MAX3738ETG+ Maxim Integrated Products, MAX3738ETG+ Datasheet - Page 11

• Manufacturer Part Number: MAX3738ETG+
• Description: IC LASER DRIVER 4.25GBPS 24TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of MAX3738ETG+

• Data Rate: 4.25Gbps
• Number Of Channels: 1
• Voltage - Supply: 2.97 V ~ 3.63 V
• Current - Supply: 47mA
• Current - Modulation: 85mA
• Current - Bias: 100mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 24-TQFN Exposed Pad
• Mounting Type: Surface Mount
• Operating Supply Voltage: 3.3 V
• Supply Current: 47 mA
• Maximum Operating Temperature: + 85 C
• Maximum Power Dissipation: 1805 mW
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The safety circuitry contains a disable input
(TX_DISABLE), a latched fault output (TX_FAULT), and
fault detectors (Figure 5). This circuitry monitors the
operation of the laser driver and forces a shutdown if a
fault is detected (Table 1). The TX_FAULT pin should
be pulled high with a 4.7kΩ to 10kΩ resistor to V
required by the SFP MSA. A single-point fault can be a
short to V
response to various single-point failure. The transmit
fault condition is latched until reset by a toggle or
TX_DISABLE or V
laser diode shutdown through the optional shutdown
circuitry as shown in the Typical Application Circuit .
This shutdown transistor prevents a single-point fault at
the laser from creating an unsafe condition.
Table 2. Circuit Responses to Various Single-Point Faults
* A fault state asserts the TX_FAULT pin, disables the modulation and bias currents, and asserts the SHUTDOWN pin.
TX_DISABLE Modulation and bias currents are disabled.
SHUTDOWN
TX_FAULT
APCFILT1
APCFILT2
BC_MON
PC_MON
MODSET
APCSET
OUT+
OUT-
BIAS
PIN
IN+
MD
IN-
CC
155Mbps to 4.25Gbps SFF/SFP Laser Driver
or GND. See Table 2 to view the circuit
Does not affect laser power.
The optical average power increases, and a fault occurs
if V
responds by decreasing the bias current.
The optical average power decreases and the APC loop
responds by increasing the bias current. A fault state
occurs if V
This disables bias current. A fault state occurs.
Does not affect laser power. If the shutdown circuitry is
used, the laser current is disabled.
In this condition, the laser forward voltage is 0V and no
light is emitted.
The APC circuit responds by increasing the bias current
until a fault is detected; then a fault state* occurs.
Does not affect laser power.
Fault state* occurs.
Fault state* occurs.
I
voltage.
I
voltage.
Does not affect laser power.
Does not affect laser power.
BIAS
BIAS
PC_MON
CC
CIRCUIT RESPONSE TO OVERVOLTATGE OR
______________________________________________________________________________________
increases until V
increases until V
. The laser driver offers redundant
BC_MON
exceeds the threshold. The APC loop
exceeds the threshold voltage.
SHORT TO V
BC_MON
BC_MON
Safety Circuitry
exceeds the threshold
exceeds the threshold
CC
with Extinction Ratio Control
CC
as
The MAX3738 features monitors (BC_MON, PC_MON)
for bias current (I
monitors are realized by mirroring a fraction of the cur-
rents and developing voltages across external resistors
connected to ground. Voltages greater than V
PC_MON or BC_MON result in a fault state. For exam-
ple, connecting a 100Ω resistor to ground at each mon-
itor output gives the following relationships:
External sense resistors can be used for high-accuracy
measurement of bias and photodiode currents. On-chip
isolation resistors are included to reduce the number of
components needed to implement this function.
Does not affect laser power.
Normal condition for circuit operation.
The optical average power decreases, and the APC loop
responds by increasing the bias current. A fault state
occurs if V
The optical average power increases and a fault occurs
if V
responds by decreasing the bias current.
The APC circuit responds by increasing the bias current
until a fault is detected; then a fault* state occurs.
Does not affect laser power.
Fault state* occurs. If the shutdown circuitry is used, the
laser current is disabled.
Fault state* occurs. If the shutdown circuitry is used, the
laser current is disabled.
Does not affect laser power.
Does not affect laser power.
Does not affect laser power.
I
voltage.
I
voltage.
Fault state* occurs.
Fault state* occurs.
BIAS
BIAS
PC_MON
CIRCUIT RESPONSE TO UNDERVOLTAGE OR
increases until V
increases until V
V
Safety Circuitry Current Monitors
BC_MON
BC_MON
exceeds the threshold. The APC loop
V
PC_MON
BIAS
SHORT TO GROUND
exceeds the threshold voltage.
= (I
) and photocurrent (I
BC_MON
BC_MON
BIAS
= I
MD
/ 82) x 100Ω
exceeds the threshold
exceeds the threshold
x 100Ω
MD
REF
). The
11
at