OKI MSM7715

E2A0030-16-X1
¡ Semiconductor
MSM7715
¡ Semiconductor
This version: Jan.
1998
MSM7715
Previous version: Nov. 1996
Multi-Function Telecommunication LSI
GENERAL DESCRIPTION
The MSM7715 is a signal transmitting and receiving LSI device for applications such as
telemeters. The MSM7715 uses a no-ringing communication mode. Built-in functions includes
a 300 bps full-duplex modem complying with ITU-T V.21, a DTMF signal (PB signal) generator
and receiver, and a call progress tone (CPT) detector. The answer tone (1650 Hz) generation can
be accomplished with the built-in modem.
A meter terminal can be configured using this transmitting and receiving device along with the
meter, NCU, and controller.
FEATURES
• 3 V power supply. (Voltage range is 2.5 V to 3.6 V.)
• Selectable modes, including DTMF signal sending mode, DTMF signal receiving mode, and
V.21 modem answer/originate mode.
• For DTMF signal reception, support for normal detection mode or high-speed detection mode.
• For call progress tone detection, support for rectangular wave output or detection output.
• DTMF signal receiving output, which is in a 3-state mode, is able to be connected externally
with the DTMF signal sending 4-bit input.
• Analog loopback test and remote digital loopback test supported.
• Dedicated pins for modem sending/receiving data, carrier detection, sending request, and call
progress tone detection.
• Independent external adjustment of the analog signal using the modem signal and DTMF
signal.
• External adjustment of the carrier detection level.
• Internal 3.579545 MHz crystal oscillation circuit.
• Power-down mode
• Package:
44-pin plastic QFP (QFP44-P-910-0.80-2K)
(Product name : MSM7715GS-2K)
1/21
PreLPF
+
–
AIN
2765 Hz
BEF
DT2
DTMF
Receiver
DT3
DT4
4 dB
SP
Smooth
AOUT
CPT
Detector
–
+
*
CP
*
Carrier
Detector
GAT2
RD
FSK Modem
MOD
*
TD
*
RS
Voltage
Ref.
VR1
CPW
CD
–
+
GAT1
DTTIM
¡ Semiconductor
BLOCK DIAGRAM
DT1
CLK
X2
VR2
X1
SGO
SG
SGC
DTMF
Generator
DTO
PON
VDD
Power ON
+3 V
0V
2/21
*
MODE1
*
MODE2
*
MODE3
*
ICTA
*
ICTB
*
TEN
*
DTG1
*
DTG2
*
DTG3
*
DTG4
Note)
DT1 to DT4 :
3-state outputs
* : Input with
pull-up resistor
MSM7715
GND
*
Mode
Select
&
Test
¡ Semiconductor
MSM7715
DTG3
DTG2
DTG1
GND
VR2
VR1
DTO
MOD
GAT2
GAT1
SGC
44
43
42
41
40
39
38
37
36
35
34
PIN CONFIGURATION (TOP VIEW)
28
NC
ICTB
7
27
AOUT
DTTIM
8
26
NC
MODE1
9
25
NC
MODE2
10
24
PON
MODE3
11
23
SP
22
6
DT4
ICTA
21
VDD
DT3
29
20
5
DT2
CPW
19
NC
DT1
30
18
4
CP
RS
17
AIN
CD
31
16
3
RD
TD
15
SGO
CLK
32
14
2
NC
TEN
13
NC
X2
33
12
1
X1
DTG4
44-Pin Plastic QFP
NC : No connect pin
3/21
¡ Semiconductor
MSM7715
PIN DESCRIPTION
Name
Description
Pin No.
I/O
DTG4
1
I*
Input for specifying the DTMF code to be sent.
TEN
2
I*
Input for controlling output of the DTMF signal. (Transmit enable)
DTG1 to DTG4 are latched at the falling edge of TEN and the DTMF signal is
output when “0” is input. See Fig. 2.
TD
3
I*
Input for data to be sent to the modem. Input the data string at a speed of 300 bps
or lower.
