EUA4996
Application Information
Fully Differential Amplifier
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 EUA4996. 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.
The EUA4996 is a fully differential amplifier that
features differential inputs and outputs. The EUA4996
also includes a common mode feedback loop that
controls the output bias value to average it at VCC/2 for
any DC common mode input voltage. This allows the
device to always have a maximum output voltage swing,
and by consequence, maximize the output power.
Moreover, as the load is connected differentially,
compared to a single-ended topology, the output is four
times higher for the same power supply voltage. The
fully differential EUA4996 can still be used with a
single-ended input; however, the EUA4996 should be
used with differential inputs when in
environment, like wireless handset, to ensure
maximum noise rejection.
a noisy
a
Advantages of Fully Differential Amplifiers
The advantages of a full-differential amplifier are:
z Very high PSRR (Power Supply Rejection Ratio).
z High common mode noise rejection.
z Virtually zero pop without additional circuitry,
giving an faster start-up time compared to conventional
single-ended input amplifiers.
z No input coupling capacitors required thanks to
common mode feedback loop.
z Midsupply bypass capacitor not required.
Application Schematics
Figure 26 through Figure 27 show application
schematics for differential and single-ended inputs.
Typical values are shown in Table1.
Figure 26.Differential Input Application Schematic
Optimized with Input Capacitors
Table1. Typical Component Value
Component
Value
40kꢀ
0.22µF
1µF
RI
C(BYPASS)
CS
CI
0.22µF
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. The maximum
power dissipation for a given application can be derived
from the power dissipation graphs of from equation1.
P
= 4*(V )2 /(2π2R )
------------(1)
DD L
DMAX
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
Figure 27.Single-Ended Input Application Schematic
DS4996 Ver0.1 July 2008
10
EUTECH [ EUTECH MICROELECTRONICS INC ]
