ML6680 datasheet(3/12 Pages) MICRO-LINEAR

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ML6680

PIN DESCRIPTION

PIN# NAME

FUNCTION

1, 28 XTAL1,

Crystal inputs. A 32.768kHz watch

XTAL2

crystal connected between these pins

provides timing for the fiber optic

insertion key signal. An external clock

can be used to drive XTAL1 while

grounding XTAL2. The frequency of

the external clock should be between

32.7kHz and 34.5kHz.

2VCC2

Positive 5V power supply.

3, 4

EQA, EQB Equalizer network pins. An external

combination of two resistors and a

capacitor connected at EQA and EQB

sets up the on-chip twisted pair

receive equalizer.

5, 6 TPINP/N

Receive twisted pair inputs. This

differential input pair receives

differential Manchester signals from

the coupling transformer (or PECL

compatible levels).

7, 8 PHTM1/2

Phantom drive/sense inputs/outputs. In

configuration 1, these pins are TTL

inputs from two external opto

isolators. They are low when phantom

power is present and high when

phantom power is removed. These

pins provide the phantom drive

current and are used to check for a

wire fault on the phantom circuits

when it is required in configuration 2.

In configuration 3, these pins are don’t

cares. In configuration 4, these pins

are low for normal operation, or any

or both of them is high to force the

ML6680 into the “Bypass State.”

GND2

Ground.

10, 11 TPOUTP/N Transmit twisted pair outputs. This

differential current output pair drives

differential Manchester signals into the

network coupling transformer and

transmit filter. Output edge rates are

controlled to allow use of a simpler

filter than would otherwise be

required. These outputs can be PECL

compatible with an external resistor

network.

TPINOK

Valid twisted pair input signal

indicator. It is an active low, open

collector LED driver. This output goes

low when the signal at TPINP/N meets

frequency and amplitude squelch

requirements. This input is tied to

ground for configurations 3 and 4 to

enable signal path switching.

PIN# NAME

FUNCTION

RTSETTP

Twisted pair transmit level set resistor

input. A precision resistor between

RTSETTP and VCC sets the amplitude

of the TPOUTP/N output.

VCC1

Positive 5V power supply.

INSERTED Insertion indicator. It is an active low,

open collector LED driver. In

configurations 1, 3 and 4 this output

goes low when the ML6680 is in the

“Insert State.” In configuration 2 this

output goes low when the ML6680 is

in the “Insert State” and no wire fault

is detected. This input is tied to ground

to disable the frequency squelch, and

to reduce the time constant of the

amplitude squelch of the optical input.

RTSETOP

A precision resistor between RTSETOP

and VCC sets the amplitude of the

OPOUT output.

OPINOK

Valid fiber optic input signal indicator.

It is an active low, open collector LED

driver. This output goes low when the

signal at OPINP/N meets frequency

and amplitude squelch limit for

received signals at TPINP/N.

OPVCC

Positive 5V power supply for fiber

optic LED driver.

OPOUT

Fiber optic LED driver output. The

fiber optic LED connects between this

pin and OPVCC.

OPGND

Ground for the fiber optic LED driver.

GND1

Ground.

KEYGEN

Key generation select CMOS input.

This input is low for configurations 2

and 3 of the general description, and is

high for configurations 1 and 4.

VDC

Offset correction time constant

capacitor input. An external capacitor

between this pin and QGND

determines the time constant of the

internal offset correction circuit for the

fiber optic quantizer.

QGND

Quantizer’s ground.

26, 25 OPINP/N

Receive fiber inputs. This pair of inputs

receive differential Manchester signals

from the fiber optic receiver/preamp

and present them to the on-chip fiber

optic quantizer. These inputs should

be capacitively coupled to the input

source. The input resistance is

approximately 1.3k

Ω.

QVCC

Quantizer’s positive 5V power supply.

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