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MTC-3058

Data Sheet

Preliminary

Application Specific Standard Products

Features

• Line Driver Receiver for Power-

Line Carrier Com-munications

• Supports most used Modula-

tion Schemes

• Very Low Distortion

• Low Standby Power Mode

• Integrated Noise Filter

• Integrated Zero-Cross

Detector and LED Driver

• "Babbling" Detection and

Thermal Overload Protection

Description

The MTC-3058 is a line driver / recei-

ver specially designed for Power Line

Carrier applications (PLC - data trans-

mission over the mains wiring). Though

designed specifically for the exchange

of data between intelligent electricity

meters and the utility supplier, the devi-

ce offers sufficient flexibility to be used

in domestic or other communications

systems, which also use PLC transmis-

sion (e.g. home automation buses

etc...). In order to comply with the very

strict European standards governing the

frequency spectrum of such PLC sys-

tems, the MTC-3058 has exceptionally

low distortion in the transmit path, so

reducing higher frequency harmonics.

NEGINP

ANSIGOUT

CROSS1

ANZCIN

VDD

VSS

ANTXIN

OUTF

CAPMMV

TXON

VREF

Fig.1: Device Pinout

CALTX

CURSENSE

ANRXOUT

AGND

The MTC-3058 device consists of a line

transmitter driver including an AGC

feedback section, a line receiver plus

limiter, a LED driver, a thermal shut-

down protection block, a zero-crossing

detector and a reference voltage gener-

ator. The block diagram in Fig.2 shows

the general configuration of the MTC-

3058. The MTC-3058 forms the OSI

“layer 1” interface between a suitable

MODEM device and the mains net-

work.

MTC

3058

ANSIGIN

VSS

DGND

OPTIN

OPTOUT

TXEN

MTC-3058

325pF

16.5K

OUTF

1.66K

TXIN

22.6K

2.2K

325pF

ANTXIN

VDD

AGND

DGND

NEGINP

Filter Opamp

Driver Opamp

ANSIGOUT

0.47µF

2:1

VSS

MTC -3058

TSD

Thermal

Shutdown

VSS

1nF

5...20

ANRXOUT

Clamping

ANSIGIN

VREF

CURSENS

CALTX

OPTOUT

Clamping

Led Driver

OPTIN

MMV

TSD

BIAS Gen.

Detect

ANZCIN

TXEN

2.2µF

TXON

CapMMV

CROSS1

Fig.2: MTC-3058 General Block Diagram

Packaging

The MTC-3058 is supplied in a 24 pins

plastic dual in line, 300mills (PDIL). The

relatively high power dissipation

requires that the two center pins on

each side all be connected to VSS,

preferably with a large area of track so

as to minimize thermal resistance. The

high peak power which can be dissipa-

ted by the MTC-3058 in normal opera-

tion also leads to specific conditions for

the reliability of the device. (See section

"Quality and Reliability")

MTC-3058

Pin Description

Name

NEGINP

ANSIGOUT

CROSS1

ANZCIN

VDD

VSS

ANTXIN

OUTF

CAPMMV

TXON

VREF

TXEN

OPTOUT

OPTIN

DGND

VSS

ANSIGIN

AGND

ANRXOUT

CURSENS

CALTX

Type

ANAIN

ANAOUT

DIGOUT

ANAIN

POWER

ANAIN

ANAOUT

ANAIN

DIGIN

ANAOUT

DIGIN

ANAOUT

DIGIN

POWER

ANAIN

POWER

ANAOUT

ANAIN

ANAOUT

Description

Negative input of TX driver opamp

Transmit driver output

Zero-cross detector output

Zero-cross detector input

Positive power supply

Negative power supply

Transmit filter input

Transmit filter output

MMV timing capacitor input

Transmit driver enable (direct control)

Buffered reference voltage output

Power down control signal

Transmit driver enable (through MMV)

LED driver output

LED driver control signal

Digital ground

Negative power supply

Receiver analog input

Analog ground

Received analog output

Current sensing input

Transmit AGC output

Nominal Pass-Band

500

0dB

10K

530K

freq. (Hz)

-20dB

RxAtt500Hz

RxAtt8MHz

Fig.3: Filter Characteristic of Receive and Current-sense Path

MTC-3058

Functional Description

Transmit Function

The transmit section can be divided into

two paths:

- In the feed forward path, it consists

of an opamp which will be configu-

red by the user as a second order

bandpass filter, and a class AB line

amplifier.

- In the feedback path, it consists of a

highpass and a lowpass filter section

which converts the line coupling trans-

former primary coil current into a cali-

bration voltage used for AGC pur-

poses by the modem device.

