MTD492 [ETC]

Coaxial Transceiver Interface; 同轴电缆收发器接口


型号：	MTD492
厂家：	ETC
描述：	Coaxial Transceiver Interface 同轴电缆收发器接口
文件：	总8页 (文件大小：182K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

MYSON

TECHNOLOGY

MTD492

Coaxial Transceiver Interface

FEATURES

•

Compatible with IEEE 802.3 10Base5 (Ethernet) and 10Base2 (Cheapernet).

Internal AUI squelch circuitry for noise rejection.

Transmission IDL detection at end of packet and dribble bit rejection window.

Reception dribble bit rejection window.

•

Reception and transmission mode collision detection.

Extended collision detection to turn off receiving path.

CD heartbeat externally controllable.

•

Advanced low-power, high-performance CMOS technology.

ESD protection greater than 2000 Volts.

•

16-pin PDIP and 28-pin PLCC packages.

GENERAL DESCRIPTION

The MTD492 transceiver integrates the coaxial cable interface functions of the Medium Attachment Unit

(MAU) in Ethernet or Cheapernet LAN applications. In an Ethernet 10Base5 network, MTD492 is mounted

on the thick Ethernet coaxial cable and connects to a station through an AUI cable. For Cheapernet

applications, MTD492 is connected to the Cheapernet coaxial cable through a BNC connector and is

usually mounted on the LAN adapter in a station.

BLOCK DIAGRAM

COAX

RX+

RX-

AUI

DRIVER

HIGH PASS

EQUALIZATION

C O M

LOW PASS

FILTER

FXI

CD+

CD-

AUI

DRIVER

CARRIER

SENSE

GND

LOW PASS

FILTER

TX+

TX-

125

10K

XMT

COLLISION

V E E

CDS

LOW PASS

FILTER

RECV

TXO

WAVEFORM

SHAPING

DC/AC

SQUELCH

CLK

10MHz

OSC

WATCH DOG

TIMER 26ms

JABBER RESET

TIMER 0.4sec

XMTSQ

VEE

RR+

REFERENCE

CIRCUIT

RECEIVE

STATE

MACHINE

TRANSMIT

STATE

MACHINE

RR-

HBE

This datasheet contains new product information. Myson Technology reserves the rights to modify the product specification without notice. No

liability is assumed as a result of the use of this product. No rights under any patent accompany the sale of the product.

MTD492 Revision 3.5 01/07/1997

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TECHNOLOGY

MTD492

1.0 CONNECTION DIAGRAM

VEE

VEE(NC)

VEE

CD+

CD-

RX+

VEE

RX-

TX+

TX-

CDS

TX0

RXI

VEE

RR-

RR+

GND

HBE

MTD492V

28 PIN PLCC

MTD492N

16 PIN PDIP

VEE

VEE(NC)

VEE

VEE(NC)

RR-

2.0 PIN DESCRIPTIONS

Name I/O PDIP PLCC

Description

Pin#

TX+,TX-

HBE

7,8

13,14

Transmission Data Input. A balanced differential line receiver which

receives inputs from the off-chip Manchester Code Converter(MCC) to

the Transmitter. The common mode voltage on TX+ is set internally .

Heartbeat Enabler. The CD heartbeat test is enabled when HBE is

connected to Ground and disabled when HBE is connected to VEE.

This pin is internally biased at 0.5 VEE. Test mode is enabled if this

pin is left floating or biased in the range of -3.5V to -5.5V. Jabber is

disabled in test mode. Exiting the jabber disable mode requires at

least jabber reset time.

RR+,RR-

RXI

11,12 18,19

External Resistor. A 1kΩ/1% resistor should be connected across

these pins to correctly set internal operating currents. RR+ is

internally shorted to GND.

Network Receiving Input. Should be connected to the COAX center

conductor. Signals meeting receiver squelch limits are recovered and

output on RX+. RXI also detects the collision voltage level.

