ML4669CH Просмотр технического описания (PDF) - Micro Linear Corporation

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ML4669CH

10BASE-FL to 10BASE-T Converter

Micro Linear Corporation 

ML4664/ML4669

SYSTEM DESCRIPTION (Continued)

Link test pulses that do not occur within at most 25 to

150ms of each other are not considered consecutive.

In addition, detected pulses that occur within a time

between 2 to 7ms of a previous pulse will be considered

as noise by the link test circuitry, and will reset the count

of consecutive link pulses to zero.

If the ML4664 enters the link test fail state, both link

pulses at the twisted pair transmitter, and idle at the

optical transmitter will continue to be sent. Data will not

be sent at either transmitter.

If the ML4669 enters the link test fail state, idle will not

be sent at the optical transmitter. Data will not be sent at

either transmitter. However, link pulses may still be sent

at the twisted pair transmitter, depending on the optical

inputs. See Table 1.

POLARLITY CIRCUITRY

The ML4664/ML4669 offers automatic polarity correction.

The POLDIS pin is used to report the status of the receive

pair polarity. This pin is high when the polarity is correct,

and low when the polarity is reversed. If this pin is

grounded, the polarity correction circuit is disabled.

Polarity Detection — The internal circuitry uses the start

of idle signal to determine the receive polarity. With the

correct receive polarity, the Start of Idle signal (the end of

the frame) will remain above 300mV for more than

160ns. If the polarity is reversed, the Start of Idle signal

will end with a negative voltage.

The POLDIS status pin is updated only when four

consecutive frames are received with the same Start of

Idle polarity. In the case where the part is powered up

with the receive polarity reversed and no frames are

received, the part will go into link test fail without

reflecting a reverse polarity condition. If five consecutive

revised link pulses are then received, the polarity will

reverse and the device will come out of Link Test Fail.

TP TRANSMISSION

The TP transmit function consists of detecting the

presence of data from the OP inputs, OPINP and OPINN

and driving that data onto the transmit twisted pair

(TPOUTP, TPOUTN). A positive signal on the OPINP lead

relative to the OPINN lead will result in a positive signal

on the TPOUTP lead of the chip with respect to the

TPOUTN lead.

Before data will be transmitted onto the twisted pair from

the OP inputs, it must exceed the squelch requirements

for the OP inputs. The OP squelch circuit serves the

function of preventing any noise from being transmitted

onto the twisted pair.

The output stage of the transmitter is a current mode

switch which develops the output voltage by driving

current through the terminating resistor and the output

filter. The transmitter employs a center tap 2:1 transformer

where the center tap is tied to VCC (+5V). While one pin

of the transmit pair (TPOUTP, TPOUTN) is pulled low, the

other pin floats. The output pins to the twisted pair wires,

BINARY

TxTP+

TxTP–

0

1

1

1

0

0

1

1

0

OUTPUT AFTER

TRANSMIT FILTER

INPUT INTO

RECEIVER

Figure 9. Transmit Pre-Equalization Waveform

10

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