RS
4
I*
Input for controlling the modem sending output. (Request to send)
The sending signal is output when “0” is input.
I*
Input for selecting the output waveform from the call progress tone detector.
When "1" is input, a rectangular wave that is synchronized with the input signal is
output from the CP.
When "0" is input, presence of detected signal is output from the CP pin. See Fig.3.
I*
Inputs for testing. Leave them open or connect them to VDD.
I*
Input pin for controlling the detection timing of the DTMF receiver.
When “0” is input, the high-speed detection mode is selected.
I*
Input for selecting the operation mode. See Table 1.
CPW
5
ICTA
6
ICTB
7
DTTIM
8
MODE1
9
MODE2
10
MODE3
11
X1
12
I
X2
13
O
Input and output connected to the crystal oscillator. See “Oscillation Circuit” in
the Functional Description.
CLK
15
O
3.579545 MHz clock output
RD
16
O
Output for serial data received by the modem. It is held in the marked state
(“1”) when the carrier detector (CD) does not make detection.
CD
17
O
Output for the carrier detector. “0” means detection, while “1” means
non-detection.
CP
18
O
Output for call progress tone (CPT) detection. When the CPT is detected,
the waveform selected by the CPW pin is output. See Fig. 3.
DT1
19
DT2
20
DT3
21
O
Outputs for the code of the received DTMF signal. In a mode other than the
DTMF receiving mode, these pins are in a high-impedance state.
DT4
22
SP
23
O
Output for presenting the DTMF signal receiving data. “1” means that the DTMF
signal is being received. Latch DT1 to DT4 at the rising edge of SP.
See Fig. 1.
PON
24
I*
Input for controlling power-on. When “1” is input, all lines of this device enter the
power down state, and then the operation of each funciton stops and the receiver
timer is reset.
AOUT
27
O
Analog signal output. The DTMF signal or modem sending signal is output.
4/21
¡ Semiconductor
Name
MSM7715
Pin No.
I/O
VDD
29
—
Power supply. Supply +2.5V to 3.6V.
AIN
31
I
Input for the analog receiving signal.
SGO
32
O
Output for the signal ground voltage. The output voltage is 1/2 VDD.
Connect a capacitor of 0.1 mF or more between SGO and GND.
SGC
34
—
Pin for connecting the capacitor of the signal ground voltage generating circuit.
Connect a capacitor of 1 mF or more between SGC and GND.
GAT1
35
I
Input for the sending output level-adjusting amplifier.
GAT2
36
O
Output for the sending output level-adjusting amplifier.
MOD
37
O
Output for the sending modem signal.
DTO
38
O
Output for the DTMF signal.
VR1
39
O
Output for the reference voltage generating circuit.
The potential difference between VR1 and SGO is approximately +0.75 V.
VR2
40
I
Input for external adjustment of the modem’s carrier detection level.
GND
41
—
Ground.
DTG1
42
DTG2
43
I*
Inputs for specifying the DTMF code to be sent.
Data is latched at the falling edge of TEN.
DTG3
44
Note:
Description
Digital inputs that are pulled up internally by a high resistance.
5/21
¡ Semiconductor
MSM7715
ABSOLUTE MAXIMUM RATINGS
Parameter
Power Supply Voltage
Input Voltage
Storage Temperature
Symbol
Condition
Rating
Unit
VDD
Ta = 25°C
With respect to GND
–0.3 to 7
V
VI
–0.3 to VDD + 0.3
V
TSTG
—
–65 to +150
°C
RECOMMENDED OPERATING CONDITIONS
Symbol
Condition
Min.
Typ.
Max.
