AN1500A PDS038-SA2532K-001 Rev. C 21-03-00
This application note describes the use of the SA2532K Single Chip Telephone IC developed specifically to meet
with India’s Department of Telecommunication (DOT) Specification for the Electronic Telephone Instruments. This
application note is based on the use of the multi-purpose demo board DB1500I with the SA2532K IC
•
High performance telephone with speech circuit, DTMF/Pulse dialer and tone ringer
•
Very few external low cost components
•
CMOS technology, far less sensitive to EMC
•
EMC proof single sided layout, provision for EMC blocking capacitors installed
•
Internally set real AC impedance to reduce external components
•
Sidetone programmable by two resistors and one capacitor
•
Ring frequency discrimination
•
Line loss compensation selectable by jumper
•
2 different flash timings selectable by 2 flash keys
•
31 digit last number redial
•
Sliding cursor protocol and pause key
•
One-touch repeat dialing
•
1 direct memory
•
Tone / Pulse switch
•
Modular connectors for handset and line cord, line connector a/b- terminals selectable by jumper
•
Layout prepared for 16kHz blocking filters
•
19-key SPST Keyboard on board
•
Tone LED output Indicator
•
Several hook transistor configurations
•
Over-voltage and over-current circuit options
sames
samessames
sames
AN1500A
APPLICATION NOTE
SINGLE CHIP TELEPHONE DEMO BOARD
SA2532K
1 Scope
2 Key Features
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TABLE OF CONTENTS
1 SCOPE................................................................................................................................................................. 1
2 KEY FEATURES ................................................................................................................................................. 1
3 OTHER APPLICABLE DOCUMENTS AND PAPERS........................................................................................ 4
4 REVISION STATUS............................................................................................................................................. 4
5 SA2532K PIN LAYOUT ...................................................................................................................................... 4
6 GENERAL DESCRIPTION.................................................................................................................................. 5
7 DEMO BOARD CONFIGURATION..................................................................................................................... 5
7.1 S
ETTING A/B LINE CONNECTION
........................................................................................................................ 6
7.2 C
ONNECTING A HANDSET
................................................................................................................................6
7.3 S
ETTING DIALING MODE
................................................................................................................................... 6
7.4 S
ETTING LINE LOSS COMPENSATION
(AGC)...................................................................................................... 6
7.5 AC
IMPEDANCE
............................................................................................................................................... 6
8 DESCRIPTION OF KEYBOARD FUNCTIONS................................................................................................... 7
8.1 N
UMERIC KEYS
............................................................................................................................................... 7
8.2 F
LASH KEYS
(R,R2)........................................................................................................................................ 7
8.3 L
AST NUMBER REDIAL K EY
(LNR) .................................................................................................................... 7
8.4 P
AUSE KEY
(PAUSE)...................................................................................................................................... 7
8.5 T
ONE
/ P
ULSE SWI T CHING
............................................................................................................................... 7
8.6 E
NTER
/M5...................................................................................................................................................... 7
9 USING THE SA2532K......................................................................................................................................... 8
10 SLIDING CURSOR PROTOCOL AND PAUSE INSERTION.......................................................................... 9
11 AC IMPEDANCE OF THE SA2532K............................................................................................................... 9
11.1 D
EMO BOARD MEASUREMENTS
:....................................................................................................................... 9
11.1.1 Definition:............................................................................................................................................... 9
11.1.2 Measurement:...................................................................................................................................... 10
12 SIDETONE CANCELLATION........................................................................................................................ 10
12.1 D
UAL SOFT CLIPPING
: ................................................................................................................................... 11
12.2 S
IDE TONE BALANCE NE T WORK
:..................................................................................................................... 11
12.3 E
XAMPLE
:..................................................................................................................................................... 11
13 THE DOUBLE WHEATSTONE PRINCIPLE ................................................................................................. 11
13.1 S
IDETONE CANCELLATION
.............................................................................................................................. 12
13.2 AC
IMPEDANCE
............................................................................................................................................. 12
14 FURTHER ADJUSTMENTS .......................................................................................................................... 13
14.1 F
