DS1873T+ Maxim Integrated Products, DS1873T+ Datasheet - Page 12

• Manufacturer Part Number: DS1873T+
• Description: IC CTLR SFP+ ANLG LDD 28-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Controllerr

Specifications of DS1873T+

• 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
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 90-1873T+000

The DS1873 integrates the control and monitoring func-
tionality required to implement an SFP or SFP+ system.
Key components of the DS1873 are shown in the Block
Diagram and described in subsequent sections.
The DS1873 controls its laser bias current using its
BIAS DAC and the APC loop. The APC loop’s feedback
to the DS1873 is the monitor diode (MON2) current,
which is converted to a voltage using an external resis-
tor. The feedback is sampled by a comparator and
SFP+ Controller with Analog LDD Interface
12
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R
BD
Detailed Description
TOSA
BIAS DAC/APC Control
100Ω
+3.3V
R
MON
ROSA
LOS
BIAS MON
MON1
MON2
MON3
MOD
BIAS
DAC
DAC
compared to a digital set-point value. The output of the
comparator has three states: up, down, or no-opera-
tion. 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 incrementing and
decrementing the BIAS DAC setting.
The DS1873 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.
DS1873
LDD
EEPROM
QUICK
TRIP
ADC
LOS
I
DISABLE
2
TXDOUT
LOSOUT
C
Typical Operating Circuit
SDA
TXD
SCL
LOS
TXF
TX_FAULT
TX_DISABLE
MODE_DEF2 (SDA)
MODE_DEF1 (SCL)
LOS