LM4884 NSC [National Semiconductor], LM4884 Datasheet

LM4884

Manufacturer Part Number

LM4884

Description

2.1W Differential Input, BTL Output Stereo Audio Amplifier with RF Suppression and Shutdown

Manufacturer

NSC [National Semiconductor]

Datasheet

1.LM4884.pdf (22 pages)

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LM4884

2.1W Differential Input, BTL Output Stereo Audio

Amplifier with RF Suppression and Shutdown

General Description

The LM4884 features differential stereo inputs, BTL (bridge-

tied load) outputs, and four externally selectable fixed gains.

The LM4884 also features proprietary internal circuitry that

suppresses the coupling of RF signals into the chip. This is

important because certain types of RF signals (such as

GSM) can couple into audio amplifiers in such a way that

part of the signal is heard through the speaker. The RF

suppression circuitry in the LM4884 makes it well-suited for

notebook and portable applications in which strong RF sig-

nals generated by an antenna from a PC wireless card or a

cellular phone may couple audibly into the amplifier.

Operating on a single 5V supply, the LM4884 delivers 1.2W,

1.9W, or 2.1W (typ) of output power to an 8Ω, 4Ω, or 3Ω BTL

load (Note 1), respectively, with less than 1% THD+N. The

LM4884’s gain is selected using two digital inputs. The nomi-

nal gain values are 6dB, 10dB, 15.6dB, and 21.6dB.

Other features of the LM4884 are that it delivers high-quality

output power from a surface-mount package, requires few

external components, has an active-low micropower shut-

down mode input, and has thermal shutdown protection.

Key Specifications

Connection Diagram

Boomer

BTL output power

= 3Ω, V

= 4Ω, V

is a registered trademark of National Semiconductor Corporation.

= 5.0V, and THD+N = 1%

See NS Package Number MXA20A for Exposed-DAP TSSOP

DS201163

Order Number LM4884MH

2.1W (typ)

1.9W (typ)

Top View

Features

n Improved RF immunity, by up to 28dB over previous

n Fully differential input and output

n Internal gain set: 6dB, 10dB, 15.6dB, and 21.6dB

n Improved "click and pop" suppression

n Thermal shutdown protection circuit

n Ultra low current micropower shutdown mode

n 3.0V to 5.5V operation

n Available in space-saving exposed-DAP TSSOP

Applications

n Notebook computers

n PDAs

n Portable electronic devices

designs (such as the LM4874) in selected applications.

package

BTL output power

Micropower shutdown current

PSRR (

= 8Ω, V

20116302

1kHz, V

= 5.0V, and THD+N = 1%

= 5V, (Fig.1))

www.national.com

0.1µA (typ)

1.2W (typ)

62dB (typ)

April 2005

Related parts for LM4884

LM4884 Summary of contents

Page 1

... BTL load (Note 1), respectively, with less than 1% THD+N. The LM4884’s gain is selected using two digital inputs. The nomi- nal gain values are 6dB, 10dB, 15.6dB, and 21.6dB. Other features of the LM4884 are that it delivers high-quality ...

Page 2

Typical Application FIGURE 1. Typical Audio Amplifier Application Circuit www.national.com 2 20116301 ...

Page 3

... ESD Susceptibility (Note 6) Junction Temperature Soldering Information Small Outline Package Vapor Phase (60 sec.) Electrical Characteristics for LM4884 The following specifications applies to the LM4884 when used in the circuit shown in Figure 1 and operating with 6dB, unless otherwise specified. Limits apply for T V Symbol Parameter ...

Page 4

... Note 10: Datasheet minimum and maximum specification limits are guaranteed by design, test, or statistical analysis. Note 11: Output power is measured at the amplifier’s package pins. Note 12: When driving 3Ω or 4Ω loads and operating supply, the LM4884MH must be mounted to a circuit board that has a minimum of 2in uninterrupted copper area connected to the MH package’s exposed DAP. ...

