apa2070 Anpec Electronics Corporation, apa2070 Datasheet - Page 17

• Manufacturer Part Number: apa2070
• Description: Stereo 2.6w Audio Power Amplifier With Dc Volume Control
• Manufacturer: Anpec Electronics Corporation

Application Information
APA2070
Input Resistance (R
The gain for each audio input of the APA2070 is set by the
internal resistors (R
in inverting configuration.
BTL mode operation brings the factor of 2 in the gain
equation due to the inverting amplifier mirroring the volt-
age swing across the load. For varying gain settings, the
APA2070 generates each input resistance on figure 4.
The input resistance will affect the low frequency perfor-
mance of audio signal. The minmum input resistance is
30k
ramp up when close loop gain below 18dB. The input
resistance has wide variation (+/-10%) caused by pro-
cess variation.
Input Capacitor (C
In the typical application, an input capacitor (C
to allow the amplifier to bias the input signal to the proper
DC level for optimum operation. In this case, C
minimum input impedance R
filter with the corner frequency determined in the follow-
ing equation :
Copyright
Rev. A.2 - Aug., 2008
SE
BTL
F
C
160
140
120
100
when gain setting is 18dB and the resistance will
(
highpass
80
60
40
20
Figure 4: Input resistance vs. Gain setting
Gain
0
Gain
-40
)
ANPEC Electronics Corp.
A
-30
-2
V
2
i
)
R
i
R
i
)
and R
30
F
-20
i
R
R
R
1
i
k
F
i
vs. Gain(BTL)
Gain(BTL)
F
-10
) of volume control amplifier
C
i
i
(30k ) form a high-pass
0
10
i
) is required
20
i
and the
(2)
(3)
(4)
17
The value of C
directly affects the low frequency performance of the circuit.
Consider the example where R
cation calls for a flat bass response down to 50Hz. Equa-
tion is reconfigured below :
The value of C
tion of input resistance (R
the range from 0.047 F to 0.47 F. A further consideration
for this capacitor is the leakage path from the input source
through the input network (R
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 low-leakage
tantalum or ceramic capacitor is the best choice. When
polarized capacitors are used, the positive side of the
capacitor should face the amplifier input in most applica-
tions as the DC level there is held at V
that it is important to confirm the capacitor polarity in
the application.
Effective Bypass Capacitor (C
A power amplifier, proper supply bypassing, is critical
for low noise performance and high power supply
rejection.
The capacitor location on the BYPASS pin should be as
close to the device as possible. The effect of a larger
supply bypass capacitor is to improve PSRR due to
increased half-supply stability. Two critical criteria of
bypass capacitor (C
s i r e d P S R R r e q u i r e m e n t s an d c l i c k - an d - p o p
performance; 2
induce the voltage drop of V
pin), and if the V
will enter mute condition. The value of V
calculated as blew:
Where
I
Therefore, it is recommended that C
rent should be no more than 0.4 A for properly work of
the APA2070.
Leakage
V
i C
BYPASS
=Leakage current of C
2
30
0.5V
i
i
1
k
should be 0.1 F, and consider the varia-
must be considered carefully because it
BYPASS
nd
, the leakage current of C
DD
F
C
I -
BYPASS
is less than 0.49V
Leakage
i
), it’ s better to choose a value in
): 1
BYPASS
BYPASS
i
+R
BYPASS
150k
i
st
is 30k
, it depends upon de-
F
, C
(voltage of BYPASS
BYPASS
)
www.anpec.com.tw
i
) to the load. This
DD
DD
and the specifi-
/2. Please note
’ s leakage cur-
, the APA2070
BYPASS
BYPASS
can be
(
(
5)
6)
will