DS1876 datasheet(13/69 Pages) MAXIM

13 / 69 page

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SFP Controller with Dual LDD Interface

only difference is that the DS1876 already has deter-

mined the present temperature, so the tINIT time is not

required for the DS1876 to recall the APC and MOD

set points from EEPROM. See Figure 1.

DACs as a Function of Transmit Disable

(TXD1, TXD2)

If TXD1 or TXD2 are asserted (logic 1) during normal

operation, the associated outputs are disabled within

tOFF. When TXD1 or TXD2 are deasserted (logic 0), the

DS1876 sets the DACs with the value associated with

the present temperature. When asserted, soft TXD1 or

soft TXD2 (TXDC) (Lower Memory, Register 6Eh) would

allow a software control identical to the TXD1 or TXD2 pin

(Figure 2). The POLARITY register (Table 02h, Register

C6h) determines if the off-state value of the DACs is

VREFIN or 0V.

Quick-Trip Timing

As shown in Figure 3, the DS1876’s input compara-

tor is shared among the six quick-trip alarms (TXP1

HI, TXP1 LO, TXP2 HI, TXP2 LO, BIAS1 HI, and BIAS2

HI). The comparator polls the alarms in a multiplexed

sequence. The updates are used to compare the HTXP1,

LTXP1, HTXP2, and LTXP2 (monitor diode voltages) and

the HBATH1 and HBATH2 (BMON1, BMON2) signals

against the internal APC and BIAS reference, respec-

tively. Depending on the results of the comparison, the

Table 1. Acronyms

Figure 1. Power-Up Timing

Figure 2. TXD1, TXD2 Timing

VCC

VPOA

DAC

SETTINGS

HIGH IMPEDANCE

OFF STATE

LUT VALUE

500µs

tINIT

tOFF

tON

TXD_

DAC

SETTINGS

LUT VALUE

OFF STATE

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

Tracking Error

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

TOSA

Transmit Optical Subassembly

TXP

Transmit Power

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