austriamicrosystems
Single-Chip Handsfree Phone
CMOS Integrated Circuit
AS2525
Key Features
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DATA SHEET
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.
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.
Block Diagram
LS
V
DD
V
DD
LINE
SENSE
SUPPLY
V
REF
FT2
A
GND
A
GND
NOISE
DET.
+
CS
–
SS
V
PP
V
SS
CI
300
Ω
RI
STB
–
+
PEAK
DET.
+
+
A
GND
PEAK
DET.
M4
V
PP
V
SS
–
+
VOICE
SWITCHING
V
PP
LO1
–
M3
V
DD
M2
CBN
FT1
M1
V
DD
30
Ω
LI
AS2525
LO2
V
SSA
RECI
Z
BAL
HS
HF
DM/HM
DEBOUNCE
DTMF
MELODY
RECV
RO
FCI
DPN
LED
CPU
DIALLER
DC/DC
CONVERTER
KEYSCANNING
OSCILLATOR
DI DO CLK
CS1 CS2
KEYBOARD (C1-4/R1-3)
3.58
MHz
CM
Revision 2.1
Page 1 of 27
Datasheet AS2525
austriamicrosystems
Pin Description
Pin #
1
Symbol
CS2
Type
DO
Description
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 kΩ) 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
4
HF
HS
DI
DI
H
ands
F
ree Switch Input
This is a Schmitt-trigger input that is pulled high to enable handsfree operation.
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
6
7
8
9
10
11
12
FT1
FT2
M4
M2
M3
M1
STB
CS
AI
AI
AI
AI
AI
AI
AI
AO
Analogue input pin for connecting a capacitor for offset cancellation.
Analogue input pin for connecting a capacitor for offset cancellation.
M
icrophone Input
4
Differential input for the handsfree microphone (electret).
M
icrophone Input
2
Differential input for the handset microphone (electret).
M
icrophone Input
3
Differential input for the handsfree microphone (electret).
M
icrophone Input
1
Differential input for the handset microphone (electret).
S
ide
T
one
B
alance Input
Analogue input for side tone cancellation network.
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
14
15
16
V
SS
LI
RI
SS
Supply
AI
AI
AO
V
oltage
S
ource
S
ource
Negative Power Supply.
L
ine
I
nput
Analogue input used for power extraction and line current sensing.
R
eceive
I
nput
Analogue input for ac-separated receive signal.
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
18
LS
CI
AI
AI
L
ine Current
S
ense Input
Analogue input for sensing the line current.
C
omplex
I
mpedance Input
Analogue input pin for the capacitor to program a complex impedance.
Revision 2.1
Page 2 of 27
Datasheet AS2525
austriamicrosystems
Pin #
19
Symbol
RECI
Type
AI
Description
REC
eive
I
nput
Analogue input for the handsfree receive path. Should be connected to RO via a coupling
capacitor.
20
21
22
23
24
25
RECV
RO
V
DD
A
GND
CBN
CM
AI
AO
Supply
Supply
AI
DO
REC
eive
V
oice Switching Input
Analogue input for receive voice switching path.
R
eceive
O
utput to
H
andset
Output for driving a dynamic earpiece with an impedance from 150
Ω
to 300
Ω
.
V
oltage
D
rain
D
rain
Positive Power Supply.
A
nalogue
G
rou
nd
Special ground for the internal amplifiers.
Analogue input pin for connecting a capacitor for background noise monitoring.
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.
Loudspeaker Power Supply
High power supply for the output driver stage.
26
27
28
29
30
V
PP
LO1
LO2
V
SSA
DM/HM
Supply
AO
L
oudspeaker
O
utputs
1/2
Output pins for a 32
Ω
( 25 to 50
Ω
) loudspeaker.
Power supply pin for LO1-LO2 output amplifier.
Supply
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
32
33
34
35
36
37
38
39
40
41
FCI
LED
OSC
R1
R2
R3
C1
C2
C3
C4
CLK
DI
DO
F
requency
C
omparator
I
nput
This is a Schmitt-trigger input for ring frequency discrimination. Disabled during off-hook.
