IS31AP4913
Integrated Silicon Solution, Inc. – www.issi.com 8
Rev. C, 12/25/2013
APPLICATION INFORMATION
GENERAL DESCRIPTION
The IS31AP4913 is a high quality stereo headphone
driver with 3D and bass enhancement.
OPERATING MODE
The operating mode is controlled by Pulse Count
Control (PCC wire) serial interface. The interface
records rising edges of the CTRL pin and decodes
them into 4 operating mode (Figure 9).
If the CTRL pin is pulled to high, receiving one rising
edge, the IC starts up and operates in Mode 1. If the
CTRL pin receives two rising edges, the IC operates in
Mode 2. If the CTRL pin receives three rising edges,
the IC operates in Mode 3. If the CTRL pin receives
four rising edges, the IC operates in Mode 4.
Mode 1—IC starts up, basic operating mode.
Mode 2—IC starts up, enable 3D enhance function.
Mode 3—IC starts up, enable bass enhance function.
Mode 4—IC starts up, enable 3D and bass enhance
function.
If the CTRL pin is pulled to low last at least 200µs, the
IC will be into shutdown mode.
Figure 9 Operating Mode Selected
CHARGE PUMP CONVERTER
IS31AP4913 integrates a charge pump converter to
change input supply voltage (VCC) into a negative
voltage providing a 0V reference for the output.
The charge pump converter only needs three external
components: supply decoupling capacitor, output
bypass capacitor and flying capacitor.
Choose low ESR capacitors to ensure the best
operating performance and place the capacitors as
close as possible to the IS31AP4913.
GAIN SETTING
The input resistors (R
IN
) and feedback resistors (R
F
)
set the gain of the amplifier according to Equation (1).
IN
F
R
R
ain G
V
V
(1)
The R
F
is given by Equation (2) below:
321
321
FFF
FFF
F
RRR
RRR
R
(2)
For example, in Figure 1:
R
F1
= 20k, R
F2
= 20k, R
F3
= 120k, R
IN
= 30k,
therefore,
k
F
R 30
1202020
1202020
1G
30
30
ain
V
V
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%
tolerance resistors or better to keep the performance
optimized. Matching is more important than overall
tolerance. Resistor arrays with 1% matching can be
used with a tolerance greater than 1%.
Place the input resistors very close to the IS31AP4913
to limit noise injection on the high-impedance nodes.
BASS AUDIO ENHANCEMENT EFFECT
When the bass enhancement is enabled, the low
frequency input signal will be amplified (Figure 8). The
cutoff frequency is f
B
. The signal below f
B
will be
enhanced. f
B
is given by Equation (3):
BFF
B
CRR
f
21
2
1
(3)
For example, in Figure 1:
R
F1
= 20k, R
F2
= 20k, C
B
= 22nF,
so,
Hzf
nFkk
B
181
2220202
1
The capacitors should have a tolerance of ±10% or
better, because any mismatch in capacitance causes
an impedance mismatch at the startup frequency and
below.