REQUENCY RESPONSE SHAPING
: T
RANSMIT
................................................................................................. 13
14.1.1 Microphone gain setting....................................................................................................................... 13
14.1.2 Tx frequency shaping: ......................................................................................................................... 13
14.2 F
REQUENCY RESPONSE SHAPING
: R
ECEIVE
................................................................................................... 14
14.2.1 Receive gain setting: ........................................................................................................................... 14
14.2.2 Rx frequency shaping.......................................................................................................................... 14
14.2.3 Metering pulses filtering....................................................................................................................... 14
15 OFF-HOOK CONDITIONS & DC MASK...................................................................................................... 15
15.1 L
INE CURRENT PATH
...................................................................................................................................... 15
15.2 DC
MASK PATH
............................................................................................................................................. 15
15.2.1 Setting for low DC mask:..................................................................................................................... 15
15.3 S
PEECH MODE
.............................................................................................................................................. 16
15.4 DTMF
DIALING
............................................................................................................................................. 16
15.5 P
ULSE DIALING
.............................................................................................................................................. 16
15.6 P
RE-DIGIT
, I
NTER-DIGIT ,INTER-TONE AND ACCESS PAUSES
............................................................................ 17
16 HOOK TRANSISTOR OPTIONS................................................................................................................... 17
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16.1
ELECTRICAL REQUIREMENTS
.......................................................................................................................... 17
16.2 S
INGLE BIPOLAR TRANSISTOR
........................................................................................................................ 17
16.3 B
IPOLAR DARLINGTON TRANSISTOR
............................................................................................................... 18
16.4 VMOS-FET
WITH SURGE PROTECTION
.......................................................................................................... 18
16.5 VMOS-FET
WITH OVERCURRENT PROTECTION
.............................................................................................. 18
16.6 C
URRENT LIMITING
........................................................................................................................................ 19
16.7 O
VERVOLTAGE PROTECTION OF THE
PCB:..................................................................................................... 19
16.8 DC-
MASK FOR VARIOUS HOOK TRANSISTOR ARRANGEMENTS
.......................................................................... 20
17 SHUNT- AND RINGER TRANSISTORS ..................................................................................................... 20
18 ON-HOOK CONDITIONS .............................................................................................................................. 20
18.1 Q
UIESCENT CURRENT PA TH
........................................................................................................................... 21
19 RINGING MODE ............................................................................................................................................ 21
19.1 R
INGING FREQUENCY COMPARATOR
.............................................................................................................. 21
20 OSCILLATOR INPUT .................................................................................................................................... 21
21 EMC & RFI ISSUES....................................................................................................................................... 21
21.1 T
ECHNOLOGY
:.............................................................................................................................................. 21
21.2 L
AYOUT HINTS
: ............................................................................................................................................. 21
21.3 EMC
BLOCKING PARTS
: ................................................................................................................................ 22
21.4 B
LOCKING OF
AGND: ................................................................................................................................... 22
22 BOARD SCHEMATIC.................................................................................................................................... 23
23 BOARD LAYOUT........................................................................................................................................... 24
24 PART LIST..................................................................................................................................................... 25
25 APPLICATIONS............................................................................................................................................. 26
26 LIABILITY AND COPYRIGHT STATEMENT................................................................................................ 27
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1. Data Sheet SA2532KA/B
2. Pin-out Comparison SA2531 - SA2532
3. Application Note for Speaker Phone: Application Note SAN2202
4. Application Note for uC interface : Application Note SAN3010
5. Application Note for the Extraction of Power : Application Note SAN3020
6. Application note for using Dynamic Mic : Application Note SAN3021
AN1500 Application Note (this document):