Collision Detection Sense. Connects directly to the COAX

shield, providing a reference for the collision detection voltage

level for reception-mode detection. An external bias network can be

used to shift the detection threshold for transmission-detection mode.

Collision Output. A balanced differential line driver drives this

output pair from the collision detection circuitry. A 10MHz signal from

the internal oscillator is transferred to these outputs in the event of

collision, excessive transmission (jabber), or during heartbeat

condition. These outputs are open sources, and pull-down resistors of

510Ω to VEE are required. To minimize power dissipation, both open

source outputs are disabled during idle condition, allowing the

common mode on the pull-down resistors to be pulled to VEE.

CDS

CD+,CD-

1,2

2,3

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MTD492

RX+,RX-

3,6

4,12

Reception Data Output. A balanced differential output drives the

data

recovered from the network to the MCC. These outputs are also open

sources, and pull-down resistors of 510Ω to VEE are required. These

pins are biased at -2V during idle time. When an extended period of

collision condition happens, the receiving path is disabled. Any

interruption of collision will re-enable the receiving path.

Transmission Output. Should be connected to the coaxial cable via

either one (Cheapernet) or 2 serial isolation diodes (Ethernet).

Positive Supply Pin(Ground). Should be connected to the COAX

shield.

TXO

GND

VEE

4,5, 5, 6, 7,

13 8, 9, 10,

11, 20,

Negative Power Supply. -9 Volts. A 0.1µF decoupling capacitor

must be connected across GND and VEE as close to the device as

possible.

21, 22,

23, 24,

3.0 FUNCTIONAL DESCRIPTIONS

3.1. Transmission Path

The transmission data is input from TX+/- pins differentially. In general, this differential signal is coupled

through an AUI isolation transformer. In the MAU design, it is preferable that an equivalent 78 Ohm load be

placed across these 2 pins for proper loading for the signal source. Improper load termination may cause

excess undershoot at the end of the packet, which causes the dribble bit to be transmitted erroneously.

The transmission signal is first checked against the on-chip DC/AC squelch condition. If the signal is

greater than the squelch threshold (-175 to -300 mV) and the width is wider than 17 nsec, the squelch is

turned off. The squelch remains off until the DC squelch condition is not met or an end-of-packet IDL is

detected (at the end of the packet, data remains at 1 for longer than 175 nsec). Once IDL is detected,

MTD492 provides a 0.8 usec rejection window that prevents dribble bit transmission at the AUI interface.

When the squelch is off, the transmission path is enabled and data is fed into a waveform shaping circuit

followed by the transmission output buffer. The waveform shaping function controls the output rise/fall time

between 20nsec and 30 nsec, and minimizes the mismatch between the rise/fall time. MTD492 provides a

current source output that should be connected to the coaxial cable through at least one isolation diode.

When data is high, the output current is virtually zero (there is approximately less than 1mA output in this

state to maintain the linearity of the output buffer); when data is low, the output current peaks at around 80

mA. This provides an approximate 2V peak to peak swing on a 25 Ohm load. Due to the nature of

Manchester code, the average output DC current is half of the peak - 40 mA, i.e. 1V DC average on the

cable 25 Ohm load.

3.2. Reception Path

The signal on the coaxial cable is first buffered. The DC average of the signal is extracted by a low pass

filter. When the DC average exceeds the carrier sense threshold (Vcs), the reception data path is turned

on. The signal goes through a high pass filter for equalization of high frequency loss on the cable and then

is compared with its center value. The comparator output is amplified by the AUI driver to provide adequate

driving for the RX+/- output.

The end of the packet is determined by 2 conditions. If the received data is high longer than 175nsec or the

DC average does not meet the carrier sense threshold, the reception data path is turned off. MTD492 then

appends the IDL pulse to the end of the packet. A rejection window of 1 usec that blocks the data reception

path is also turned on.

