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IS31AP2005-DLS2-TR

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P19
IS31AP2005
Integrated Silicon Solution, Inc. – www.issi.com 10
Rev. C, 08/31/2015
APPLICATION INFORMATION
FULLY DIFFERENTIAL AMPLIFIER
The IS31AP2005 is a fully differential amplifier with
differential inputs and outputs. The fully differential
amplifier consists of a differential amplifier and a
common-mode amplifier. The differential amplifier
ensures that the amplifier outputs a differential voltage
on the output that is equal to the differential input times
the gain. The common-mode feedback ensures that
the common-mode voltage at the output is biased
around V
CC
/2 regardless of the common-mode voltage
at the input. The fully differential IS31AP2005 can still
be used with a single-ended input; however, the
IS31AP2005 should be used with differential inputs
when in a noisy environment, like a wireless handset,
to ensure maximum noise rejection.
ADVANTAGES OF FULLY DIFFERENTIAL
AMPLIFIERS
The fully differential amplifier does not require a
bypass capacitor. This is because any shift in the
midsupply affects both positive and negative channels
equally and cancels at the differential output.
GSM handsets save power by turning on and shutting
off the RF transmitter at a rate of 217Hz. The
transmitted signal is picked-up on input and output
traces. The fully differential amplifier cancels the signal
much better than the typical audio amplifier.
COMPONENT SELECTION
Figure 12 shows the IS31AP2005 with differential
inputs and optional input capacitors. Input capacitors
are used when the common mode input voltage range
specs can not be guaranteed or high pass filter is
considered.
Figure 13 shows the IS31AP2005 with single-ended
inputs. The input capacitors have to be used in the
single ended case because it is much more
susceptible to noise in this case.
OUT+
GND
IS31AP2005
6
8
5
VCC
OUT-
C
S
1 F
VBattery
4
IN-
IN+
3
0.1 F
7
SDB
1
100k
CIN+
0.1 F
C
IN-
0.1 F
R
IN+
150k
RIN-
150k
Differential
Input
Shutdown
Control
Figure 12 Typical Application Circuit with Differential Input
OUT+
GND
IS31AP2005
VCC
OUT-
C
S
1 F
VBattery
IN-
IN+
0.1 F
SDB
100k
CIN-
0.1 F
C
IN+
0.1 F
R
IN-
150k
RIN+
150k
Shutdown
Control
Single-ended
Input
6
8
5
4
3
7
1
Figure 13 Typical Application Circuit with Single-Ended Input
INPUT RESISTORS (R
IN
)
The input resistors (R
IN
) set the gain of the amplifier
according to Equation (1).
IN
R
ain
0k512
G
V
V
(1)
Resistor matching is very important in fully differential
amplifiers. The balance of the output on the reference
voltage depends on matched ratios of the resistors.
CMRR, PSRR, and cancellation of the second
harmonic distortion diminish if resistor mismatch
occurs. Therefore, it is recommended to use 1%
accuracy resistors or better to keep the performance
optimized. Matching is more important than overall
accuracy.
Place the input resistors close to the IS31AP2005 to
reduce noise injection on the high-impedance nodes.
For optimal performance the gain should be set to
2V/V or lower. Lower gain allows the IS31AP2005 to
operate at its best, and keeps a high voltage at the
input making the inputs less susceptible to noise.
DECOUPLING CAPACITOR (C
S
)
The IS31AP2005 is a high-performance Class-D audio
amplifier that requires adequate power supply
decoupling to ensure high efficiency and low total
harmonic distortion (THD). For higher frequency
transients, spikes, or digital noises on the line, a good
low equivalent-series-resistance (ESR) ceramic
capacitor, typically 1μF, placed as close as possible to
the device V
CC
pin works best. Placing this decoupling
capacitor close to the IS31AP2005 is also important for
the efficiency of the Class-D amplifier, because any
resistance or inductance in the trace between the
device and the capacitor can cause a loss in efficiency.
For filtering lower-frequency noise signals, a 10μF or
greater capacitor placed near the audio power
amplifier would also be helpful, but it is not required in
most applications because of better PSRR of this
device.
IS31AP2005
Integrated Silicon Solution, Inc. – www.issi.com 11
Rev. C, 08/31/2015
INPUT CAPACITORS (C
IN
)
The input capacitors and input resistors form a
high-pass filter with the corner frequency, f