AN1500 Demo Board Schematic Rev.: B
DB1500I Demo Board Layout Rev.: 1.0
1
2
3
4
5
6
7
8
9
10
11
12
13
14 15
16
17
18
19
20
21
22
23
24
25
26
27
28LS
RO1
RO2
VDD
A
GND
STB
CI
MO
LLC
HS/DPN
OSC
MODE OUT
C4
C3
RI
LI
VSS
CS
M2
M1
MODE
FCI
R1
R2
R3
R4
C1
C2
SA2532K
3 Other applicable documents and papers
4 Revision status
5 SA2532K Pin Layout .
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The SA2532K device was developed to provide “plug & play” solution for the Indian DOT, emphasizing high
performance voice transm ission and reception. In spite of the fact that voice transmission and reception are the
most vital features in telephony, they are very often ignored or given lower priority compared with som e more or
less useless non-voice features. No comprom ises were accepted during the des ign phase of the SA2532K, which
is based on the SA2531/2 speech circuit and which supersedes even the hardest PTT requirements worldwide.
The dialler part is based on a long history of producing a wide range of dialer circuits with user-fr iendly features in
compliance with various national PTT regulations. This knowledge enabled us to develop a specific product to meet
with DOT type approval.
The last piece in the puzzle to complete the full picture of the first CMOS single chip POT was the tone ringer. A
ring frequency discrimination circuit was implemented to avoid false “bell-tinkle” during pulse dialing from a parallel
telephone. The 3-tone melody generator provides the ringing signal.
Note: all the subsequent component numbering is ref e r enced t o the AN1500 schematic, shown in pt.22
The SA2532K is the rare combination of advanced technology and down-to-earth simplicity providing easy and
uncomplicated design effort for the telephone manufacturer. No fussing ar ound: Simply go by the straight forward
guidelines supplied by a highly experienced application group. No technology stress but appealing functionality.
See Fig. 1 for configuration locations:
Fig. 1: Demo board configuration
6 General Description
7 Demo board configuration
J2: Dial Mode
Selection
Line connector
Handset Connector
J3: line loss compensation
selector
Sidetone Network
Ringer Capsule
Connector
J1 :Line terminal selection
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7.1 Setting a/b line connection
J1 allows selection of a/b line term inals to
easily adapt the demo board to various
PTT line connections:
7.2 Connecting a handset
A handset connected at Z2 should have the following
connections:
remark: observe polarity of the electret microphone
7.3 Setting dialing mode
By J2, a selection of 3 different dialing modes can be
made, 2 pulse (=LD) dialing modes and a DTMF
dialing mode.
If LD Mode is selected then it is possible to switch
into MF mode by pressing the ! key but the mode
will return to LD after a hookswitch operation or after
a Recall (flash). In LD m ode pulsing is at 10 pulses
per second.
7.4 Setting line loss compensation (AGC)
Line loss compensation = line current dependent
gain setting of Tx and Rx amplifiers can be set by
jumper setting to 3 different modes : high, low and
no LLC (=default).
7.5 AC impedance
The Characteristic or output impedance of the SA2532K is set internally to 600Ω. No further components are
required. For a complex impedance refer to pt 11.
inner two pins (default) outer two pins (optional)
LD Mode
make/break
ratio 1:2
LD Mode
make/break
ratio 2:3
MF Mode
LLC 45 to 75mA LLC 20 to 50mA no LLC
Handset
J2
J2J2
J3
J3
J3
J1
J1
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The user-friendly operating procedures comply with different PSTN and PABX systems worldwide. By choosing
between the total of 19 keys it is possible to fit the SA2532K into most telephone designs.
The keyboard is connected to 8 pins of the SA2532K (C1...C4, R1...R4) by a n*m SPST keyboard matrix. To
extend two of the rows, a diode (D9 and D10) are added. This arrangement allows detection of 19 keys on a 4*4
matrix.
8.1 Numeric keys
The numeric k eys (1..0,!,#) are standard number dial k eys for both DT MF and pulse dialing (!and # only DTMF).