The Forward Transmission Path

The external signal from the modem,

ANTXIN, is first fed to a second order

bandpass filter in order to decrease the

second order harmonic distortion.

Because most of the characteristics of

the filter are defined by the external

components, the MTC-3058 can be

adapted to a wide range of standards

and modulation frequencies. After filte-

ring, the signal is fed to a class AB line

amplifier. This amplifier drives the pri-

mary coil of an external transformer (at

a frequency of 72kHz or 82 kHz typi-

cal). The secondary coil of this transfor-

mer is AC coupled to the mains. The

transformer has a ratio of 2 to 1. A

resistor is placed in series with the pri-

mary coil of the transformer and the

analog ground (AGND) . This external

resistor is used to sense the current

through the transformer coil and to

convert it to a voltage. This voltage is

then fed to the input pin CURSENS of

the feedback path. See block diagram.

The Feedback Path: Automatic

Gain Control (AGC)

To overcome distortion while maximiz-

ing the transmitted power, the amplitu-

de of the signal ANTXIN can be mea-

sured and externally regulated by

means of a control voltage CALTX

generated by MTC-3058. The voltage

at pin CURSENS is used for this purpo-

se. It is first fed to an AC coupled

bandpass filter, consisting of a first

order lowpass filter section followed by

a first order highpass filter section. The

nominal cut-off frequencies are 10kHz

and 530kHz (±45%), as shown in

Fig.3. The signal is filtered to reject all

noise induced by the mains distribution

line in the low frequency range, and is

then internally clamped for protection

purposes. The buffered signal is avai-

lable at pin CALTX, and is used as the

external amplitude control.

The TXEN Signal: (Transmit

Enable)

With the external control signal TXEN,

MTC-3058 can be put into its transmit

or its receive mode. If TXEN is made

logical zero (low voltage), the transmit

mode is activated. All functional blocks

perform their normal function, including

the receive path. If TXEN is made logi-

cal one (high voltage), the receive

mode is activated. In this mode, the

transmit section is powered down and

disconnected from the line. This is esta-

blished by putting the filter opamp and

the line driver into a high impedant

state. The calibration path is not affec-

ted by this action and stays operatio-

nal. To guarantee disconnection from

the line due to malfunction of one or

more modules, TXEN does not directly

control the transmit/receive mode, but

is first passed through a retriggerable

monostable multivibrator (called MMV),

used as a watchdog timer. (Continuous

transmission over a time would cause

the heat generated by the MTC-3058

to build up, eventually causing the ther-

mal shutdown protection to operate).

Transmit Time Watchdog - MMV

The MMV circuit consists of an external

capacitor at pin CapMMV, which is

charged with a constant current, and

who’s voltage is compared with the

internal reference Vref. The configura-

tion of the MMV and the relevant

timings are shown in figures 4 and 5.

To retrigger the MMV, the output is

rapidly discharged using an internal

pulldown transistor. The pulldown tran-

sistor is controlled by a filtered and

delayed signal, derived from the input

TXEN. The filtering plus delay prevents

switching due to short spikes. If TXEN is

high (receive mode) during this delay

time, the output of the MMV is reset

and the outputs of the filter opamp and

line driver are put in a high impedant

state. If TXEN goes low, the MMV is

triggered and the voltage on pin

CapMMV starts to rise. Under normal

conditions, the transmission duration is

always shorter than the total MMV

time, so the voltage on CapMMV will

not reach the trigger level of the com-

parator and no time-out will occur. If

however TXEN stays low beyond the

MMV time, the voltage on pin

CapMMV will increase above the refe-

rence voltage Vref of the comparator

and a time-out will occur. When a time-

out occurs, MTC-3058 is forced into

receive mode, independent of the state

of TXEN. If TXEN is made high again,

the capacitor at pin CapMMV is dis-

charged rapidly, and normal operation

is restored. To limit the discharge time

and current, the voltage at pin

CapMMV is clamped to a level just

above the internal reference.

Receive Function

The receive path consists of an AC cou-

pled first order bandpass filter, which

reduces the 50Hz component and

other noise from the line. The filter has

the same characteristics as the TXSense

filter. The filter is followed by a limiting

stage, which clamps the amplitude on

the output pin RXOUT to a safe value.

The receive path is always operating,

independent of the state of TXEN.

MTC-3058

Vref

MMV out

to logic

CapMMV

Cext

TXEN

DGND

TdisdelMMV

Fig.4: Principle of MMV

TXEN

<3s

3s…5s

INTERNAL

MMV output

enabled

VREF

charging

VcapMMV

TdisdelMMV

anti-spike delay

2 µs ... 10 µs

Fig.5: Timing of MMV Circuit

disabled

enabled

dis-

abled

charging

discharging

Clamping