Page 5

Typical Performance Characteristics THD vs Frequency 4Ω 1000mW OUT at (from top to bottom at 1kHz 21.6dB 15.6dB 10dB 6dB V ...

Page 6

Typical Performance Characteristics THD vs Output Power 3Ω (from top to bottom at 50mW 21.6dB 15.6dB 10dB 6dB V V THD ...

Page 7

Typical Performance Characteristics THD vs Output Power 4Ω 20kHz (from top to bottom at 200mW 21.6dB 15.6dB 10dB 6dB ...

Page 8

Typical Performance Characteristics Output Power vs Supply Voltage R = 4Ω 1kHz (from top to bottom at 4V): THD+N = 10%, THD PSRR vs Frequency 4Ω ...

Page 9

Typical Performance Characteristics THD vs Frequency 4Ω OUT at (from top to bottom at 1kHz 21.6dB 15.6dB 10dB 6dB V V THD ...

Page 10

Typical Performance Characteristics THD vs Output Power 4Ω (from top to bottom at 200mW 21.6dB 15.6dB 10dB 6dB V V ...

Page 11

Typical Performance Characteristics PSRR vs Frequency 4Ω SOURCE V = 200mV , at (from top to bottom at 1kHz): RIPPLE P 21.6dB 15.6dB 10dB, ...

Page 12

Typical Performance Characteristics Channel-to-Channel gain Mismatch vs Power Supply Voltage R = 8Ω 1kHz (from top to bottom at 4V 21.6dB 15.6dB 10dB 6dB V ...

Page 13

Typical Performance Characteristics Amplifier Power Dissipation vs Amplifier Load Dissipation 1kHz, at (from top to bottom at 0.3W 4Ω 8Ω, single channel driven and loaded L L Cross Talk ...

Page 14

Typical Performance Characteristics Cross Talk vs Frequency 8Ω Left channel driven, right channel measured Right channel driven, left channel measured Cross Talk vs Frequency V = 3V, R ...

Page 15

... BRIDGE CONFIGURATION EXPLANATION As shown in Figure 1, each of the LM4884’s stereo channels consists of two operational amplifiers. The LM4884 can be used to drive a speaker connected between the two outputs of each channel’s amplifiers. Figure 1 shows that the output of Amp1 serves as the input to Amp2, which results in both amplifiers producing signals identical in magnitude, but 180˚ ...

Page 16

... The capacitors connected to the bypass and power supply pins should be placed as close to the LM4884 as possible. The capacitor connected between the bypass pin and ground improves the internal bias voltage’s stability, (3) producing improved PSRR ...

Page 17

... For this discussion, turn-on refers to either applying the power supply voltage or when the shutdown mode is deactivated. While the power supply voltage is ramping to its final value, the LM4884’s internal amplifiers are configured as unity gain buffers. An (2.83V ) ...

Page 18

... After satisfying the LM4884’s power dissipation require- ments, the minimum differential gain is found using Equation (8). Thus, a minimum gain of 2.83 allows the LM4884’s to reach full output swing and maintain low noise and THD+N perfor- mance. For this example, let the example design, ...

Page 19

Recommended Printed Circuit Board Layout FIGURE 2. Recommended MH PC Board Layout: FIGURE 3. Recommended MH PC Board Layout: (Continued) Component-Side Silkscreen Component-Side Layout 19 20116304 20116305 www.national.com ...

Page 20

Recommended Printed Circuit Board Layout www.national.com FIGURE 4. Recommended MH PC Board Layout: Upper Inner-Layer Layout FIGURE 5. Recommended MH PC Board Layout: Lower Inner-Layer Layout 20 (Continued) 20116306 20116307 ...

Page 21

Recommended Printed Circuit Board Layout FIGURE 6. Recommended MH PC Board Layout: (Continued) Bottom-Side Layout 21 20116308 www.national.com ...

Page 22

... English www.national.com Français Tel: +33 ( 8790 Exposed-DAP TSSOP Package Order Number LM4884MH 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system affect its safety or effectiveness. ...

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