Unit
Power Supply Voltage
Parameter
VDD
—
2.5
3.0
3.6
V
Operating Temperature Range
Top
—
°C
VIH
Input Voltage
—
VIL
Input Clock Frequency
X1/X2 Load Capacitance
–40
—
+85
0.8 VDD
—
VDD
0
—
0.2 VDD
fCLK
Against 3.579545 MHz
–0.1
—
+0.1
%
C1, C2
—
—
12
—
pF
SGC Bypass Capacitance
C3
—
—
1
—
SGO Bypass Capacitance
C6
—
0.1
—
—
VDD Bypass Capacitance
Crystal
V
mF
C5
—
10
—
—
Oscillation Frequency
—
—
—
3.579545
—
Frequency Deviation
—
At 25°C ±5°C
–100
—
+100
Temperature
Characteristics
—
At –40°C to +85°C
–50
—
+50
Equivalent Series
Resistance
—
—
—
—
90
W
Load Capacitance
—
—
—
16
—
pF
MHz
ppm
ELECTRICAL CHARACTERISTICS
DC Characteristics
(VDD = 2.5 V to 3.6 V, Ta = –40°C to +85°C)
Parameter
Symbol
IDD1
Power Supply Current
Input Current
*1
IDD2
Condition
PON = "0"
IDDS
PON = "1"
IIH
VIH = VDD
IIL
VIL = 0 V
VOH1
Output Voltage
Notes:
*2
VOL1
*2
Min.
Typ.
Max.
Modem mode
—
3
6
DTMF mode
—
2.4
5
Power-down
—
1
20
–10
—
10
–50
–10
10
IOH = –100 mA
VDD – 0.1
—
VDD
IOL = 100 mA
0
—
0.1
VOH2
CLK
IOH = –100 mA
0.9 VDD
—
VDD
VOL2
CL£10 pF
IOL = 100 mA
0
—
0.1 VDD
Unit
mA
mA
V
*1 The following pins have an internal pull-up resistor. : DTG1 to DTG4, TEN, TD, RS,
CPW, ICTA, ICTB, DTTIM, MODE1 to MODE3, and PON
*2 RD, CD, CP, DT1 to DT4, and SP
6/21
¡ Semiconductor
MSM7715
AC Characteristics (DTMF)
(VDD = 2.5 V to 3.6 V, Ta = –40°C to +85°C)
Parameter
Transmit Level
Transmit Signal Level
Relative Value
Transmit Frequency
Deviation
Transmit Signal
Distortion Rate
Symbol
VDTTL
VDTTH
VDTDF
fDDT
THDDT
Condition
Min.
Typ.
Max.
Unit
Low-group tone
–16.5
–14.5
–12.5
dBm
High-group tone
–15.5
–13.5
–11.5
*1
0
1
2
dB
–1.5
—
+1.5
%
Harmonics/Fundamental frequency
—
—
–23
dB
AOUT, R1 = R3
High-group tone/low-group tone
With respect to the nominal frequency
DTG1 to DTG4 Input Data
Setup Time
tSDT
See Fig. 2.
250
—
—
DTG1 to DTG4 Input Data
Hold Time
tHDT
See Fig. 2.
250
—
—
ns
Receive Detect Level
VDETDT
For each single tone
–46
—
–10
dBm
Receive Reject Level
VREJDT
For each single tone
—
—
–60
*1
Receive Frequency
Detect Band
fDETDT
With respect to the nominal frequency
—
—
±1.5
Receive Frequency
Reject Band
fREJDT
With respect to the nominal frequency
Allowable Receive Level
Difference
VTWIST
Allowable Receive
Noise Level ratio
Dial Tone Reject Ratio
Signal Repetition Time
Tone Time for Detect
Tone Time for No Detect
Output Delay Time
Interdigit Pause Time
Acceptable Drop Out Time
SP Delay Time
Output Trailing Edge
Delay Time
%
VN/S
VREJ400
±3.8
—
—
High-group tone/low-group tone
–6
—
+6
Noise (0.3 kHz to 3.4 kHz)
level/tone level
—
–12
—
380 Hz to 420 Hz
37
—
—
tC1
DTTIM = "1"
120
—
—
tC2
DTTIM = "0"
70
—
—
DTTIM = "1"
49
—
—
DTTIM = "0"
34
—
—
tI1
DTTIM = "1"
—
—
24
tI2
DTTIM = "0"
—
—
9
tS1
tS2
See Fig. 1
tG11
Normal
DTTIM = "1"
30
45
57
tG12
condition *2
DTTIM = "0"
20
32
42
tG21
Just after
DTTIM = "1"
30
48
77
tG22
mode change *3 DTTIM = "0"
20
35
62
tP1
DTTIM = "1"
30
—
—
tP2
DTTIM = "0"
21
—
—
tB1
DTTIM = "1"
—
—
10
tB2
DTTIM = "0"
—
—
3
tSP1
DTTIM = "1"
6
8
10
DTTIM = "0"
1
1.7
3
tD1
tS > 80 ms
DTTIM = "1"
21
29
35
tD2
tS > 44 ms
DTTIM = "0"
15
21
27
tSP2
dB
ms
7/21
¡ Semiconductor
Note:
MSM7715
*1 0 dBm = 0.775 Vrms (For all AC characteristics)
*2 "Normal condition" means that a DTMF signal appears after more than 20 ms after
setting DTMF receive mode.
