EUA4890 datasheet(12/14 Pages) EUTECH

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EUA4890

DS4890 Ver 1.7 Dec. 2006

Application Information

Bridged Configuration Explanation

The structure of the EUA4890 is basically composed of

two identical internal power amplifiers; the first one si

externally configurable with gain-setting resistors Rin and

Rf (the closed-loop gain is fixed by the ratios of theses

resistors) and the second is internally fixed in an inverting

unity-gain configuration by two resistors of 20kΩ. So the

load is driven differentially through OUTA and OUTB

outputs. This configuration eliminates the need for an

output coupling capacitor.

The differential-ended amplifier presents two major

advantages:

The possible output power is four times larger (the

output swing is doubled) as compared to single-ended

amplifier under the same conditions.

Output pins (OUTA and OUTB) are biased at the

same potential VDD/2, this eliminates the need for an

output

coupling

capacitor

required

with

single-ended amplifier configuration.

The differential closed loop-gain of the amplifier is

given by Avd=

Power Dissipation

Power dissipation is a major concern when designing a

successful amplifier, whether the amplifier is bridged or

single-ended. A direct consequence of the increased

power delivered to the load by a bridge amplifier is an

increase in internal power dissipation. Since the

EUA4890 has two operational amplifiers in one package,

the maximum internal power dissipation is 4 times that of

a single-ended amplifier. The maximum power dissipation

for a given application can be derived from the power

dissipation graphs of from equation1.

------------(1)

It is critical that the maximum junction temperature TJMAX

of 150°C is not exceeded. TJMAX can be determine from

the power derating curves by using PDMAX and the PC

board foil area. By adding additional copper foil, the

thermal resistance of the application can be reduced,

resulting in higher PDMAX. Additional copper foil can be

added to any of the leads connected to the EUA4890.If

TJMAX still exceeds 150°C, then additional changes must

be made. These changes can include reduced supply

voltage, higher load impedance, or reduced ambient

temperature. Internal power dissipation is a function of

output power.

Proper Selection of External Components

The EUA4890 is unity-gain stable and requires no

external components besides gain-setting resistors, and

input coupling capacitor and proper bypassing capacitor

in the typical application.

Gain-Setting Resistor Selection (Rin and Rf)

Rin and Rf set the closed-loop gain of the amplifier.

In order to optimize device and system performance, the

EUA4890 should be used in low gain configurations.

The low gain configuration minimizes THD + noise

values and maximizes the signal to noise ratio, and the

amplifier can still be used without running into the

bandwidth limitations. Low gain configurations require

large input signals to obtain a given output power. Input

signals equal to or greater than 1Vrms are available from

sources such as audio codecs.

A closed loop gain in the range from 2 to 5 is

recommended to optimize overall system performance.

An input resistor (Rin) value of 20kΩ is realistic in most

of applications, and does not require the use of a too large

capacitor Cin.

Input Capacitor Selection (Cin)

The input coupling capacitor blocks the DC voltage at the

amplifier input terminal. This capacitor creates a

high-pass filter with Rin, the cut-off frequency is given by

The size of the capacitor must be large enough to couple

in low frequencies without severe attenuation. However a

large input coupling capacitor requires more time to reach

its quiescent DC voltage (VDD/2) and can increase the

turn-on pops.

An input capacitor value between 0.1µ and 0.39µF

performs well in many applications (with Rin=22kΩ).

Bypass Capacitor Selection (Cby)

The bypass capacitor Cby provides half-supply filtering

and determines how fast the EUA4890 turns on.

This capacitor is critical component to minimize the

turn-on pop. A 1.0µF bypass capacitor value (Cin=＜

0.39µF) should produce clickless and popless shutdown

transitions. The amplifier is still functional with a 0.1µF

capacitor value but is more susceptible to pop and click

noise. Thus, a 1.0µF bypassing capacitor is recommended.

Power Supply Bypassing (CS)

As with any amplifier, proper supply bypassing is critical

for low noise performance and high power supply

rejection. The capacitor location on both the bypass and

power supply pins should be as close to the device is

possible.

)

/(2π

)

DMAX

Vinrms

Vorms

∏

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