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MTD492

The RX+/- output pin is driven by a source follower. Therefore, an external pull-down load is required for

these 2 pins. During idle state, RX+/- is biased at around -1.5V.

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MTD492

3.3. Collision Detection Path

In 10Base2 and 10Base5, a collision condition is determined by the DC level on the cable. The DC average

is extracted by a low pass filter. The output of the filter is compared with an internally set threshold (Vcd) to

determine the collision condition. The internal threshold is set for the reception-collision mode. By

definition, MTD492 will detect collision conditions caused by more than 2 stations simultaneously

transmitting.

The collision detection threshold can be shifted by applying a voltage to the CDS pin. This is typically done

by a resistor divider network between GND and VEE to implement the transmission-collision mode

detection. Transmission-collision differs from reception-collision in that transmission-collision will only

detect a 2-station collision if it is transmitting.

Once a collision is detected, MTD492 turns on the CD+/- pins. These 2 pins are also driven by source

followers, thus requiring external pull-down resistors. However, the followers are disabled during idle time,

and CD+/- will be pulled down to VEE and no current will flow through the external resistors.

Because Vcd is always larger than Vcs, when a collision occurs the reception path will also be turned on.

MTD492 implements an internal timer of 250 msec to detect the extended collision period. When a collision

condition period extends beyond this timer, the reception path is turned off. Any interruption of the collision

will reset the timer.

3.4. Reference and Control

The internal reference of MTD492 is generated by an on-chip bandgap circuit. An external resistor

connected between RR+ and RR- pins is used to set the reference current level. Typically, a precision 1K

Ohm resistor should be used. RR+ is internally shorted to GND, while RR- is biased at around -1.25V.

The heartbeat and jabber functions of MTD492 are implemented in the transmission state machine. The

heartbeat function is controlled by the HBE pin. MTD492 also provides a test mode that disables the jabber

function also controlled by the HBE pin. HBE has a 3-level input. It is biased internally at around -4.5V

(0.5Vee). When HBE is pulled high by a low value resistor (<4.7K), the heartbeat function is enabled; when

it is pulled low, the heartbeat is disabled. If it is driven to the mid-level or left floating, the jabber is disabled.

The exit of the jabber disable state takes about 0.5 sec (jabber reset time).

4.0 ABSOLUTE MAXIMUM RATINGS

DC Supply Voltage(VEE)

Input Voltage

Storage Temperature

Ambient Operating Temperature

ESD Protection except for Pin14

-12V

GND+0.3 to VEE-0.3V

-65 to 150 C

0 to 70 C

2000V

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5.0 ELECTRICAL CHARACTERISTICS (under operating conditions) (Note 1)

OPERATING CONDITIONS

DC Supply Voltage (VEE)

Operating Temperature

8.55-9.45V

o o

0 to 70 C

Parameter

Recommended Supply Voltage

Symbol

VEE

IEEidle

IEExmt

Irxi

Min

-8.55

Typ

-9.0

-25

-70

Max

Unit

-9.45

-35

Supply Current (all VEE pins) Non-transmission

Transmission

µA

-80

Receiver Input Bias Current (RXI)

-2

+25

Transmission Output DC Current (TXO)

Transmission Output AC Current (TXO)

Collision Threshold (Reception Mode)

Carrier Sense Threshold (RXI)

Itdc

Itac

+28

-1.45

-0.38

+500

-1.0

VEE

Itdc

-1.62

-0.52

+1500

-3.0

VEE

+40

-300

Vcd

-1.53

-0.45

Vcs

Differential Output Voltage (RX+,CD+)

DC Common Mode Output Voltage (RX+)

DC Common Mode Output Voltage (CD+) (Note 2)

Idle State Differential Offset Voltage(RX+,CD+)

Transmission Squelch Threshold(TX+) (Note 3)

Input Capacitance (RXI)

Vod

Vocrx

Voccd

Vob

-2.0

VEE

kΩ

Vts

-175

-225

1.5

Shunt Resistance - Non-transmission

Shunt Resistance - Transmission

Rrxi

100

Rtxo

Notes: 1. Testing is done under the testing load defined in Figure 6.