*3 "Just after mode change" means that there is an input signal when the mode is
changed from DTMF transmit mode to DTMF receive mode. If there is an input
signal when power is turned on, see "DTMF mode setting procedure after power on
or after releasing power down mode".
AC Characteristics (Modem)
(VDD = 2.5 V to 3.6 V, Ta = –40°C to +85°C)
Parameter
Symbol
Min.
Typ.
Max.
Unit
Modem Transmit Level
VAOM
Measured at AOUT pin, R1 = R2
–11
–9
–7
dBm
Signal Level Relative Value
VDM
Mark signal/space signal
dB
fOM
Modem Transmit
Carrier Frequency
fOS
fAM
fAS
Transmit Signal Output Deray
Condition
Originate mode
Answer mode
–1.5
0
1.5
Mark, TD = "1"
976
980
984
Space, TD = "0"
1176
1180
1184
Mark, TD = "1"
1646
1650
1654
Space, TD = "0"
1846
1850
1854
—
3.5
—
–48 *1
—
–6
–42
tADD
TD Æ AOUT
Modem Receive Signal Level
VAIM
Measured at AIN. FSK modulation signal
Carrier Detection (CD)
Signal Level
VON
Answer mode : 1080 Hz
OFFÆON
—
–44
VOFF
Originate mode : 1750 Hz
ONÆOFF
–48
–46
—
CD Level Hysteresis
VHYS
VR2 open at AIN pin
—
2
—
tCDD1
OFF Æ –6 dBm
—
8
—
tCDD2
OFF Æ –40 dBm
5
14
22
tCDH1
–6 dBm Æ OFF
20
31
40
tCDH2
–40 dBm Æ OFF
—
23
—
Time
CD Delay Time
CD Hold Time
Hz
ms
dBm
dB
ms
Demodulated Data Bias
Distortion
DBS
300 bps,1 : 1 pattern
—
—
±10
%
NRTS Signal Versus
Modem Receive Signal
Allowable Level Ratio
VNR
VNRTS/V receive modem signal
NRTS : 2765 Hz ±30 Hz
—
—
–2
dB
Receive data output Delay
Time
tRDD
AIN Æ RD
—
5
—
ms
*1 When the carrier detector does not detect (CD="1"), RD is fixed to "1".
AC Characteristics (Call progress tone detector)
(VDD = 2.5 V to 3.6 V, Ta = –40°C to +85°C)
Min.
Typ.
Max.
Unit
CPT Detect Level
Parameter
Symbol
VDETCP
400 Hz
Condition
–40
—
–6
dBm
CPT Non-Detect Level
VREJCP
400 Hz
—
—
–60
dBm
CPT Detect Frequency
fDETCP
See Fig. 3.
380
—
420
Hz
500
—
—
—
—
300
CPT Non-Detect Frequency
fREJCP
CPT Detect Delay Time
tDELCP
—
—
20
—
ms
CPT Detect Hold Time
tHOLCP
—
—
15
—
ms
See Fig. 3.
