EUA6011A Datasheet, PDF (17/20 Pages) Eutech Microelectronics Inc – 3-W Stereo Audio Power Amplifier with Advanced DC Volume Control

SE/BTL Operation
The ability of the EUA6011A to easily switch between
BTL and SE modes is one of its most important cost
saving features. This feature eliminates the requirement
for an additional headphone amplifier in applications
where internal stereo speakers are driven in BTL mode but
external headphone or speakers must be accommodated.
Internal to the EUA6011A , two separate amplifiers drive
OUT+ and OUT- .The SE/BTL input (terminal 15)
control the operation of the follower amplifier that drives
LOUT- and ROUT- (terminals 9 and 16).When
SE/BTL is held low, the amplifier is on and the
EUA6011A is in the BTL mode. When SE/BTL is held
high, the OUT- amplifiers are in a high output impedance
state, which configures the EUA6011A as an SE driver
from LOUT+ and ROUT+ (terminals 4 and 21). I_DD is
reduced by approximately one-half in SE mode. Control
of the SE/BTL input can be from a logic-level CMOS
source or, more typically, from a resistor divider network
as shown in Figure 30.
EUA6011A
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.
Figure 31. Input Resistor
The-3dB frequency can be calculated using equation
3:
1
f_-3dB = _{2 π C (R || R i )}
-------------- (3)
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.
Figure 30. Resistor divider Network circuit 2
Using a readily available 1/8-in. (3.5mm) stereo headphone
jack, the control switch is closed when no plug is inserted.
When closed the 100-kΩ /1-kΩ divider pulls the
SE/BTL input low. When a plug is inserted, the 1-kΩ
resistor is disconnected and the SE/BTL input is pulled
high. When the input goes high, the OUT- amplifier is shut
down causing the speaker to mute(virtually open-circuits
the speaker).The OUT+ amplifier then drives through the
output capacitor (C_O) into the headphone jack.
Input Capacitor, C_i
In the typical application an input capacitor, C_i, is required
to allow the amplifier to bias the input signal to the proper
dc level for optimum operation. In this case, C_i and the input
impedance of the amplifier, Z_i, from a high-pass filter with
the corner frequency determined in equation 4.
fc(highpass)=
1 _{-----------------(4)}
2π Z_iC_i
The value of C_i is important to consider as it directly affects
the bass (low frequency) performance of the circuit.
Consider the example where Z_i is 70kΩ and the
specification calls for a flat bass response down to 40Hz.
Equation 2 is reconfigured as equation 5.
C_i =
1
----------------------------(5 )
2π Z_if_C
DS6011A Ver 1.0 Mar. 2006
17