DS1878T+T&R Maxim Integrated Products, DS1878T+T&R Datasheet - Page 13

• Manufacturer Part Number: DS1878T+T&R
• Description: IC CTLR SFP W/DGTL LDD RX 28TQFN
• Manufacturer: Maxim Integrated Products
• Type: SFP+ Controllerr

Specifications of DS1878T+T&R

• Input Type: *
• Output Type: *
• Interface: *
• Current - Supply: *
• Mounting Type: Surface Mount
• Package / Case: 28-WFQFN exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Table 1. Acronyms
Figure 1. Modulation LUT Loading to a Maxim Laser Driver MOD DAC
ACRONYM
SFF-8472
VCSEL
ROSA
TOSA
SFP+
AGC
ADC
DAC
APC
APD
ATB
DFB
LDD
LOS
LUT
SEE
SFP
TXP
BM
TIA
SFF
NV
QT
TE
SFP+ Controller with Digital LDD Interface
8
7
6
5
4
3
2
1
0
Analog-to-Digital Converter
Automatic Gain Control
Automatic Power Control
Avalanche Photodiode
Alarm Trap Bytes
Burst Mode
Digital-to-Analog Converter
Distributed Feedback Laser
Laser Diode Driver
Loss of Signal
Lookup Table
Nonvolatile
Quick Trip
Tracking Error
Transimpedance Amplifier
Receiver Optical Subassembly
Shadowed EEPROM
Small Form Factor
Document Defining Register Map of SFPs
and SFFs
Small Form Factor Pluggable
Enhanced SFP
Transmit Optical Subassembly
Transmit Power
Vertical Cavity Self-Emitting Laser
-40
______________________________________________________________________________________
LOADED TO [7:0]
MODTC = 0
MOD LUT
DEFINITION
TEMPERATURE (°C)
MODTI
LOADED TO [8:1]
(DAC BIT 0 = 0)
MOD LUT
+102
A Maxim laser driver controls its laser bias current DAC
using the APC loop within the device. The APC loop’s
feedback to the device is the monitor diode (MON2)
current, which is converted to a voltage using an exter-
nal resistor. The feedback is sampled by a comparator
and compared to a digital set-point value. The output of
the comparator has three states: up, down, or no-oper-
ation. The no-operation state prevents the output from
excessive toggling once steady state is reached. As
long as the comparator output is in either the up or
down states, the bias is adjusted by writing increment
and decrement values to the Maxim laser driver
through the BIASINC register.
The device has an LUT to allow the APC set point to
change as a function of temperature to compensate for
tracking error (TE). The APC LUT has 36 entries that
determine the APC setting in 4°C windows between
-40°C and +100°C.
A Maxim laser driver controls the laser modulation
using the internal temperature-indexed LUT within the
device. The modulation LUT is programmed in 2°C
increments over the -40°C to +102°C range to provide
temperature compensation for the laser’s modulation.
The modulation is updated after each temperature con-
version using the 3-wire interface that connects to the
Maxim laser driver. A Maxim laser driver include a 9-bit
DAC. The modulation LUT is 8 bits.
Figure 1 demonstrates how the 8-bit LUT controls the
9-bit DAC with the use of a temperature control bit
BIAS Register/APC Control, 3-Wire Mode
8
7
6
5
4
3
2
1
0
-40
LOADED TO [8:1]
(DAC BIT 0 = 0)
MOD LUT
TEMPERATURE (°C)
MODTI
MODULATION Control
LOADED TO [7:0]
MODTC = 1
MOD LUT
+102
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