Revision 2.1
Page 1 of 27
austria
micro
systems
Key Features
-
Line/speech handsfree circuit, LD/MF repertory dialler,
and tone ringer on one 44 pin CMOS chip
-
Operating range from 15 to 100 mA line current (down
to 5 mA with slightly reduced performance)
-
All significant parameters programmable with external
EEPROM
-
Volume control of receiver signal
-
Handsfree function with enhanced voice switching
-
Low noise (max. -72 dBmp)
-
Unique EMC performance
-
LD/MF switchable dialing with temporary MF mode
-
Repertory dialing with last number redial and memory
dialing (8 x 2 direct and 12 indirect)
-
Call restriction with PIN code
-
Serial interface for EEPROM and LCD driver
-
2-tone/3-tone ringer with ring frequency detection
Package
Available in 44 pin TQFP.
General Description
The AS2525 is a CMOS mixed-mode integrated circuit for
use in feature phones, answering machines and fax
machines. It contains an analogue line interface and
speech circuit for a/b terminals, loudhearing, handsfree,
enhanced LD/MF dialler, tone ringer with dc/dc converter
and serial interface to EEPROM and LCD-driver (AS2591),
all in a 44 pin package. The circuit is fully line powered.
The AS2525 uses an external EEPROM for a 32 digit last
number redial storage and memories for 28 numbers each
containing up to 24 digits/data.
The device provides a volume control for the earpiece and
the loudspeaker. The volume can be controlled by pressing
the [V-]/[V+] keys.
The versatility of the circuit is provided by programming all
parameters through an external EEPROM. This allows easy
adaptation to various PTT requirements worldwide.
Block Diagram
CS
SS
LI
V
PP
LS
+
+
+
+
V
SS
30
RI
STB
300
Z
BAL
A
GND
V
DD
V
DD
V
DD
+
V
PP
V
PP
M1
M2
M3
M4
LO1
LO2
V
SSA
RECI
RECV
RO
NOISE
DET.
LINE
SENSE
PEAK
DET.
VOICE
SWITCHING
PEAK
DET.
DTMF
MELODY
DEBOUNCE
CPU
DIALLER
DC/DC
CONVERTER
OSCILLATOR
KEYSCANNING
CM
KEYBOARD (C1-4/R1-3)
HS
HF
DM/HM
FCI
DPN
LED
DI DO CLK
CS1 CS2
V
SS
CI
SUPPLY
V
REF
V
DD
A
GND
A
GND
FT2
CBN
FT1
AS2525
3.58
MHz
Single-Chip Handsfree Phone
CMOS Integrated Circuit
AS2525
DATA SHEET
Datasheet AS2525
austria
micro
systems
Revision 2.1
Page 2 of 27
Pin Description
Pin #
Symbol
Type
Description
1
CS2
DO
C
hip
S
elect
2
Chip select signal for external LCD driver circuit or 2 mA LED
If signal is not activated, a pull down resistor (100 k
) is inserted.
2
DPn
DO
D
ial
P
ulse Output
Digital output that holds the line during off-hook operation or pulls low during break periods
of pulse dialing and flash.
3
HF
DI
H
ands
F
ree Switch Input
This is a Schmitt-trigger input that is pulled high to enable handsfree operation.
4
HS
DI
H
and
S
et Switch Input
This is a Schmitt-trigger input that is pulled high by the hook switch to enable handset or
headset operation.
5
FT1
AI
Analogue input pin for connecting a capacitor for offset cancellation.
6
FT2
AI
Analogue input pin for connecting a capacitor for offset cancellation.
7
M4
AI
M
icrophone Input
4
Differential input for the handsfree microphone (electret).
8
M2
AI
M
icrophone Input
2
Differential input for the handset microphone (electret).
9
M3
AI
M
icrophone Input
3
Differential input for the handsfree microphone (electret).
10
M1
AI
M
icrophone Input
1
Differential input for the handset microphone (electret).
11
STB
AI
S
ide
T
one
B
alance Input
Analogue input for side tone cancellation network.
12
CS
AO
C
urrent
S
hunt Control Output
N-channel open drain output to control the external high power shunt transistor for
synthesizing ac- and dc-impedance, modulation of line voltage and shorting the line during
make periods of pulse dialing.
13
V
SS
Supply
V
oltage
S
ource
S
ource
Negative Power Supply.
14
LI
AI
L
ine
I
nput
Analogue input used for power extraction and line current sensing.
15
RI
AI
R
eceive
I
nput
Analogue input for ac-separated receive signal.
16
SS
AO
S
upply
S
ource Control Output
N-channel open drain output to control the external high power source transistor for
supplying (Vpp) the loudspeaker amplifier in off-hook loudspeaking/handsfree mode.
17
LS
AI
L
ine Current
S
ense Input
Analogue input for sensing the line current.
18
CI
AI
C
omplex
I
mpedance Input
Analogue input pin for the capacitor to program a complex impedance.
Datasheet AS2525
austria
micro
systems
Revision 2.1
Page 3 of 27
Pin #
Symbol
Type
Description
19
RECI
AI
REC
eive
I
nput
Analogue input for the handsfree receive path. Should be connected to RO via a coupling
capacitor.
20
RECV
AI
REC
eive
V
oice Switching Input
Analogue input for receive voice switching path.
21
RO
AO
R
eceive
O
utput to
H
andset
Output for driving a dynamic earpiece with an impedance from 150
to 300
.
22
V
DD
Supply
V
oltage
D
rain
D
rain
Positive Power Supply.
23
A
GND
Supply
A
nalogue
G
rou
nd
Special ground for the internal amplifiers.
24
CBN
AI
Analogue input pin for connecting a capacitor for background noise monitoring.
