MAX3795ETG Maxim Integrated Products, MAX3795ETG Datasheet - Page 12
MAX3795ETG
Manufacturer Part Number
MAX3795ETG
Description
Laser Driver 1Gbps to 4.25Gbps Mu ltirate VCSEL Driver
Manufacturer
Maxim Integrated Products
Type
Transmitterr
Datasheet
1.MAX3795ETG.pdf
(15 pages)
Specifications of MAX3795ETG
Operating Supply Voltage
3.3 V
Package / Case
TQFN-24 EP
Minimum Operating Temperature
- 40 C
Mounting Style
SMD/SMT
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
MAX3795ETG+T
Manufacturer:
MAXIM/美信
Quantity:
20 000
1Gbps to 4.25Gbps Multirate VCSEL Driver
with Diagnostic Monitors
current. For appropriate R
the Typical Operating Characteristics.
Select a communications-grade laser with a rise time of
90ps or better for 4.25Gbps applications. Use a high-
efficiency laser that requires low modulation current and
generates a low-voltage swing. Trim the leads to reduce
laser package inductance. The typical package leads
have inductance of 25nH per inch (1nH/mm). This
inductance causes a large voltage swing across the
laser. A compensation filter network can also be used to
reduce ringing, edge speed, and voltage swing.
A resistor (R
and ground controls the modulation current out of the
MAX3795 to the VCSEL. The modulation current is
given by the following:
It is important to note that the load impedance of the
VCSEL affects the modulation current being sourced by
the MAX3795. The Modulation Current vs. R
graph in the Typical Operating Characteristics shows the
current into a 50Ω load. Capacitance at the MODSET pin
should be ≤20pF.
The bias current output of the MAX3795 is controlled by
a resistor (R
and ground. In open-loop operation, BIASSET controls
the bias current level of the VCSEL. In closed-loop
operation (APC); the R
allowed bias current. The open-loop bias current is
given by the following:
The Bias Current vs. R
Operating Characteristics shows the current into a 50Ω
load. Capacitance at the BIASSET pin should be
≤20pF.
12
I
MOD
______________________________________________________________________________________
=
200
I
MODSET
BIASSET
BIAS
Programming Modulation Current
+
R
=
MODSET
1
) placed between the BIASSET pin
) placed between the MODSET pin
200
Programming Bias Current
BIASSET
+
BIASSET
R
TC
1 2
Design Procedure
×
BIASSET
.
and R
40
controls the maximum
graph in the Typical
×
MODSET
×
R
OUT
34
Select Laser
R
OUT
+
values, see
R
LOAD
MODSET
Compute the required modulation tempco from the
slope efficiency of the laser at T
higher temperature. Then select the value of R
the Typical Operating Characteristics. For example,
suppose a laser has a slope efficiency (SE) of
0.021mW/mA at +25°C, which reduces to 0.018mW/mA
at +85°C. The temperature coefficient is given by the
following:
From the Typical Operating Characteristics, the value
of R
modulation temperature compensation is not desired,
short TC1 and TC2.
Program the average optical power by adjusting
R
desired monitor current to be maintained over tempera-
ture and lifetime. See the Monitor Diode Current vs.
R
and select the value of R
required current.
Figure 4. Simplified Input Structure
Programming Modulation-Current Tempco
PWRSET
PWRSET
IN+
IN-
TC
PACKAGE
, which offsets the tempco of the laser, is 9kΩ. If
MAX3795
Laser tempco
1nH
1nH
graph in the Typical Operating Characteristics,
. To select the resistance, determine the
0.5pF
0.5pF
Programming the APC Loop
V
V
=
CC
CC
PWRSET
SE
=
(
SE
50Ω
50Ω
−
25
2380
85
×
1kΩ
−
(
ppm C
85 25
that corresponds to the
SE
A
−
25
V
= +25°C and at a
/
CC
°
)
)
×
15pF
10
6
TC
from