2. During an idle condition, Voc is pulled down to VEE to minimize the power dissipation across the

load resistors connected to CD+pins.

3. Tested under continuous 5MHz waveform that represents the preamble.

6.0 SWITCHING CHARACTERISTICS (under operating conditions) (Note 1)

Parameter

Reception Start-up Delay (RXI to RX+)

Reception Propagation Delay (RXI to RX+)

Differential Output Rise Time (RX+,CD+)

Differential Output Fall Time (RX+,CD+)

Receiver and Cable Total Jitter

Symbol

Tron

Trd

Trr

Trf

Trj

Ttst

Ttd

Ttr

Ttf

Ttm

Tts

Tton

Ttoff

Ttidl

Tcon

Tcoff

Min

Typ

2.5

+0.5

200

170

Max

Unit

bits

Transmission Start-up Delay

Transmission Propagation Delay

Transmission Rise Time (10%-90%) (TXO)

Transmission Fall Time (10%-90%) (TXO)

Ttr and Trf Mismatch

Transmission Skew(TXO)

Transmission Turn-on Pulse Width at Vts(TX+) (Note 4)

Transmission Turn-off Delay

Transmission IDL Detection Time (Note 5)

Collision Turn-on Delay

Collision Turn-off Delay

+3.0

260

200

130

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MTD492

Collision Frequency (CD+)

Collision Pulse Width (CD+)

Fcp

Tcp

Tcxd

Thon

Thw

Tja

8.5

100

0.6

0.5

200

1.1

1.0

12.5

300

1.6

1.5

MHz

µs

Extended Collision Detection Time (Note 6)

CD Heartbeat Delay (TX+ to CD+)

CD Heartbeat Duration(CD+)

Jabber Activation Delay(TX+ to CD+)

Jabber Reset Time-out (TX+ to TXO and CD+)

Tjr

300

420

550

Notes: 4. For a minimum pulse amplitude of > -300 mV.

5. IDL detection precedes the transmission turn-off by transmission propagation delay.

6. Time needed to detect an extended period of collision in order to turn off the reception path.

7.0 TIMING DIAGRAM

INPUT

TO RXI

50%

T_roff

T_ron

T_rd

T_rf

90%

10%

RX+

RX-

50%

T_rr

Figure 1. Reception Timing

TX+

TX-

50%

T_tidl

T_toff

V_ts

T_ton

T_tst

T_td

90%

10%

TXO

OUTPUT

50%

T_tf

T_tr

Figure 2. Transmission Timing

TX+

TX-

T_hon

T_hw

CD+

CD-

Figure 3. Heartbeat Timing

-1.75V

-1.2V

INPUT

to RXI

V_cd(max)

T_con

V_cd(min)

-6.8V

T_coff

1/F_cp

T_cp

CD+

CD-

Figure 4. Collision Timing

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MTD492

TX+

TX-

T_ja

TXO

T_jr

CD+

CD-

Figure 5. Jabber Timing

Ω

Receiver (RX⁺_-

)

TXO

Transmitter

Output

50 H*

Collision(CD⁺_-

Outputs

)

Ω

510

Ω

510

Ω

VEE

*: 50µH inductor is used for testing purposes. Pulse transformers with higher primary inductance are

recommended.

Figure 6. Test Loads

8.0 PACKAGE DIMENSION

312+/-12

100+/-20

350+/-20

R40

250+/-4

55+/-20

75+/-20

90+/-20

60+/-4

310Max

750+/-10

7Typ

15Max

35+/-5

15Max

115Min

15Min.

100Typ

18+/-2Typ

60+/-5Typ

MTD492 Revision 3.5 01/07/1997

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MTD492 [ETC]

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