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LANSDALE Semiconductor, Inc.

ML145442, ML145443

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.)

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.

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.

15 dB/OCTAVE

256

64

16

3.4 4

2

0

0

–20

–25

–55

–60

MAXIMUM LEVEL OF OUT–OF–BAND ENERGY

RELATIVE TO THE TRANSMIT CARRIER LEVEL INTO 600

Ω (kHz)

Figure 2. Out–of–Band Energy

TEST

INPUT

600

Ω

600

Ω

VDD

RTLA

20

17

15

16

TEST

OUTPUT

4

CDT

RxA1

CCDT

CFB

0.1

µF

10

FB

RxD

5

11

Dout

Din

TxD

Xin

9

8

Xout

TLA

TxA

RxA2

ML145442

ML145443

0.1

µF

3.579 MHz ± 0.1%

Figure 1. AC Characteristics Evaluation Circuit

Issue b