lm4874mh

Manufacturer Part Numberlm4874mh
Description2.1w Differential Input, Btl Output Stereo Audio Amplifier With Selectable Gain And Shutdown
ManufacturerNational Semiconductor Corporation
lm4874mh datasheet
 


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LM4874
2.1W Differential Input, BTL Output Stereo Audio
Amplifier with Selectable Gain and Shutdown
General Description
The LM4874 features differential stereo inputs, BTL (bridge-
tied load) outputs, and four externally selectable fixed gains.
Operating on a single 5V supply, the LM4874 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
LM4874’s gain is selected using two digital inputs. The nomi-
nal gain values are 6dB, 10dB, 15.6dB, and 21.6dB.
The LM4874 is designed for notebook and other handheld
portable applications. It delivers high quality output power
from a surface-mount package and requires few external
components.
Other features include an active-low micropower shutdown
mode input and thermal shutdown protection.
Key Specifications
BTL output power
j
R
= 3Ω, V
= 5.0V, and THD+N = 1%
L
DD
BTL output power
j
R
= 4Ω, V
= 5.0V, and THD+N = 1%
L
DD
Connection Diagram
See NS Package Number MXA20A for Exposed-DAP TSSOP
Boomer
is a registered trademark of National Semiconductor Corporation.
®
© 2002 National Semiconductor Corporation
BTL output power
j
R
= 8Ω, V
L
DD
Micropower shutdown current
j
PSRR (
1kHz, V
@
j
Features
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
package
Applications
2.1W (typ)
n Notebook computers
n PDAs
n Portable electronic devices
1.9W (typ)
Top View
Order Number LM4874MH
DS200469
August 2002
= 5.0V, and THD+N = 1%
1.2W (typ)
0.1µA (typ)
= 5V, (Fig.1))
62dB (typ)
DD
20046902
www.national.com

lm4874mh Summary of contents

  • Page 1

    ... 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 package Applications 2.1W (typ) n Notebook computers n PDAs n Portable electronic devices 1.9W (typ) Top View Order Number LM4874MH DS200469 August 2002 = 5.0V, and THD 1.2W (typ) 0.1µA (typ) = 5V, (Fig.1)) 62dB (typ) DD 20046902 www.national.com ...

  • Page 2

    Typical Application FIGURE 1. Typical Audio Amplifier Application Circuit www.national.com 2 20046901 ...

  • Page 3

    ... Input Resistance IN Note 1: An LM4874MH that has been properly mounted to a circuit board with a copper heatsink area of at least 2in Note 2: All voltages are measured with respect to the GND pin unless other wise specified. Note 3: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional but do not guarantee specific performance limits ...

  • 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 LM4874MH 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 MH Specific Characteristics THD vs Frequency 8Ω OUT at (from top to bottom at 1kHz 21.6dB 15.6dB 10dB 6dB ...

  • Page 6

    Typical Performance Characteristics MH Specific Characteristics THD vs Output Power 4Ω (from top to bottom at 100mW 21.6dB 15.6dB 6dB 10dB ...

  • Page 7

    Typical Performance Characteristics MH Specific Characteristics THD vs Output Power 8Ω (from top to bottom at 200mW 21.6dB 15.6dB 10dB ...

  • Page 8

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

  • Page 9

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

  • Page 10

    Typical Performance Characteristics MH Specific Characteristics THD vs Output Power 8Ω (from top to bottom at 200mW 21.6dB 15.6dB 6dB 10dB ...

  • Page 11

    Typical Performance Characteristics MH Specific Characteristics Output Power vs Load Resistance f = 1kHz, at (from top to bottom at 20Ω): 5V, THD = 10 5V, THD = 1 3V, THD ...

  • Page 12

    Typical Performance Characteristics MH Specific Characteristics Dropout Voltage vs Power Supply Voltage R = 4Ω 1kHz, both channels driven and loaded (from top to bottom at 4V): positive signal swing, negative signal swing Amplifier Power ...

  • Page 13

    Typical Performance Characteristics MH Specific Characteristics Cross Talk vs Frequency 8Ω Left channel driven, right channel measured Right channel driven, left channel measured Cross Talk vs Frequency ...

  • Page 14

    Typical Performance Characteristics MH Specific Characteristics Cross Talk vs Frequency 8Ω Left channel driven, right channel measured Right channel driven, left channel measured www.national.com (Continued) 200469D4 = 10dB, ...

  • Page 15

    Application Information PCB LAYOUT AND SUPPLY REGULATION CONSIDERATIONS FOR DRIVING 3W AND 4W LOADS Power dissipated by a load is a function of the voltage swing across the load and the load’s impedance. As load imped- ance decreases, load dissipation ...

  • Page 16

    Application Information Table 1. Gain Settings and Input Resistance GAIN 0 GAIN 1 Selected Gain (dB 15 21.6 POWER SUPPLY BYPASSING As with any power amplifier, proper supply bypassing is ...

  • Page 17

    Application Information Bypass Capacitor Value Selection Besides optimizing the input capacitor value, careful consid- eration should be paid to value nected between the BYPASS pin and ground. Since C determines how fast the LM4874 settles to its ...

  • Page 18

    Application Information As mentioned in the External Components section, the inter- nal input resistor and C create a high pass filter that sets the i amplifier’s lower bandpass frequency limit. Find the coupling capacitor’s value using Equation (11 ...

  • Page 19

    Recommended Printed Circuit Board Layout FIGURE 4. Recommended MH PC Board Layout: FIGURE 5. Recommended MH PC Board Layout: FIGURE 6. Recommended MH PC Board Layout: (Continued) 200469D9 Upper Inner-Layer Layout 200469E0 Lower Inner-Layer Layout 200469E1 Bottom-Side Layout 19 www.national.com ...

  • Page 20

    www.national.com 20 ...

  • Page 21

    ... National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. inches (millimeters) unless otherwise noted Exposed-DAP TSSOP Package Order Number LM4874MH 2. A critical component is any component of a life support device or system whose failure to perform ...