SP506CF datasheet(11/30 Pages) SIPEX

11 / 30 page

SP505/6/7APN/03

SP505, SP506, SP507 Application Note

SP506 and SP507 Drive Capability

According to the ITU-T V.11 standard, the maximum

cable length for a differential V.11 transmission is

4,000 feet (~1,000 meters). However, the standard

also illustrates a derating graph of data rate versus

cable length. So actually in a real application, the

system would not be able to transmit 10Mbps over

the full 4,000 feet of Category 3 or similar type cable.

As cable parasitics add up over longer cable lengths,

capacitance and other affects will degrade the signal,

especially at higher frequencies.

The signal integrity depends mainly on the driver

output strength or "drivability" and parasitic

capacitance on the cable. RS-232 cabling is typically

50pF per foot, where as a good twisted pair type

cable for X.21, RS-449, EIA-530, or V.35 will

typically be 10pF per foot or less. Some better quality

cables will have 3-5pF per foot.

Using a typical setup with a TTC Fireberd 6000A Bit

Error Rate Tester (BERT) connected with our SP507

evaluation board as configured in Figure 8 below,

the driver output performance was characterized

over various cable lengths. The 6000A BERT

emulated the DCE, which provided the TXC clock

pulse from 1.544Mbps to 12Mbps. The clock waveform

was propagated through the serial cable to the SP507

evaluation board, which was configured as the DTE.

The clock signal was then "echoed" through the

TxCE (Transmit Clock Echo) driver across the cable

and back the BERT. The clock signal input to the

TxCE driver (CH3) and the differential driver output

are measured with a oscilloscope to observe driver

waveform integrity. The differential driver output

was measured at the other end of the cable (M1 =

A - B), as if the receiver would view the incoming

signal. The data stream was generated by the DCE

and was propagated through the SP507's RxC

receiver and TxCE driver. The BERT also records

the number of bit errors occurring during the infinite

1:1 data bit stream that is sent back through the cable.

Figure 8. SP507 Cable Length Versus Throughput Circuit Configuration

µF22µF

µF

27 26

MBRS140T3

VCC

VDD

C1-

C2-

VSS

C1+

C2+

µF

SP507CF

TxD

DTR

RTS

TxCE

RxD

RxC

CTS

DSR

DCD

SCT

µF

STEN

RREN

RTEN

Various GND pins (Refer to SP507 Datasheet)

TMEN

SCTEN

LLEN

RLEN

TTEN

+5V

LATCH

GND

+5V

Fireberd 6000A

Network/BER Tester

TxD

RxD

DTR

DSR

CTS

DCE (emulated)

DTE (Evaluation Board)

CH3

RTS

RxC

DCD

TxC

Notes: V.35 Mode selected.

Open Driver Inputs

are default as HIGH.

“1”

“0”

Signal GND

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