MAX3740AETG+ Maxim Integrated Products, MAX3740AETG+ Datasheet - Page 9

• Manufacturer Part Number: MAX3740AETG+
• Description: IC DRIVER SFP VCSEL 24-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Driverr

Specifications of MAX3740AETG+

• Data Rate: 3.2Gbps
• Number Of Channels: 1
• Voltage - Supply: 2.97 V ~ 3.63 V
• Current - Supply: 55mA
• Current - Modulation: 15mA
• Current - Bias: 15mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 24-TQFN Exposed Pad
• Mounting Type: Surface Mount
• Package: 24TQFN EP
• Maximum Data Rate: 3.2 Gbps
• Transmission Media Type: Optical Fiber
• Power Supply Type: Analog
• Typical Supply Current: 55 mA
• Maximum Operating Supply Voltage: 6 V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX3740A contains a bias generator with automat-
ic power control (APC), safety circuit, and a laser mod-
ulator with optional peaking compensation.
Figure 1 shows the bias generator circuitry that contains
a power-control amplifier and smooth-start circuitry. An
internal PNP transistor provides DC laser current to bias
the laser in a light-emitting state. The APC circuitry
adjusts the laser-bias current to maintain average power
over temperature and changing laser properties. The
smooth-start circuitry prevents current spikes to the laser
during power-up or enable, ensuring compliance with
safety requirements and extending the life of the laser.
The MD input is connected to the cathode of a monitor
diode, which is used to sense laser power. The BIAS
output is connected to the anode of the laser through an
inductor or ferrite bead. The power-control amplifier dri-
ves a current amplifier to control the laser’s bias current.
During a fault condition, the bias current is disabled.
The PWRMON output provides a voltage proportional to
average laser power given by:
Figure 1. Bias Generator
3.2Gbps SFP VCSEL Driver with Diagnostic
V
PWRMON
R
PWRSET
I
PD
_______________________________________________________________________________________
REF
MD
Detailed Description
= 2
SMOOTH-
✕
START
I
PD
C
COMP
1.8V
✕
R
PWRSET
Bias Generator
1.6V
(2V
2X
BE
)
AMPLIFIER
CONTROL
POWER-
PWRMON
COMP
MAX3740A
BIAS GENERATOR
1.2V
The BIASMON output provides a current proportional to
the laser bias current given by:
When APC is not used (no monitor diode, open-loop
configuration) connect the COMP and PWRMON pins
to GND. In this mode, the bias current is set by the
resistor R
used, connect a 1.7kΩ resistor between ground and
BIASSET to set the maximum bias current.
The safety circuit contains an input disable
(TX_DISABLE), a latched fault output (FAULT), and fault
detectors (Figure 2). This circuit monitors the operation
of the laser driver and forces a shutdown (disables
laser) if a fault is detected (Table 1). Table 2 contains
the circuit’s response to various single-point failures.
The transmit fault condition is latched until reset by a
toggle of TX_DISABLE or V
be pulled high with a 4.7kΩ to 10kΩ resistor.
Table 1. Fault Conditions
BIAS
BIASMON
PWRMON
PIN
I
BIAS
34
BIASSET
AMPLIFIER
CURRENT
BIASSET
200Ω
R
BIASSET
. When a closed-loop configuration is
I
BIASMON
V
V
V
I
BIAS
BIASMON
PWRMON
BIAS
ENABLE
9
> V
CC
= I
FAULT CONDITION
CC
> 0.8V
> 0.8V
BIASMON
BIAS
BIAS
- 0.2V
. The FAULT pin should
Monitors
R
BIASMON
/ 9
Safety Circuit
FERRITE
BEAD
9