Hz
8/21
¡ Semiconductor
MSM7715
AC Characteristics
(VDD = 2.5 V to 3.6 V, Ta = –40°C to +85°C)
Parameter
Symbol
Min.
Typ.
Max.
Unit
AOUT
—
—
1.1
Vp-p
MOD, DTO, GAT2
20
—
—
Resistor between VR1 and SGO
40
—
—
RLAO
AOUT
30
—
—
ROX
AOUT, MOD, DTO, GAT2, VR1, SGO
—
100
—
W
—
10
—
MW
Transmit Signal Output Level
VAOUT
Output Load Resistance
RLVR1
RLX
Output Impedance
Input Impedance
Output DC Potential
Condition
RAI
GAT1, AIN
VSG
SGO
VDCAO
AOUT
—
VDD/2
—
Potential difference between VR1 and SGO
0.7
0.75
0.8
4 kHz to 8 kHz
—
—
–45
Measured at AOUT
8 kHz to 12 kHz
—
—
–65
R1= 30 kW
every 4 kHz
C4 = 680 pF
bandwidth of
VREF
VS1
VS2
Out-of-band Output Noise
VS3
kW
VDD/2–0.1 VDD/2 VDD/2+0.1
V
dBm
—
–70
–60
12 kHz or more
9/21
¡ Semiconductor
MSM7715
TIMING DIAGRAM
When DTMF is received
tC
tI
tS
tP
tB
AIN signal
tG
DT1 to 4
SP
tD
tSP
Figure 1 DTMF Receive Timing
tS
tI
tP
tB
tSP
tC
tG1n
tD
: Tone time for detect
When the input signal duration is tS or more, receiving is normally done.
: Tone time for no detect
When the input signal duration is tI or less, this input signal is ignored and DT1 to
DT4 and SP is not output.
: Interdigit pause time
When there is no input signal for tP or more, DT1 to DT4 and SP are reset.
: Acceptable drop out time
DT1 to DT4 and SP are not reset even though a no-signal state for tB or less
(momentary no-signal) occurs during signal receiving. The tB is applicable while
the received signals are output. (SP="1")
: SP delay time
Against the DT1 to DT4 output, SP is output after a delay of tSP. Therefore, latch DT1
to DT4 at the rising edge of SP.
: Signal repetition time
For normal receiving, set the signal repetition time to tC or more.
: Output delay time (n: 1 or 2)
Against the appearance of the input signal, DT1 to DT4 are outputs after a delay of
tG1n.
: Output trailing edge delay time
Against the stop of the input signal, DT1 to DT4 and SP stop outputting after a delay
of tD.
10/21
¡ Semiconductor
MSM7715
When the DTMF tone is sent
TEN
tSDT
tHDT
DTG1
DTG2
DTG3
DTG4
DTO
941 Hz + 1447 Hz
Figure 2 DTMF Transmit Timing
When the call progress tone (CPT) is detected
400 Hz
AIN
CP
CPW = "1"
CP
CPW = "0"
tDELCP
tHOLCP
Figure 3 Call Progress Tone Detect Timing
11/21
¡ Semiconductor
MSM7715
FUNCTIONAL DESCRIPTION
Oscillation circuit
Connect a 3.579545 MHz crystal resonator between X1 and X2. If the load capacitance of the
crystal resonator is 16 pF, connect a 12 pF capacitor between X1 and GND and between X2 and
GND.
When an external clock is used, input the external clock to X2 via a 200 pF capacitor and leave
X1 open.
C1
X1
X1
C2
X2
X2
3.579545 MHz
3.579545 MHz
Figure 4 Connection of
the Crystal Resonator
Figure 5 Connection of
the External Clock
Signal ground
Connect a capacitor of 1 mF between SGC and GND. Do not connect anything other than this
capacitor to the SGC pin.
SGO can also be used as the reference voltage for the peripheral circuit. A capacitor of 0.1 mF or
more should be connected between SGO and GND.
