DS1874T+ Maxim Integrated Products, DS1874T+ Datasheet - Page 13

• Manufacturer Part Number: DS1874T+
• Description: IC CTLR SFP+ ANLG LDD 28-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Controllerr

Specifications of DS1874T+

• Number Of Channels: 1
• Voltage - Supply: 2.85 V ~ 3.9 V
• Current - Supply: 2.5mA
• Operating Temperature: -40°C ~ 95°C
• Package / Case: 28-WFQFN Exposed Pad
• Mounting Type: Surface Mount
• Number Of Outputs: 5
• Duty Cycle (max): 50 %
• Output Voltage: 0 V to 3.9 V
• Mounting Style: SMD/SMT
• Switching Frequency: 0 KHz to 400 KHz
• Operating Supply Voltage: 2.85 V to 3.9 V
• Supply Current: 2.5 mA to 10 mA
• Maximum Operating Temperature: + 95 C
• Fall Time: 300 ns
• Minimum Operating Temperature: - 40 C
• Rise Time: 300 ns
• Synchronous Pin: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 90-1874T+000

Table 1. Acronyms
Figure 1. Modulation LUT Loading to MAX3798/MAX3799 MOD DAC
ACRONYM
SFF-8472
ROSA
TOSA
SFP+
AGC
ADC
DAC
APC
APD
ATB
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
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
-40
______________________________________________________________________________________
LOADED TO [7:0]
MODTC = 0
MOD LUT
DEFINITION
TEMPERATURE (°C)
MODTI
LOADED TO [8:1]
(DAC BIT 0 = 0)
MOD LUT
+102
an external resistor. The feedback is sampled by a com-
parator and compared to a digital set-point value. The
output of the comparator has three states: up, down, or
no-operation. 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 MAX3798/MAX3799
through the BIASINC register (3-wire address 13h).
The DS1874 has an LUT to allow the APC set point to
change as a function of temperature to compensate for
tracking error (TE). The TE LUT has 36 entries that
determine the APC setting in 4°C windows between
-40°C to +100°C.
The MAX3798/MAX3799 control the laser modulation
using the internal temperature-indexed LUT within the
DS1874. 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
MAX3798/MAX3799. The MAX3798/MAX3799 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
(MODTC, Table 02h, Register C6h) and a temperature
index register (MODTI, Table 02h, Register C2h).
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
13