EUA6205
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 EUA6205. 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.
Selection Components
Resistors (RF and RI)
The input (RI) and feedback resistors (RF) set the gain of
the amplifier according to Equation 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 RI is 10kΩ and the
specification calls for a flat bass response down to 100 Hz.
Equation 2 is reconfigured as Equation 4.
Gain = R /R
----------------------------------------(2)
F
I
1
RF and RI should range from 1kΩ to 100kΩ. Most graphs
were taken with RF=RI=20 kΩ.
C =
-------------------------------- (4)
I
2π R f
I C
Resistor matching is very important in fully differential
amplifiers. The balance of the output on the reference
voltage depends on matched rations of 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. A further
consideration for this capacitor is the leakage path from
the input source through the input network (RI, CI) and the
feedback resistor (RF) 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
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. It is important to confirm the
capacitor polarity in the application.
Bypass Capacitor (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 the 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. Although the
output rise time depends on the bypass capacitor value, the
device passes audio 4 µs after taken out of shutdown and
the gain is slowly ramped up based
Decoupling Capacitor (CS)
The EUA6205 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,
on C(BYPASS)
.
To minimize pops and clicks, design the circuit so the
impedance (resistance and capacitance) detected by both
inputs, IN+ and IN-, is equal.
or digital hash on the line,
a
good low
Input Capacitor (CI)
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.
The EUA6205 does not require input coupling capacitors if
using a differential input source that is biased from 0.5 V to
VDD - 0.8 V. Use 1% tolerance or better gain-setting
resistors if not using input coupling capacitors.
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 Equation 3.
1
f
=
C
2π R C
I I
--------------------------------- (3)
DS6205 Ver 1.0 Mar. 2007
11
EUTECH [ EUTECH MICROELECTRONICS INC ]