SGC
+
–
C3
SG voltage
generating
circuit
+
–
SGO
To the
peripherals
To the internal
circuit
+
–
C6
Figure 6 Signal Ground
Digital input pin
The digital input pin contains a pull-up resistor. Therefore, supply the VIH voltage (VDD) to this
pin or open this pin to input "1". To input "0", supply the VIL voltage (GND) to this pin.
Upon power down (PON = "1"), this pull-up goes into a high-impedance state. Therefore, current
is not affected upon power down even though the VIL voltage remains connected to the digital
input pin.
12/21
¡ Semiconductor
MSM7715
Operation mode selection
By setting the MODE1 to MODE3 pins, an operation mode can be selected (see Table 1). The call
progress tone detector (CPT DET.) can be operated in the DTMF signal transmit mode and
modem mode. However, since the carrier detector is also used for the call progress tone detector,
only rectangular waveform output is available in modem mode. Set CPW = "1" when activating
the call progress tone detector in a modem mode.
Table 1 Operation Mode Table
MODE
Functional Block
Operation Mode
3
2
1
0
0
0
0
0
1
0
1
0
0
1
1
1
0
1
0
1
1
1
1
0 Modem
Analog loopback
1 mode Test (ALB)
mode
0
Remote digital
loopback (RDLB)
1
DTMF mode
DTMF
GEN.
DTMF signal transmit
DTMF
FSK
REC. MODEM
*
DTMF signal receive
CPT DET.
CPW = "1"
CPW = "0"
*
*
*
Normal Originate (O)
operation Answer (A)
*
*
*
*
O
*
*
A
*
*
O
*
*
A
*
*
* means active.
Note:
The carrier detecor may malfunction within 40 ms after the operating mode is changed
from the DTMF or power down mode to the modem mode.
Therefore, ignore an output signal from CD and RD during this period of time.
DTMF mode setting procedure after power-on or after releasing power-down mode
The following is a recommendable procedure to use DTMF mode after power-on or after
releasing power-down mode.
(1)
Put power-on or release power-down mode.
(2)
Set DTMF signal transmit mode. PON="0", TEN="1"
(3)
Wait more than 20 ms, VDD must be more than 2.5 V after this wait time.
(4-1)
In the case of DTMF receive, set DTMF signal to receive mode.
(4-2)
In the case of DTMF transmit, it is possible control transmit enable (TEN).
Modem mode setting procedure after power-on
The following is a recommendable procedure to use Modem mode after power-on.
(1)
Power on.
(2)
Set PON="1", TEN="1" and RS="1". Set mode to be used.
(3)
More than 200 ms after VDD becomes more than 2 V, set PON="0".
(4)
Wait more than 20 ms. VDD must be more than 2.5 V after this wait time.
(5)
It is possible to control transmit output. Ignore an output signal from CD and RD of
more than 40 ms which includes the wait time of term (4).
13/21
¡ Semiconductor
MSM7715
Modem signal flow
Figure 7 shows the signal flow during normal modem operation.
AIN
Line
AOUT
Receive filter
Demodulator
Transmit filter
Modulator
RD
Received data
Transmitted data
TD
Figure 7 Signal Flow in Normal Operation
The MSM7715 uses the analog loopback test (ALB) mode and remote digital loopback test
(RDLB) mode as the modem testing functions. In these test modes, the signal flow shown in
Figure 8 is used. O (originate)/A (answer) in the test mode is the expression based on the
modulator side. In ALB mode, the transmit analog signal is input to the demodulator and can
be monitored as RD. In RDLB mode, the modem is configured as the remote modem in the RDL
test mode.
Data from the other modem that requested for RDL is returned to the other modem as a result
of echo-back.
AIN
RD
Receive filter
Demodulator
Transmit filter
Modulator
Received data
[ALB]
TD
Transmitted data
AOUT
AIN
Receive filter
Demodulator
Transmit filter
Modulator
RD
Received data
[RDLB]
AOUT
TD
Transmitted data
Figure 8 Signal Flow in Test Mode
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¡ Semiconductor
MSM7715
DTMF signal code
Sixteen types of DTMF transmit signals can be set by using DTG1 to DTG4. Also, sixteen types
of DTMF receive signals can be monitored by using DT1 to DT4. Table 2 shows the DTMF signal
codes.
