EUA6021A Datasheet, PDF (14/16 Pages) Eutech Microelectronics Inc – 2.5-W Stereo Audio Power Amplifier with Advanced DC Volume Control

SE/BTL Operation
The ability of the EUA6021A 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 EUA6021A , two separate amplifiers drive
OUT+ and OUT- .The SE/BTL input control the
operation of the follower amplifier that drives LOUT- and
ROUT-.When SE/BTL is held low, the amplifier is on and
the EUA6021A is in the BTL mode. When SE/BTL is
held high, the OUT- amplifiers are in a high output
impedance state, which configures the EUA6021A as an
SE driver from LOUT+ and ROUT+. 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 29.
EUA6021A
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 30. 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 29. 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
DS6021A Ver 1.2 Jun. 2007
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.
C_i =
1
----------------------------- (5)
2π Z_if_C
14