Additionally the !key can be used for temporary MF switching.
8.2 Flash keys (R,R2)
Selection of flash timing can be made by selecting one of the 2 flash keys :R1= 100ms and R2= 270ms.
8.3 Last number redial key (LNR)
The last number redial facility allows redialing of the last manually entered number by one keystroke. LNR is
repeatable after each off-hook. The LNR key also supports the sliding cursor protocol (see pt. 10) to allow
convenient redialing with PABX systems.
8.4 Pause key (PAUSE)
This key is to insert a pause in a digit string. Each pause is 2 seconds if inserted within the first 5 digits otherwise a
wait function will halt dialling until a PS or LNR key is depressed.
8.5 Tone / Pulse switching
When any of the LD dialing modes is selected (see pt. 7.3), a switch to temporary MF can be performed by
pressing the ! key to get into DTMF mode and one of the flas h (R)-keys to get back to pulse dialing. Once in MF
mode the mode output LED is active.
Remark: tem porary MF can only be activated, when the initial dialing mode s elected by J2 (see pt. 7.3) is in one of
the pulse dialing modes.
8.6 Enter/M5
The ENTER key is used to program the m emory (M5). Pressing ENTER followed by the key M5 opens the mem ory
location for storing the number.
8 Description of keyboard functions
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The DB1500I demo board is delivered with an SA2532K installed and the key functions are according to the c hip
are illustrated below.
Fig. 2: SA2532K keyboard labels
9 Using the SA2532K
MUTE
12
M5
8
7654
3
0
R2
R
#
*9
PAUSE
LNR
ENTER
C1 C2 C3 C4
R1
R2
R3
R4
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To accommodate easy and uncomplicated redialing behind a PABX, a
sliding cursor
protocol is implemented:
if a manually entered digit string matches the contents of the LNR memory, pressing LNR will only dial out the
remaining digits :
example: desired number 0123456 (where 01 is the access code)
off-hook, manual entry =
01
-wait for dial tone -
23456
- line is busy -on-hook
(LNR contents is 0123456)
off-hook, manual entry =
01
-wait for dial tone - press
LNR
key:
LNR dials out the remaining digits: 23456
The SA2532K is designed for applications requiring a characteristic impedance of 600 Ohms, no connection should
be made to CI (pin 7) if a real impedance is required. Should a complex impedance be required a capacitor of
approximately 1/10 of the complex part of the impedance should be connected to CI. Every complex impedance
consists of a real and complex part. The ac impedance of the SA2532K is calculated by
Z
AC
= Z
SYN
+ Z1
Where :
Z1 = the external resistor connected between pin 1(LS) and pin 27 (LI) . This resistor is also used by the device for
current monitoring and sets the DC resistance. To maintain correct operation the value of this resistor should be
set to 30 Ohm.
Z
SYN
= the internally synthezised impedance.
For real impedances
Z
SYN
= 19 * Z1
Z
AC
= (19*Z
SYN
) + Z1
Z
AC
= 20 * Z1 = 600 Ohm
If a impedance lower than Z
AC
is required, then a external parallel impedance should be added between LS and
V
SS
. To calculate the resulting AC impedance, any parallel impedance path between LS and VSS should be
considered. For example, if a bipolar line transistor is used, the resistance from the transistors base to VSS (Z
P
) is
in the order of 10K (R10). If a MOSFET is used then Z
P
is in the order of 100K which is negligible.
Z
AC
= 600//Z
P
Care must be taken when selecting the value of ZP since the value chosen should be such that the line transistor is
driven into full saturation.
11.1 Demo board measurements:
11.1.1 Definition:
return loss is defined as:
returnloss
Zref Zx
Zref Zx
=
+
−
20*log
where: Zref = the reference AC impedance (= the line termination)
Zx = the AC impedance of the telephone under test
10 Sliding cursor protocol and pause insertion
11 AC impedance of the SA2532K
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