ML145442 Datasheet, PDF (4/11 Pages) LANSDALE Semiconductor Inc. – Single-Chip 300-Baud Modem

ML145442, ML145443
LANSDALE Semiconductor, Inc.
3.579 MHz ± 0.1%
8
9
V _DD
RTLA
20
Xout
TLA
17
Xin
11
TxD
TxA
15
RxA2
TEST
INPUT
ML145442
600 Ω
ML145443
600 Ω
16 _RxA1
RxD ⁵
TEST _CDT
FB
OUTPUT ₄
10
0.1 µF
0.1 µF
Din
Dout
CCDT
CFB
Figure 1. AC Characteristics Evaluation Circuit
Table 1. Bell 103 and CCITT V.21
Frequency Characteristics
Originate Mode
Answer Mode
Data
Transmit Receive Transmit Receive
Bell 103 (ML145443)
Space
1070 Hz 2025 Hz 2025 Hz 1070 Hz
Mark
1270 Hz 2225 Hz 2225 Hz 1270 Hz
CCITT V.21 (ML145442)
Space
1180 Hz 1850 Hz 1850 Hz 1180 Hz
Mark
980 Hz 1650 Hz 1650 Hz 980 Hz
NOTE: Actual frequencies may be ±5 Hz assuming 3.579545 MHz
crystal is used.
MAXIMUM LEVEL OF OUT–OF–BAND ENERGY
RELATIVE TO THE TRANSMIT CARRIER LEVEL INTO 600 Ω (kHz)
0 2 3.4 4
16
64
256
0
PIN DESCRIPTIONS
VDD
Positive Power Supply (Pin 6)
This pin is normally tied to 5.0 V.
VSS
Negative Power Supply (Pin 12)
This pin is normally tied to 0 V.
VAG
Analog Ground (Pin 19)
Analog ground is internally biased to (VDD – VSS)/2. This
pin must be decoupled by a capacitor from VAG to VSS and a
capacitor from VAG to VDD. Analog ground is the common bias
line used in the switched capacitor filters, limiter, and slicer in
the demodulation circuitry.
TLA
Transmit Level Adjust (Pin 20)
This pin is used to adjust the transmit level. Transmit level
adjustment range is typically from –12 dBm to –9 dBm. (See
Legacy Applications Information.)
TxD
Transmit Data (Pin 11)
Binary information is input to the transmit data pin. Data
entered for transmission is modulated using FSK techniques. A
logic high input level represents a mark and a logic low repre-
sents a space (see Table 1).
TxA
Transmit Carrier (Pin 17)
This is the output of the line driver amplifier. The transmit
carrier is the digitally synthesized sine wave output of the modu-
lator derived from a crystal oscillator reference. When a 3.579
MHz crystal is used the frequency outputs shown in Table 1
apply. (See Legacy Applications Information.)
–20
–25
15 dB/OCTAVE
–55
–60
Figure 2. Out–of–Band Energy
ExI
External Input (Pin 18)
The external input is the non–inverting input to the line driver.
It is provided to combine an auxiliary audio signal or speech
signal to the phone line using the line driver. This pin should be
connected to VAG if not used. The average level must be the
same as VAG to maintain proper operation. (See Legacy
Applications Information.)
DSI
Driver Summing Input (Pin 1)
The driver summing input may be used to connect an external
signal, such as a DTMF dialer, to the phone line. A series resis-
tor, RDSI, is needed to define the voltage gain AV (see Legacy
Applications Information and Figure 6). When applying a signal
to the DSI pin, the modulator should be squelched by bringing
SQT (pin 14) to a logic high level. The voltage gain, AV, is cal-
culated by the formula AV = –Rf/RDSI (where Rf≈ 20 kΩ). For
example, a 20 kΩ resistor for RDSI will provide unity gain (AV
= –20 kΩ/20 kΩ = –1). This pin must be left open if not used.
RxD
Receive Data (Pin 6)
The receive data output pin presents the digital binary data
resulting from the demodulation of the receive carrier. If no car-
rier is present, CD high, the receive data output (RxD) is
clamped high.
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