25
CM
DO
C
onverter
M
ake Output
This is an output for controlling the external switching converter. During ringing it converts
the ring signal into a 4V supply voltage.
26
V
PP
Supply
Loudspeaker Power Supply
High power supply for the output driver stage.
27
28
LO1
LO2
AO
L
oudspeaker
O
utputs
1/2
Output pins for a 32
( 25 to 50
) loudspeaker.
29
V
SSA
Supply
Power supply pin for LO1-LO2 output amplifier.
30
DM/HM
DI
D
ial
M
ode/
H
eadset
M
ode Switch Input
Digital input for choosing between LD and MF dialing or choosing handset and headset
mode. See "Table 3: Parameter settings" for further details. This pin is scanned after manual
off-hook only.
31
FCI
DI
F
requency
C
omparator
I
nput
This is a Schmitt-trigger input for ring frequency discrimination. Disabled during off-hook.
32
LED
DO
LED
Output
Digital output for connecting 2 mA LED to indicate handsfree mode.
33
OSC
Osc
illator Input
Input for ceramic resonator 3.58 MHz.
34
35
36
R1
R2
R3
DI/O
Keyboard
R
ows
(see Figure 1: Keyboard Layout).
37
38
39
40
C1
C2
C3
C4
DI/O
Keyboard
C
olumns
(see Figure 1: Keyboard Layout).
41
CLK
DO
Cl
oc
k
Clock output for 3-wire bus.
If signal is not activated, a pull down resistor (100 k
) is inserted.
42
DI
DI
D
ata
I
nput
Data input of 3-wire bus.
If signal is not activated, a pull down resistor (100 k
) is inserted.
Datasheet AS2525
austria
micro
systems
Revision 2.1
Page 4 of 27
Pin #
Symbol
Type
Description
43
DO
DO
D
ata
O
utput
Data output of 3-wire bus.
A 100 k
resistor connected from this pin to VSS enables key locking.
If signal is not activated, a pull down resistor (100 k
) is inserted.
44
CS1
DO
C
hip
S
elect
1
Chip select signal for external EEPROM.
If signal is not activated, a pull down resistor (100 k
) is inserted.
DI:
Digital Input
DO:
Digital Output
DI/O:
Digital Input/Output
AI:
Analogue Input
AO:
Analogue Output
AI/O:
Analogue Input/output
Basic Definitions
Password is set to 0123 and is used to access basic
parameter settings (see Table 3: Parameter settings). The
set-up programming is normally done in the factory during
manufacturing of the telephone sets. The factory settings
can be loaded into the EEPROM (see Figure 3: Memory
allocation for external EEPROM).
PIN code is default set to 1111 and is used by the user to
protect certain user settings (see Table 5: User
programming with PIN code). The PIN code can be
changed by the user.
Default settings are shown in bold.
Program procedures are entered with the [PG] key.
Pressing any invalid key or going on-hook during
programming will abort the program mode and no changes
will be stored. Ending a program procedure by pressing the
[PG] key will store the changes and exit the program mode.
Keyboard Layout
C4
C3
C2
C1
4
2
0
7
5
3
8
6
9
MR
R/P
FL
M5
1
M6
PG
V+
M7
V-
M8
#
M1
M2
M3
M4
SH
R1
R2
R3
MT
Figure 1: Keyboard Layout
Maximum R
ON
for key closure: 1 k
Minimum R
OFF
for open key: 1 M
See "Table 1: Key definitions" for description of key
functions
Datasheet AS2525
austria
micro
systems
Revision 2.1
Page 5 of 27
Key Definitions and Procedures
Table 1: Key definitions
Key
Condition
Function
Remark
[0] - [9],
[#], [
]
Off-hook
Digits
Function depending on mode
[
]
LD mode
Temporary MF select
Providing mixed mode dialing (default LD selected)
Speech mode
Enter program state
To enter the program state
[PG]
Program mode
Exit program state
To terminate/exit program state
Speech mode
Enter mute state
To enter mute state
Mute state
Exit mute state
To terminate/exit mute state
[MT]
Program mode
Enter blank
To enter blank digit during programming
Redial/Pause
Allows re-signaling of the last dialed number and
insertion of pauses
[R/P]
Program state
Pause
Each key pressure inserts a pause
[FL]
Flash function
Invokes a timed loop break
[V+]
Speech mode
Volume control
To increase the receive gain
[V-]
Speech mode
Volume control
To increase or decrease the receive gain
[MR]
Memory redial key
To access memory by key codes
[M1] - [M8]
Memory dial
Access keys to memories 1 to 8 and 9 to 16
[SH]
Second function (shift)
To access second function of keys
Table 2: Digits
Digit Key
DTMF Mode
(f
LOW
+ f
HIGH
)
Pulse Mode
Programming Mode
([PG] + Digit)
Memory Location
([MR] + Digit)
[0]
941 + 1336 Hz
10 pulses
Memory 17
[1]
697 + 1209 Hz
1 pulse
To enter PIN protected programming
Memory 18
[2]
697 + 1336 Hz
2 pulses
Select flash duration
Memory 19
[3]
697 + 1477 Hz
3 pulses
Select dialing mode
Memory 20
[4]
770 + 1209 Hz
4 pulses
Select pause duration
Memory 21
[5]
770 + 1336 Hz
5 pulses
Key lock toggle
Memory 22
[6]
770 + 1477 Hz
6 pulses
Ringer volume
Memory 23
[7]
852 + 1209 Hz
7 pulses
Ringer melody
Memory 24
[8]
852 + 1336 Hz
8 pulses
LCD contrast
Memory 25
[9]
852 + 1477 Hz
9 pulses
Ringer on/off
Memory 26
[
]
941 + 1209 Hz
Temporary MF select
-
[#]
941 + 1477 Hz
-
-
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