Table 2 DTMF Signal Codes
Button
Low-group signal (Hz)
697
1
*
2
*
3
*
770
852
941
*
6
1633
*
*
*
*
7
*
8
*
9
*
*
*
*
0
*
*
*
#
D
1477
*
*
C
1336
*
5
B
1209
*
4
A
High-group signal (Hz)
*
*
*
*
*
*
*
*
DT4
DT3
DT2
DT1
DTG4 DTG3 DTG2 DTG1
0
0
0
1
0
0
1
0
0
0
1
1
0
1
0
0
0
1
0
1
0
1
1
0
0
1
1
1
1
0
0
0
1
0
0
1
1
0
1
0
1
0
1
1
1
1
0
0
*
1
1
0
1
*
1
1
1
0
*
1
1
1
1
*
0
0
0
0
15/21
¡ Semiconductor
MSM7715
Microcontroller interface
By externally connecting DT1 to DT4 and DTG1 to DTG4 respectively, a 4-bit bus can be
configured (Fig 9).
In DTMF signal transmit mode, DT1 to DT4 enter a high-impedance state and this 4-bit line is
used to set the DTMF code against DTG1 to DTG4. The bus data is latched at the falling edge of
TEN.
In DTMF signal receive mode, DT1 to DT4 enter an output state. The 4-bit bus line is used as the
output of the DTMF code from DT1 to DT4 to the microcontroller. Latch this bus data at the rising
edge of SP.
In modem mode, DT1 to DT4 enter a high-impedance state. This 4-bit bus line is pulled up by
the pull-up resistor in DTG1 to DTG4.
In power-down mode (PON = "1"), DT1 to DT4 enter a high-impedance state. Since the pull-up
resistors in DTG1 to DTG4 also enter a high-impedance state, potential of this 4-bit bus line
becomes unstable from the MSM7715.
DT1
DT2
Microcontroller
DTMF Receiver
DT3
DT4
DTG1
DTG2
DTG3
DTMF Generator
DTG4
Figure 9 Microcontroller Interface Example
16/21
¡ Semiconductor
MSM7715
Setting the transmit signal level
4dB
AOUT
VAO
+
–
RC-LPF
GAT2
C4
R1
GAT1
R3
R2
DTO
MOD
DTMF
Generator
Modulator
R1, R2, R3 ≥ 20 kW, R1 £ R2, R1 £ R3
Figure 10 Setting the Transmit Signal Level
The modem’s modulated analog signal and DTMF signal are not transmitted at the same time.
The signal to be transmitted is determined by the selected operation mode. This device provides
the pins for individual setting of transmit signal levels.
VAOM: Level of the modem signal at the AOUT pin when R1 = R2 (dBm)
VAODT: Level of the DTMF signal at the AOUT pin when R1 = R3 (dBm)
When external resistors (R1, R2, R3) are changed, the signal level at AOUT is as follows:
VAO (modem) = 20 ¥ log (R1/R2) + VAOM
VAO (DTMF) = 20 ¥ log (R1/R3) + VAODT
However, to avoid distorted output, R1 ≤ R2 and R1 ≤ R3 are needed. In circuit design, R1 = R2
or R1 = R3 with 5% tolerance is permitted.
C4 is a component in the first order LPF for suppressing the out-of-band output noise. Select a
value C4 in such a way that cutoff frequency FC determined by R1 and C4 will be approximately
8 kHz.
C4 = 1/ (2p ¥ R1 ¥ FC)
17/21
¡ Semiconductor
MSM7715
External adjustment of the carrier detection level
11
R4
12
R5
6
VR1
VR2
SG
VREF
r1
r2
COMP
R4 + R5 ≥ 20 kW
r1 : 300 kW, r2 : 600 kW
Figure 11 External Adjustment of the Carrier Detection Level
The carrier detection level is determined by the resistance ratio between the MSM7715's internal
resistors r1 and r2, unless external resistors R4 and R5 are connected.
