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National Semiconductor LM4681 User Manual

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LM4681 Demonstration
Board User's Guide

Quick Start Guide

2
Connect the I
C signal generation and interface board to a
computer's parallel port.
Install LM4681 control software: "LM4681_Software_ver1-
1."
Apply a 3.0V to 5.0V power supply's positive voltage output
to the "I2CVDD" pin on jumper JP6. Apply the power supply's
ground return to the "GND" pin on JP6.
Apply a 9.0V to 15.5V power supply's positive voltage output
to the "VDD" pin on JP1. Apply the power supply's ground
return to the "GND" pin on JP1.
Connect the supplied 5-wire cable between the I
generation and interface board and the 5-pin connector
(JP7) on the LM4681 demonstration board.
Apply a stereo audio signal to jumpers JP4 and JP2. Apply
the source's signal and ground to the "IN1" pin and the
"GND" pin, respectively.
© 2006 National Semiconductor Corporation
National Semiconductor
Application Note 1488
Kevin Hoskins
May 2006
Connect a load (≥ 8Ω) between the pins on JP5 and another
load between the pins on JP3.
Apply power. Make measurements. Plug in a pair of head-
phones. Enjoy.
Introduction
To help the user investigate and evaluate the LM4681's
performance and capabilities, a fully populated demonstra-
tion board is available from the Audio Products Group. This
board is shown in Figure 1. Connected to an external power
supply, a signal source and an I
source), the LM4681 demonstration board easily demon-
2
C signal
strates the amplifier's features.
FIGURE 1. The LM4681 Demonstration Board
AN201959
2
C or SPI controller (or signal
20195901
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Summary of Contents for National Semiconductor LM4681

  • Page 1: Quick Start Guide

    1.” Introduction Apply a 3.0V to 5.0V power supply’s positive voltage output To help the user investigate and evaluate the LM4681’s to the “I2CVDD” pin on jumper JP6. Apply the power supply’s performance and capabilities, a fully populated demonstra- ground return to the “GND“ pin on JP6.

  • Page 2: General Description

    General Description Board Features The LM4681 is a Class D audio amplifier with an internal, The LM4681 demonstration board has all of the necessary digitally controlled volume control, and Class AB stereo connections, using 100mil headers, to apply the power sup- headphone amplifier.
  • Page 3 www.national.com...

  • Page 4: Power Supply Sequencing

    Connections Connecting to the world is accomplished through the 100mil headers on the LM4681 demonstration board. The functions of the different headers are detailed in Table 1. TABLE 1. LM4681 Demonstration Board Connections Jumper Designation Function or Use Power supply connection. Connect an external power supply’s positive voltage source to the JP1 pin labeled “VDD”...

  • Page 5: Pcb Layout Guidelines

    Figure 3. should note that these are only "rule-of-thumb" recommen- The DEFAULT button is used to return the LM4681 to its dations and the actual results are predicated on the final power-on reset state (minimum volume setting, mute on, and layout.

  • Page 6: Bill Of Materials

    Bill of Materials Designator Description Package Value * Notes Polarized Capacitor (Surface Mount) CC3225–1210 (Surface Mount) 10µF 25V, Tantalum Polarized Capacitor (Surface Mount) CC2012–0805 (Surface Mount) 1.0µF 10V, Tantalum Polarized Capacitor (Surface Mount) CC2012–0805 (Surface Mount) 1.0µF 10V, Tantalum Polarized Capacitor (Surface Mount) CC4532–1812 (Surface Mount) 100µF 10V, Tantalum...
  • Page 7 Figure 6 is the upper inner layer. Figure 7 is the lower inner Figures 4 through 8 show the different layers used to create layer. Figure 8 is the bottom layer. the LM4681 four-layer demonstration board. Figure 4 is the 20195909 Figure 4. Top Silkscreen (Shown 2.6X actual size) 20195910 Figure 5.
  • Page 8 Demonstration Board PCB Layout (Continued) 20195911 Figure 6. Upper Middle Layer (Shown 2.6X actual size) 20195912 Figure 7. Lower Middle Layer (Shown 2.6X actual size) www.national.com...
  • Page 9 Demonstration Board PCB Layout (Continued) 20195913 Figure 8. Bottom Layer (Shown 2.6X actual size) www.national.com...
  • Page 10 Typical Demonstration Board Audio Performance (C-CUPL Mode) Typical Class D power amplifier and Class AB headphone amplifier THD+N versus Output Power performance curves at V 12V, are shown in Figure 9 and Figure 10, respectively. Typical Class D power amplifier and Class AB headphone amplifier mode THD+N versus Frequency performance curves at V = 12V are shown in Figure 11 and Figure 12, respectively.
  • Page 11 Appendix A LM4681 I C/SPI Control Register Table A1 shows the actions that are implemented by manipulating the bits within the two internal I C control registers. Table A1. LM4681 I C/SPI Control Register Addressing and Data Format Chart Address...
  • Page 12 Appendix C LLP Package, PCB, Layout, and Mounting Considerations Refer to Application Notes (AN-1187) for more information on Leadless Leadframe Package (LLP). Since National Semiconductor is constantly pursuing the best package performance possible, please refer to the following web <...

  • Page 13: Revision History

    BANNED SUBSTANCE COMPLIANCE National Semiconductor follows the provisions of the Product Stewardship Guide for Customers (CSP-9-111C2) and Banned Substances and Materials of Interest Specification (CSP-9-111S2) for regulatory environmental compliance. Details may be found at: www.national.com/quality/green.

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