EUA4996
Proper Selection of External Components
Gain-Setting Resistor Selection
The input resistor (RI) can be selected to set the gain of
the amplifier according to equation2.
The value of CI is important to consider as it directly
affects the bass (low frequency) performance of the
circuit.
Consider the example where RI is 10kꢀ and the
specification calls for a flat bass response down to 100Hz.
Equation 3 is reconfigured as equation4.
Gain=RF/RI
(2)
1
The internal feedback resistors (RF) are trimmed to
C =
(4)
I
2π R f
40kꢀ.
I C
Resistor matching is very important in fully differential
amplifiers. The balance of the output on the reference
voltage depends on matched ratios of the resistors.
CMRR, PSRR, and the cancellation of the second
harmonic distortion diminishes if resistor mismatch
occurs. Therefore, it is recommended to use 1%
tolerance resistors or better to keep the performance
optimized.
In this example, CI is 0.16µF, so one would likely choose
a value in the range of 0.22µF to 0.47µF.
Ceramic capacitors should be used when possible, as they
are the best choice in preventing leakage current. 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. It is important to
confirm the capacitor polarity in the application.
Bypass Capacitors (CBYPASS) and Start-up Time
The internal voltage divider at the Bypass pin of this
device sets a mid-supply voltage for internal references
and sets the output common mode voltage to VDD/2.
Adding a capacitor to this pin filters any noise into this
pin and increases kSVR. C(BYPASS) also determines the rise
time of VO+ and VO- when the device is taken out of
shutdown. The larger the capacitor, the slower the rise
time. IF Bypass Capacitors are used, it is necessary to
use separate bypass capacitors for each bypass pin.
Decoupling Capacitor (CS)
The EUA4996 is a high-performance CMOS audio
amplifier that requires adequate power supply decoupling
to ensure the output total harmonic distortion (THD) is as
low as possible. Power supply decoupling also prevents
oscillations for long lead lengths between the amplifier
and the speaker. For higher frequency transients, spikes,
or digital hash on the line,
a
good low
equivalent-series-resistance (ESR) ceramic capacitor,
typically 0.1µF to 1 µF, placed as close as possible to the
device VDD lead works best. For filtering lower frequency
noise signals, a 10-µF or greater capacitor placed near the
audio power amplifier also helps, but is not required in
most applications because of the high PSRR of this
device.
Input Capacitor (CI)
The EUA4996 does not require input coupling
capacitors if using a differential input source that is
biased from 0.5V to VDD -0.8V. Use 1% tolerance or
better gain-setting resistors if not using input coupling
capacitors.
Each VDD pin must have a separate power supply
decoupling capacitor. Additionally, the left and high
channel VDD pins must be tied together on the PCB.
In the single-ended input application an input capacitor,
CI, is required to allow the amplifier to bias the input
signal to the proper dc level. In this case, CI and RI form
a high-pass filter with the corner frequency determined
in equation3.
1
f
=
(3)
C
2π R C
I I
DS4996 Ver0.1 July 2008
11
EUTECH [ EUTECH MICROELECTRONICS INC ]
