IS31AP2145A
Integrated Silicon Solution, Inc. – www.issi.com 10
Rev.A, 11/20/2011
The attack time and the release time of AGC control
have two levels (refer to Table 1). They are selected by
the voltage at the CTRL terminal (refer to Table 2). The
attack time is a time interval that gain falls from 18dB
to 10dB with a big signal input enough. And the release
time is a time from target attenuation to no AGC
attenuation.
Table 1 Attack Time and Release Time
AGC Mode Attack Time Release Time
AGC1
(Recommended)
45ms 2.6s
AGC2 10ms 1.2s
Assuming no limitation by the power supply, the audio
output signal would be as in Figure 15.
Figure 15 Assuming no Restriction from Power Supply, the Audio
Output Signal
In normal operation without the AGC, the output is
distorted because of the restriction from power supply,
as shown in Figure 16.
Figure 16 AGC Function Off
With the AGC function of IS31AP2145A, the optimum
output power can be obtained along with the minimal
distortion. The Figure 17 shows the outcome of AGC
function.
Attack Time Release Time
Figure 17 AGC Function On
CTRL TERMINAL FUNCTION
By setting the threshold voltage of each mode to CTRL
terminal, the followings can be set: AGC1, AGC2, AGC
OFF, and Shutdown Mode (Table 2 and Figure 18).
Figure 18 AGC Function Mode Setting
Table 2 Mode Setting
CTRL1 CTRL2 Mode
H H AGC1
H GND AGC2
GND H AGC OFF
GND GND Shutdown
“H” level indicates a microcomputer’s I/O port H level
output voltage that is input to CTRL1 and CTRL2
terminals and GND indicates GND of the
microcomputer.
GND level of the microcomputer must be the same as
that of IS31AP2145A.
The control of CTRL terminal is based on I/O port H
level output voltage of microcomputer that is
connected.
Set resistance constants according to I/O port H level
output voltage of each microcomputer as Table 3
below.
Table 3 Resistors Setting
V
I/O
1.8V 2.6V 2.8V 3.0V 3.3V 5.0V
R1 27k 33k 33k 33k 33k 56k
R2 56k 68k 68k 68k 68k 120k
R3 82k 27k 24k 22k 18k 15k
Functions of CTRL pin are designed with their control
by two control pins (CTRL1 and CTRL3). Only a
switching control between AGC1 Mode and Shutdown
Mode is available when a single control terminal is
used (Table 4 and Figure 19).
Figure 19 AGC1 Mode Circuit
Table 4 Mode Setting
CTRL1 Mode
H AGC1
GND Shutdown
SYSTEM TIMING
The CTRL terminal should be configured as the Figure
20. When in the Shutdown Mode, the level of the
terminal must not be changed from GND level during
t
SD
. When the IS31AP2145A wakes up, the CTRL
terminal must be set to H level first, then enter the
setting mode.
