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
sames
sames
sames
AN1500A
APPLICATION NOTE
SINGLE CHIP TELEPHONE DEMO BOARD
SA2532K
1 Scope
2 Key Features
AN1500A
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2/27
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 KEY
(LNR) .................................................................................................................... 7
8.4
P
AUSE KEY
(PAUSE)...................................................................................................................................... 7
8.5
T
ONE
/ P
ULSE SWITCHING
............................................................................................................................... 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
S
OFT CLIPPING
: ................................................................................................................................... 11
12.2 S
IDE TONE BALANCE NETWORK
:..................................................................................................................... 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
AN1500A
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3/27
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
L
IMITING
........................................................................................................................................ 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 PATH
........................................................................................................................... 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
AN1500A
sames
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5/27
The SA2532K device was developed to provide "plug & play" solution for the Indian DOT, emphasizing high
performance voice transmission 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 some more or
less useless non-voice features. No compromises were accepted during the design 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-friendly 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 referenced to 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 around: 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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