Features
Speech Circuit
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Adjustable DC Characteristic
Symmetrical Input of Microphone Amplifier
Receiving Amplifier for Dynamic or Piezo-electric Earpieces
Automatic Line-loss Compensation
Dialer
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DTMF/Pulse Switchable
Pulse Dialing 66/33 or 60/40 or DTMF Dialing Selectable by Pin
Selectable Flashing Duration by Key Pad
Pause Function
Optical Indication of Temporary DTMF Mode
Keytone for Pulse Dialing
Last Number Redial up to 32 Digits
Three by 17 Digits Direct (One-touch) Memory
Ten by 17 Digits Indirect (Two-touch) Memory
Notice Function up to 32 Digits
Standard Low-cost Crystal 3.58 MHz or Ceramic Resonator
Handset Mute (Privacy) with Optical Indication
Additional Toggle Flipflop
Internal Loop Interrupt Detection
Universal
Telephone IC -
All Functions
Integrated
U3761MB-T
Tone Ringer
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2-tone Ringer
Adjustable Volume
RC Oscillator
Adjustable Threshold
Benefits
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Low Number of External Components
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High Quality through One IC Solution
Electrostatic sensitive device.
Observe precautions for handling.
Description
Atmel’s low-voltage telephone circuit U3761MB-T performs all the speech and line
interface functions required in an electronic telephone set, a tone ringer, a pulse and
DTMF dialing with redial, notice function, and 13 memories. Operation below 15 mA is
possible with reduced performance.
Rev. 4744A–CORD–09/03
Figure 1.
Block Diagram
2
Tip
VI
100 kW
HKS 1a
470
W
3 kW
33 kW
18 kW
220 nF
2N5401
CL
2.2 nF
XT
MIC2
2.2 µF
HKS
MODE
PRIND
Mask
DP
VDD
MFO
MIC1
MICO
TIN
13 V/
1W
Ring
220 nF
75 V
HKS 1b
5 MW
220 kW
1 µF
1 kW
220 µF
LED
4.7 V
Next to VDD
and GND
MPSA42
470 nF
4.7 V
Important note:
Application examples have not been examined for
series use or reliability, and no worst case scenarios
have been developed. Customers who adapt any of
these proposals must carry out their own testing and
be convinced that no negative consequences arise
from the proposals.
U3761MB-T
to key
board
matrix
Transmit
amplifier
CLIM
VL
330
W
2.4 kW
680
W
3.58 MHz
XT
Clock
generator
+
Micro-
phone
-
amplifier
Control
function
Sidetone
amplifier
ST
Earth
KT
Mute
control
3.3 nF
C1
C2
Pulse
control
logic
47 nF
RECIN
2.2 µF
C3
Receiver
attenuation
C4
Read - write
counter
Control
logic
Supply
current
regulator
R1
1
2
3
S M1
R2
Control
function
Receiving
amplifier
RECO1
1.8 kW
100
W
RECO2
12 kW
AGC
RDC
VI
300
W
39
W
1W
100 µF
4
5
6
M2
R3
Key-
board
inter-
face
RAM
7
8
9
A M3
R4
*/T 0
# R/P N
F1 F2 F3 E
Location
latch
Data
latch &
decoder
D/A
converter
ROW & column
programmable
counter
AGC
current
generator
VI
MFIND
MUTE
VRING
10 µF
TEST
Supply
Power on reset
10 kW
OUT
1 nF
RCK
Clock signal
oscillator
Divider
Tone signal
generator
VRIAC
10 kW
150 kW
HFI
HFO
Toggle
flipflop
Divider
Bandgap
reference
Comparator
with hysteresis
THA
4744A–CORD–09/03
Pin Description
Pin
1
2
3
Symbol Function
C1
C2
C3
C1
VDD
VDD
Configuration
Keyboard input
VDD
PD
4
C4
C2-C4
VDD
PD = Protection Device
VDD
5
Earth
Earth key (604 ms high pulse, 1 s pause)
EARTH
PD
VDD
6
HFI
VDD
PD
VDD
7
HFO
Output will be toggled by each LOW/HIGH edge at HFI
HFO
PD
4
U3761MB-T
4744A–CORD–09/03
200K
Toggle flipflop input
Input with 200 kW pull-down resistor
HFI triggers HFO with each LOW/HIGH edge
HFI
U3761MB-T
Pin Description
Pin
Symbol Function
Configuration
VDD
XT
VDD
8
9
XT
XT
A built-in inverter provides oscillation with an inexpensive
3.579545-MHz crystal or ceramic resonator
VDD
PD
XT
VDD
PD
10
MFO
Output of DTMF
DTMF output frequency
Specified (Hz) Actual (Hz) Error (%)
R
1
697
699
+0.28
766
-0.52
R
2
770
R
3
852
848
-0.47
940
-0.10
R
4
941
1216
+0.57
C
1
1209
C
2
1336
1332
-0.30
1472
-0.34
C
3
1477
VDD
MFO
VDD
PD
VDD
11
MFIND
During the temporary DTMF mode the output switches to
low
Reset by on hook condition
Maximum voltage at MFIND = 5.5 V
MFIND
MFIND
PD
12
GND
Ground
VI
1V
50K
PD
13
14
MIC 1
MIC 2
Inverting input of microphone amplifier
Non-inverting input of microphone amplifier
MIC1
MIC2
50K
1V
VI
PD
5
4744A–CORD–09/03
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