C
,
determined in Equation (2).
ININ
CR
c
f
2
1
(2)
The value of the input capacitor is important to
consider as it directly affects the bass (low frequency)
performance of the circuit. Speakers in wireless
phones cannot usually respond well to low frequencies,
so the corner frequency can be set to block low
frequencies in this application.
Equation (3) is reconfigured to solve for the input
coupling capacitance.
CIN
fR
IN
C
2
1
(3)
If the corner frequency is within the audio band, the
capacitors should have a tolerance of ±10% or better,
because any mismatch in capacitance causes an
impedance mismatch at the corner frequency and
below.
For a flat low-frequency response, use large input
coupling capacitors (1μF). However, in a GSM phone
the ground signal is fluctuating at 217Hz, but the signal
from the codec does not have the same 217Hz
fluctuation. The difference between the two signals is
amplified, sent to the speaker, and heard as a 217Hz
hum.
SUMMING INPUT SIGNALS
Most wireless phones or PDAs need to sum signals at
the audio power amplifier or just have two signal
sources that need separate gain. The IS31AP2005
makes it easy to sum signals or use separate signal
sources with different gains. Many phones now use the
same speaker for the earpiece and ringer, where the
wireless phone would require a much lower gain for
the phone earpiece than for the ringer. PDAs and
phones that have stereo headphones require summing
of the right and left channels to output the stereo signal
to the mono speaker.
SUMMING TWO DIFFERENTIAL INPUT SIGNALS
Two extra resistors are needed for summing
differential signals (Figure 14). The gain for each input
source can be set independently by Equations (4) and
(5).
1
1
1502
1
IN
IN
O
R
k
Gain
V
V
V
V
(4)
2
2
1502
2
IN
IN
O
R
k
Gain
V
V
V
V
(5)
Figure 14 Application Circuit with Summing Two Differential Inputs
If summing left and right inputs with a gain of 1V/V, use
R
IN1
= R
IN2
= 300kΩ.
If summing a ring tone and a phone signal, set the
ring-tone gain to Gain2 = 2V/V, and the phone gain to
Gain1 = 0.1V/V. The resistor values would be.
R
IN1
= 3MΩ, and R
IN2
= 150kΩ.
SUMMING A DIFFERENTIAL INPUT SIGNAL AND A
SINGLE-ENDED INPUT SIGNAL
Figure 15 shows how to sum a differential input signal
and a single-ended input signal. Ground noise may
couple in through IN- with this method. It is better to
use differential inputs. The corner frequency of the
single-ended input is set by C
IN2
, shown in Equation (6).
To assure that each input is balanced, the
single-ended input must be driven by a low-impedance
source even if the input is not in use. The gain for each
input source can be set independently by Equations (4)
and (5).
22
2
2
1
CIN
IN
fR
C
(6)
If summing a ring tone and phone signals, the phone
signals should use the differential inputs while the ring
tone should use the single-ended input. The phone
gain is set at Gain1 = 0.1V/V, and the ring-tone gain is
set to Gain2 = 2V/V, the resistor values would be
R
IN1
= 3MΩ, and R
IN2
= 150kΩ.
The high pass corner frequency of the single-ended
input is set by C
IN2
. If the desired corner frequency is
less than 20Hz.
Hzk
IN
C
201502
1
2
(7)
pFC
IN
53
2
(8)
IS31AP2005
Integrated Silicon Solution, Inc. – www.issi.com 12
Rev. C, 08/31/2015
Figure 15 Application Circuit with Summing Differential Input and
Single-Ended Input Signals
SUMMING TWO SINGLE-ENDED INPUT SIGNALS
The corner frequencies (f
C1
and f
C2
) for each input
source can be set independently by Equations (9) and
(10). Resistor, R
P
, and capacitor, C
P
, are needed on
the IN+ terminal to match the impedance on the IN-
terminal (Figure 16). The gain for each input source
can be set independently by Equations (4) and (5).
The single-ended inputs must be driven by low
impedance sources.
11
1
2
1
CIN
IN
fR
C
(9)
22
2
2
1
CIN
IN
fR
C
(10)
21 ININP
CCC
(11)
21
21
ININ
ININ
R
R
RR
P
R
(12)
4
IN-
IN+
3
CP
CIN1-
RP
RIN1-
CIN2- RIN2-
Single-ended
Input 1
Single-ended
Input 2
Figure 16 Application Circuit with Summing Two Single-Ended
Inputs
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P19

IS31AP2005-DLS2-TR

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Manufacturer:
ISSI
Description:
Audio Amplifiers 2.7W Audio Pwr Amp
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