By connecting external resistors R4 and R5, the detection level can be adjusted. However, the
width of hysteresis cannot be changed.
Ra = R4 ¥ r1/(R4 + r1), Parallel-connected resistance of R4 and r1
Rb = R5 ¥ r2/(R5 + r2), Parallel-connected resistance of R5 and r2
VON = 20 ¥ log (Rb/(Ra + Rb)) –40.5 (dBm)
VOFF = 20 ¥ log (Rb/(Ra + Rb)) –42.5 (dBm)
Caution:
r1 and r2 may vary in similar proportions over a 0.5 to 2.0 ¥ range, due to the lot
variation and temperature variation.
18/21
¡ Semiconductor
MSM7715
Analog Interface
C7
r4 4 dB
Line
R8
–
+
AMP2
600 W : 600 W
R10
600 W
–
+
AMP1
r3
C8
R7
AOUT
R6
R14
R13
–
+
C9
AIN
–
+
+
–
VT
VR
R9
R15
SGO
R11
R12
SG
R15≥60 kW
Figure 12 Analog Interface Circuit Example
When R1 = R2 in the modem mode, the AOUT output level is at its maximum value of about –9
dBm. When R1 = R3 in DTMF mode, the AOUT output level is at its maximum value of –11 dBm
(sum of the low group and high group). To increase the transmit output level in the line to a high
level, use an external amplifier (AMP1).
The receive signal levels can be adjusted by the values of R13 and R14.
Clock noise of about –70 dBm will be generated from AOUT as out-of-band noise. (Clock noise
has a frequency of 27.965 kHz and its odd harmonics.) The clock noise level is nearly always
constant even if the output level of AOUT is lowered by varying the values of resistors R1 to R3
that are connected to GAT1, GAT2, DTO, and MOD. Therefore, to suppress this noise output to
the line, build a LPF at the AMP1. Note, however, that setting the cutoff frequency of the LPF
too low affects the output signal level.
Note that too large a time constant determined by the values of C9 and R15 allows the longer time
required for reaching a stable DC level, which may result in the violation of specification for the
DTMF signal receive output delay time.
Example: R15=100 kW, C9=0.022 mF.
Larger circuit-return levels of the transmit signal to the AIN pin can cause receive data errors.
If the line impedance is equal to the R10 impedance, R8=R9 can not induce the circuit-return
levels of the transmit signal to the AIN pin.
The peripheral circuits should be designed so that the circuit-return level, including variations
of the line impedance, of the transmit signal to the AIN pin is –9 dBm or less.
19/21
¡ Semiconductor
MSM7715
APPLICATION CIRCUIT
SP
PON
R12
C8
R6
Positive Supply
AOUT
R1
GAT2
R2 MOD
R3 DTO
DT4
DT3
DT2
DT1
CP
CD
RD
CLK
VR1
X1
GND
ICTA
ICTB
DTTIM
MODE1
MODE2
MODE3
C1
CPW
DTG1
DTG2
DTG3
C2
X2
VR2
DTG4
TEN
TD
RS
C4
SGC
GAT1
VDD
C3
SGO
AIN
C6
–+
C5
R15
C9
–
+
R7
R14
C7
–
+
R8
R13
R11
–
+
R10
R9
Line
Microcontroller
20/21
¡ Semiconductor
MSM7715
PACKAGE DIMENSIONS
(Unit : mm)
QFP44-P-910-0.80-2K
Mirror finish
Package material
Lead frame material
Pin treatment
Solder plate thickness
Epoxy resin
42 alloy
Solder plating
5 mm or more
Package weight (g)
0.41 TYP.
Notes for Mounting the Surface Mount Type Package
The SOP, QFP, TSOP, SOJ, QFJ (PLCC), SHP and BGA are surface mount type packages, which
are very susceptible to heat in reflow mounting and humidity absorbed in storage.
Therefore, before you perform reflow mounting, contact Oki’s responsible sales person for the
product name, package name, pin number, package code and desired mounting conditions
(reflow method, temperature and times).
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