AS1701_1 AMSCO [austriamicrosystems AG], AS1701_1 Datasheet - Page 13

• Manufacturer Part Number: AS1701_1
• Description: 1.6W Audio Power Amplifiers
• Manufacturer: AMSCO [austriamicrosystems AG]

AS1701, AS1706
Data Sheet
Input Filter
Input capacitor C
ing signal. C
3dB point of the high-pass filter is given by:
Select the value for R
well below the lowest frequency of interest. Setting f
Capacitors with dielectrics that have low-voltage coefficients such as tantalum or aluminum electrolytic should be used,
since capacitors with high-voltage coefficients, such as ceramics, can increase distortion at low frequencies.
Note: Other considerations when designing the input filter include the overall constraints of the system, the frequency
Bias Bypass Capacitor
The bias bypass capacitor, C
bias node, and serves as the primary click- and pop-suppression component. C
source, and controls the rate at which the common-mode bias voltage rises at power-up and falls during shutdown. For
optimal click- and pop-suppression, ensure that the input capacitor (C
C
The value of C
Note: A larger C
Click- and Pop-Less Operation
AC-coupling capacitors (C
C
On power-up, C
ates a voltage transient at the amplifier output, which can result in an audible pop. Minimizing the value of C
this effect, optimizing click-and-pop suppression.
For more information see
Supply Bypassing
Proper power supply bypassing – connect a 0.1µF ceramic capacitor in parallel with a 10µF ceramic capacitor from
V
added as required.
Note: Place the capacitors as close to the device as possible.
Volume Control
The addition of a digital potentiometer (AS1500 family) used as an input attenuator, can provide simple volume control
for the AS1701/AS1706.
Connect the high terminal of the AS150x to the audio input, the low terminal to ground and the AS150x wiper to C
shown in
lowest position fully attenuates the input.
www.austriamicrosystems.com
DD
BIAS
BIAS
to GND – will ensure low-noise, low-distortion performance of the device. Additional bulk capacitance can be
.
determines the rate at which the mid-rail bias voltage rises on power-up and falls when entering shutdown.
band of interest, and click-and-pop suppression. Although hi-fi audio specifies a flat gain response between
20Hz and 20kHz, portable voice reproduction devices such as mobile phones and two-way radios only need
address the frequency range of the human voice (~ 300Hz to 3.5kHz). Additionally, speakers used in portable
devices typically have poor response below 150Hz. In practice, the input filter may not need to be designed for
the 20Hz to 20kHz range, which could save PCB space and design costs since only small capacitors would be
required.
Figure
IN
- A p p l i c a t i o n I n f o r m a t i o n
BIAS
allows the amplifier to bias the signal to an optimum DC level. Assuming zero source impedance, the -
IN
31). Setting the wiper to the top position passes the audio signal unattenuated; setting the wiper to the
IN
BIAS
is charged to its quiescent DC voltage through the R
(if used), in conjunction with R
for best click- and pop-suppression is given by:
IN
value yields higher PSRR.
as specified in
Bias on page 10
IN
) along with C
BIAS
, improves PSRR and THD+N by reducing power supply noise at the common-mode
Gain-Setting Resistors on page
BIAS
and
facilitate click- and pop-less power-up and shutdown. The value of
Bias Bypass Capacitor on page
C
BIAS
IN
, forms a high-pass filter that removes the DC bias from an incom-
-3dB
f
Revision 1.52
-3dB
≤
10
too high can affect the low-frequency response of the device.
=
2
C
25kΩ
π
IN
R
R
1
IN
IN
C
IN
IN
F
12. Choose the value for C
) is fully charged (ten time constants) before
from the output. The current generated cre-
BIAS
13.
is fed from an internal 25k Ω
IN
such that f
IN
reduces
(EQ 12)
(EQ 13)
-3dB
13 - 17
IN
(as
is