EUA6210
guarantee that the
SHUTDOWN
pin will not float. This
prevents unwanted state changes. In a system with a
microprocessor or microcontroller, use a digital output to
apply the control voltage the
SHUTDOWN
pin. Driving
the
SHUTDOWN
pin with active circuitry eliminates the
pull-up resistor.
Power Dissipation
Power dissipation is a major concern when designing a
successful amplifier. A direct consequence of the
increased power delivered to the load by a bridge
amplifier is an increase in internal power dissipation. The
maximum power dissipation for a given application can
be derived from the power dissipation graphs or from
Equation 1.
In addition to system cost and size, turn-on time is
affected by the size of the input coupling capacitor C
i
. A
larger input coupling capacitor requires more charge to
reach its quiescent DC voltage. This charge comes from
the output via the feedback Thus, by minimizing the
capacitor size based on necessary low frequency response,
turn-on time can be minimized. A small value of C
i
(in the
range of 0.1µF to 0.39µF), is recommended.
Power Supply Bypassing
As with any amplifier, proper supply bypassing is
important for low noise performance and high power
supply rejection. The capacitor location on the power
supply pins should be as close to the device as possible.
Typical applications employ a 3.3V regulator with 10µF
tantalum or electrolytic capacitor and a ceramic bypass
capacitor which aid in supply stability. This does not
eliminate the need for bypassing the supply nodes of the
EUA6210. A bypass capacitor value in the range of
0.1µF to 1µF is recommended for CS.
Using External Powered Speakers
TheEUA6210 is designed specifically for headphone
operation. Often the headphone output of a device will be
used to drive external powered speakers. The EUA6210
has a differential output to eliminate the output coupling
capacitors. The result is a headphone jack sleeve that is
connected to V
O3
instead of GND. For powered speakers
that are designed to have single-ended signals at the input,
the click and pop circuitry will not be able to eliminate the
turn- on/turn-off click and pop. Unless the inputs to the
powered speakers are fully differential the turn-on/
turn-off click and pop will be very large.
ESD Protection
As stated in the Absolute Maximum Ratings, pin 6(V
O
3)
on the EUA6210 has a maximum ESD susceptibility
rating of 8kV. For higher ESD voltages, the addition of a
PCDN042 dual transil (from California Micro Devices),
as shown in Figure 17, will provide additional protection.
P
DMAX
=
4
(
V
DD
)
2
/
π
2
R
L
----------------------------(1)
It is critical that the maximum junction temperature T
JMAX
of 150
℃
is not exceeded. Since the typical application is
for headphone operation (32Ω impedance ) using a 3.3V
supply the maximum power dissipation is only 138mW.
Therefore power dissipation is not a major concern.
Gain-Setting Resistor Selection (R
i
and R
f
)
R
i
and R
f
set the closed-loop gain of the amplifier.
In order to optimize device and system performance, the
EUA6210 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 (R
i
) value of 20kΩ is realistic in most of
applications, and does not require the use of a too large
capacitor C
in
.
Input Capacitor Selection (C
i
)
Amplifiying the lowest audio frequencies requires a high
value input coupling capacitor, C
i
. A high value capacitor
can be expensive and may compromise space efficiency in
portable designs. In many cases, however, the headphones
used in portable systems have little ability to reproduce
signals below 60Hz. Applications using headphones with
this limited frequency response reap little improvement by
using a high value input capacitor.
(
)
Figure 17.
DS6210 Ver1.1 Aug. 2007
9
EUTECH [ EUTECH MICROELECTRONICS INC ]
