DS1877 datasheet(13/65 Pages) MAXIM

13 / 65 page

SFP Controller for Dual Rx Interface

Detailed Description

The DS1877 integrates the control and monitoring func-

tionality required in an SFP or SFP+ system. The device

is specifically designed for a dual-receiver SFP module.

Key components of the device are shown in the Block

Diagram and described in subsequent sections.

DACs During Power-Up

On power-up, the device sets the DACs to high imped-

ance. After time tINIT, the DACs are set to an initial con-

dition set in EEPROM. After a temperature conversion is

completed and if the VCC LO alarm is enabled, an addi-

tional VCC conversion above the customer-defined VCC

LO alarm level is required before the DACs are updated

with the value determined by the temperature conversion

and the DAC LUT. See Figure 1.

Quick-Trip Timing

As shown in Figure 2, the device’s input comparator is

shared between two LOS comparisons. The comparator

polls the alarms in a multiplexed sequence. The com-

parator checks the LOS (RSSI1_ and RSSI2_) signals

against the internal reference. Depending on the results

of the comparison, the corresponding alarms and warn-

ings are asserted or deasserted. Any QT alarm that is

detected by default remains active until a subsequent

comparator sample shows that the condition no longer

exists.

Table 1. Acronyms

Figure 1. Power-Up Timing

Figure 2. Quick-Trip Sample Timing

VCC

VPOA

DAC

SETTINGS

HIGH IMPEDANCE

OFF STATE

LUT VALUE

500µs

tINIT

QUICK-TRIP SAMPLE TIMES

LOS2

LOS1

LOS2

tREP

ACRONYM

DESCRIPTION

ADC

Analog-to-Digital Converter

AGC

Automatic Gain Control

APC

Automatic Power Control

APD

Avalanche Photodiode

ATB

Alarm Trap Bytes

DAC

Digital-to-Analog Converter

LOS

Loss of Signal

LUT

Lookup Table

Nonvolatile

Quick Trip

TIA

Transimpedance Amplifier

ROSA

Receiver Optical Subassembly

SEE

Shadowed EEPROM

SFF

Small Form Factor

SFF-8472

Document Defining Register Map of SFPs

and SFFs

SFP

Small Form Factor Pluggable

SFP+

Enhanced SFP

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