3V 0603 TDK C1608X5R1A475M

Multilayer

Ceramic

Capacitor

4.7μF±20% 10V 0805 TDK C2012X5R1A475M

J1 Headphone Jack

J2–J6 2-pin header,

100mil lead pitch

J8 5-pin header,

100mil lead pitch

JU1 3-pin header,

100mil lead pitch

LM48821Direct

Coupled Tru-

GND, Ultra Low

Noise, 80mW

Differential

Inputs Stereo

Headphone

Amplifier with I2C

Volume Control

National

Semiconductor Corp LM48821TL

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Demonstration Board PCB Layout

Figures 4 through 9 show the different layers used to create

the LM48821 four-layer demonstration board. Figure 4 is the

silkscreen that shows parts location. Figure 5 is the top layer.

Figure 6 is the upper inner layer. Figure 7 is the lower middle

layer. Figure 8 is the bottom layer. Figure 9 is the bottom

silkscreen layer.

30009845

Figure 4. Top Silkscreen (Shown 2.6X actual size)

30009844

Figure 5. Top Layer (Shown 2.6X actual size)

30009842

Figure 6. Upper Middle Layer (Shown 2.6X actual size)

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30009843

Figure 7. Lower Middle Layer (Shown 2.6X actual size)

30009840

Figure 8. Bottom Layer (Shown 2.6X actual size)

30009841

Figure 9. Bottom Silk Layer (Shown 2.6X actual size)

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Typical Performance

Stereo THD+N vs Output Power

RL = 16Ω, AV= 0dB, f = 100Hz

at (from left to right at 1% THD+N):

VDD = 2V, VDD = 3V, VDD = 4V,

both channels driven and measured

30009855

Stereo THD+N vs Output Power

RL = 16Ω, AV= 0dB, f = 1kHz

at (from left to right at 1% THD+N):

VDD = 2V, VDD = 3V, VDD = 4V,

both channels driven and measured

30009853

Stereo THD+N vs Output Power

RL = 16Ω, AV= 0dB, f = 10kHz

at (from left to right at 1% THD+N):

VDD = 2V, VDD = 3V, VDD = 4V,

both channels driven and measured

30009854

Stereo THD+N vs Output Power

RL = 32Ω, AV= 0dB, f = 100Hz

at (from left to right at 1% THD+N):

VDD = 2V, VDD = 3V, VDD = 4V,

both channels driven and measured

30009858

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Stereo THD+N vs Output Power

RL = 32Ω, AV= 0dB, f = 1kHz

at (from left to right at 1% THD+N):

VDD = 2V, VDD = 3V, VDD = 4V,

both channels driven and measured

30009856

Stereo THD+N vs Output Power

RL = 32Ω, AV= 0dB, f = 10kHz

at (from left to right at 1% THD+N):

VDD = 2V, VDD = 3V, VDD = 4V,

both channels driven and measured

30009857

Stereo THD+N vs Frequency

RL = 16Ω, AV= 0dB

at (from left to bottom at 10kHz):

VDD = 2V, POUT = 7mW;

VDD = 3V, POUT = 36mW;

VDD = 4V, POUT = 92mW;

both channels driven and measured

30009851

Stereo THD+N vs Frequency

RL = 32Ω, AV= 0dB

at (from left to bottom at 10kHz):

VDD = 2V, POUT = 10mW;

VDD = 3V, POUT = 38mW;

VDD = 4V, POUT = 85mW;

both channels driven and measured

30009852

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Appendix A LM48821 I2C Control Register

Table B1 shows the actions that are implemented by manipulating the bits within the internal I2C control register.

Table A1. LM48821 I2C Control Register Addressing and Data Format Chart

D7 D6 D5 D4 D3 D2 D1 D0

I2C Address 1 1 1 0 1 1 0 0

Control Register V4 V3 V2 V1 V0 MUTE LEFT ENABLE RIGHT ENABLE

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