LED
Output
Digital output for connecting 2 mA LED to indicate handsfree mode.
Osc
illator Input
Input for ceramic resonator 3.58 MHz.
DI/O
Keyboard
R
ows
C
olumns
(see Figure 1: Keyboard Layout).
DI/O
Keyboard
(see Figure 1: Keyboard Layout).
DO
Cl
oc
k
Clock output for 3-wire bus.
If signal is not activated, a pull down resistor (100 k
Ω
) 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
Ω
) is inserted.
Revision 2.1
Page 3 of 27
Datasheet AS2525
austriamicrosystems
Pin #
43
Symbol
DO
Type
DO
Description
D
ata
O
utput
Data output of 3-wire bus.
A 100 k
Ω
resistor connected from this pin to VSS enables key locking.
If signal is not activated, a pull down resistor (100 k
Ω
) 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
Ω
) is inserted.
DI:
DO:
DI/O:
Digital Input
Digital Output
Digital Input/Output
AI:
AO:
AI/O:
Analogue Input
Analogue Output
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
C1
C2
C3
C4
1
2
3
MR
V+
M1
M5
4
5
6
PG
V-
M2
M6
7
8
9
R/P
MT
M3
M7
∗
0
#
FL
SH
M4
M8
R1
R2
R3
Figure 1: Keyboard Layout
Maximum R
ON
for key closure: 1 k
Ω
Minimum R
OFF
for open key: 1 M
Ω
See “Table 1: Key definitions” for description of key
functions
Revision 2.1
Page 4 of 27
Datasheet AS2525
austriamicrosystems
Key Definitions and Procedures
Table 1: Key definitions
Key
[0] - [9],
[#], [∗]
[∗]
[PG]
Condition
Off-hook
LD mode
Speech mode
Program mode
Speech mode
[MT]
Mute state
Program mode
[R/P]
Program state
[FL]
[V+]
[V-]
[MR]
[M1] - [M8]
[SH]
Speech mode
Speech mode
Pause
Flash function
Volume control
Volume control
Memory redial key
Memory dial
Second function (shift)
Digits
Temporary MF select
Enter program state
Exit program state
Enter mute state
Exit mute state
Enter blank
Redial/Pause
Function
Remark
Function depending on mode
Providing mixed mode dialing (default LD selected)
To enter the program state
To terminate/exit program state
To enter mute state
To terminate/exit mute state
To enter blank digit during programming
Allows re-signaling of the last dialed number and
insertion of pauses
Each key pressure inserts a pause
Invokes a timed loop break
To increase the receive gain
To increase or decrease the receive gain
To access memory by key codes
Access keys to memories 1 to 8 and 9 to 16
To access second function of keys
Table 2: Digits
Digit Key
[0]
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[∗]
[#]
DTMF Mode
(f
LOW
+ f
HIGH
)
941 + 1336 Hz
697 + 1209 Hz
697 + 1336 Hz
697 + 1477 Hz
770 + 1209 Hz
770 + 1336 Hz
770 + 1477 Hz
852 + 1209 Hz
852 + 1336 Hz
852 + 1477 Hz
941 + 1209 Hz
941 + 1477 Hz
Pulse Mode
10 pulses
1 pulse
2 pulses
3 pulses
4 pulses
5 pulses
6 pulses
7 pulses
8 pulses
9 pulses
Temporary MF select
-
To enter PIN protected programming
Select flash duration
Select dialing mode
Select pause duration
Key lock toggle
Ringer volume
Ringer melody
LCD contrast
Ringer on/off
Programming Mode
([PG] + Digit)
Memory Location
([MR] + Digit)
Memory 17
Memory 18
Memory 19
Memory 20
Memory 21
Memory 22
Memory 23
Memory 24
Memory 25
Memory 26
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Revision 2.1
Page 5 of 27
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