LM4802B, LM4802BLQBD

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SNAS243C – MAY 2004 – REVISED MARCH 2005

For the LQA28A,

the system surroundings, Equation 5 can be used to find the maximum internal power dissipation supported by

the IC packaging. If the result of Equation 4 is greater than that of Equation 5, then either the supply voltage

supply, with V1 set to 5.8V and a 2uF+30

Ω load, the maximum ambient temperature possible without violating

the maximum junction temperature is approximately 116°C provided that device operation is around the

maximum power dissipation point. Thus, for typical applications, power dissipation is not an issue. Power

dissipation is a function of output power and thus, if typical operation is not around the maximum power

dissipation point, the ambient temperature may be increased accordingly. Refer to the Typical Performance

Characteristics curves for power dissipation information for lower output levels.

EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS

The LM4802’s exposed-DAP (die attach paddle) package (LD) provides a low thermal resistance between the

die and the PCB to which the part is mounted and soldered. The low thermal resistance allows rapid heat

transfer from the die to the surrounding PCB copper traces, ground plane, and surrounding air. The LD package

should have its DAP soldered to a copper pad on the PCB. The DAP’s PCB copper pad may be connected to a

large plane of continuous unbroken copper. This plane forms a thermal mass, heat sink, and radiation area.

Further detailed and specific information concerning PCB layout, fabrication, and mounting an LD (LLP) package

is found in Texas Instruments' Package Engineering Group under application note AN1187.

SHUTDOWN FUNCTION

In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry to

provide a quick, smooth transition into shutdown. Another solution is to use a single-pole, single-throw switch,

and a pull-up resistor. One terminal of the switch is connected to GND. The other side is connected to the two

guarantees that the shutdown pins will not float thus preventing unwanted state changes.

PROPER SELECTION OF EXTERNAL COMPONENTS

Proper selection of external components in applications using integrated power amplifiers, and switching DC-DC

converters, is critical for optimizing device and system performance. Consideration to component values must be

used to maximize overall system quality.

The best capacitors for use with the switching converter portion of the LM4802 are multi-layer ceramic

capacitors. They have the lowest ESR (equivalent series resistance) and highest resonance frequency, which

makes them optimum for high frequency switching converters.

When selecting a ceramic capacitor, only X5R and X7R dielectric types should be used. Other types such as

Z5U and Y5F have such severe loss of capacitance due to effects of temperature variation and applied voltage,

they may provide as little as 20% of rated capacitance in many typical applications. Always consult capacitor

manufacturer’s data curves before selecting a capacitor. High-quality ceramic capacitors can be obtained from

Taiyo-Yuden, AVX, and Murata.

POWER SUPPLY BYPASSING

As with any amplifier, proper supply bypassing is critical for low noise performance and high power supply

SELECTING INPUT CAPACITOR FOR AUDIO AMPLIFIER

One of the major considerations is the closedloop bandwidth of the amplifier. To a large extent, the bandwidth is

order high pass filter which limits low frequency response. This value should be chosen based on needed

frequency response for a few distinct reasons.

High value input capacitors are both expensive and space hungry in portable designs. Clearly, a certain value

capacitor is needed to couple in low frequencies without severe attenuation. But ceramic speakers used in

portable systems, whether internal or external, have little ability to reproduce signals below 100Hz to 150Hz.

Thus, using a high value input capacitor may not increase actual system performance.

Copyright © 2004–2005, Texas Instruments Incorporated

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