EUA6412 datasheet(13/18 Pages) EUTECH

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EUA6412

DS6412 Ver 1.0 Dec. 2006

Application Information

Gain Setting

The gain of the EUA6412 is set by two input terminals,

Gain0 and Gain1.The gains listed in Table 1 are realized

by changing the taps on the input resistors inside the

amplifier.

Table 1.Gain Setting

GAIN0

GAIN1

BTL

SE/

AV(inv)

6dB

90kΩ

10dB

70kΩ

15.6dB

45kΩ

21.6dB

25kΩ

4.1dB

Input Resistance

Each gain setting is achieved by varying the input

resistance of the amplifier, which can range from its

smallest value to over 6 times that value. As a results, if a

single capacitor is used in the input high pass filter,

the –3 dB or cut off frequency will also change by over 6

times. If an additional resistor is connected from the input

pin of the amplifier to ground, as shown in the figure

below, the variation of the cut-off frequency will be much

reduced.

The-3dB frequency can be calculated using

equation 1:

f-3dB =

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

If the filter must be more accurate, the value of the

capacitor should be increased while the value of the

resistor to ground should be decreased. In addition, the

order of the filter could be increased.

Input Capacitor, Ci

In the typical application an input capacitor, Ci, is

required to allow the amplifier to bias the input signal to

the proper dc level for optimum operation. In this case, Ci

and the input impedance of the amplifier, Zi, from a

high-pass filter with the corner frequency determined in

equation 2.

fc(highpass)=

-----------------(2)

The value of Ci is important to consider as it directly

affects the bass (low frequency) performance of the

circuit. Consider the example where Zi is 710kΩ and the

specification calls for a flat bass response down to 40Hz.

Equation 2 is reconfigured as equation 3.

Ci =

----------------------------- (3 )

In this example, Ci is 5.6nF so one would likely choose a

value in the range of 5.6nF to 1µF. A further

consideration for this capacitor is the leakage path from

the input source through the input network (Ci) and the

feedback network to the load. This leakage current

creates a dc offset voltage at the input to the amplifier

that reduces useful headroom, especially in high gain

applications. For this reason a low- leakage tantalum or

ceramic capacitor is the best choice. When polarized

capacitors are used, the positive side of the capacitor

should face the amplifier input in most applications as

the dc level there is held at VDD/2, which is likely higher

than the source dc level. Note that it is important to

confirm the capacitor polarity in the application.

)

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