MAX3656ETG+T Maxim Integrated Products, MAX3656ETG+T Datasheet - Page 10

• Manufacturer Part Number: MAX3656ETG+T
• Description: IC LASR DRVR 2.5GBPS 3.6V 24TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of MAX3656ETG+T

• Data Rate: 2.5Gbps
• Number Of Channels: 1
• Voltage - Supply: 3 V ~ 3.6 V
• Current - Supply: 40mA
• Current - Modulation: 85mA
• Current - Bias: 70mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 24-TQFN Exposed Pad
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: MAX3656ETG+T; MAX3656ETG+TTR

•
In each of the three cases listed, initialization is complete
within three bursts (bursts must comply with specified
burst on- and burst off-time) or the time specified in the
Electrical Characteristics table, whichever comes first.
The bias and modulation outputs (BIAS+ and OUT+)
can be switched on and off quickly using the differential
burst-enable inputs (BEN+ and BEN-). Once the APC
loop has initialized, the bias and modulation outputs are
switched on when BEN+ = high and BEN- = low and are
switched off when BEN+ = low and BEN- = high.
When BEN is switched on, the laser driver sinks the bias
and modulation currents set by the APCSET, BIASMAX,
and MODSET resistors within the maximum BEN delay
time of 2.3ns. For stable APC loop operation, the mini-
mum burst length is limited to the burst on-time listed in
the Electrical Characteristics table. The maximum burst-
on time is unlimited.
When BEN is switched off, the bias and modulation cur-
rents fall below the specified bias-off and modulation-
off currents within the maximum burst disable delay
time of 2.0ns. For stable APC loop operation, the mini-
mum burst off-time is limited to the value listed in the
Electrical Cha r acteristics table. The maximum burst off-
time is unlimited.
The MAX3656 provides short-circuit protection for the
modulation and bias-current sources. If BIASMAX or
MODSET is shorted to ground, the bias and modulation
outputs are turned off.
155Mbps to 2.5Gbps Burst-Mode
Laser Driver
10
APC loop reset), and then it is driven low (chip-
enabled). In this case, APC loop initialization begins
when the voltage at EN drops below the specified
EN input low voltage of 0.8V. After initialization
begins, the laser driver can be operating in burst
mode (BEN toggling high and low) or continuous
mode (BEN = high). In this case, the initialization
time is 2.1µs (typ).
Burst-Mode Startup
In burst-mode startup, the power-supply voltage is
within the specified limits and the chip is enabled
(EN = low). The burst-enable input is low (BEN =
low) and has not been in the high state since the
APC loop was reset. APC loop initialization begins
when the BEN input is driven high. After initialization
begins, the laser driver can be operating in burst
mode (BEN toggling high and low) or continuous
mode (BEN = high). In this case, the initialization
time is 1.6µs (typ).
______________________________________________________________________________________
Short-Circuit Protection
Burst-Mode Operation
When designing a laser transmitter, the optical output is
usually expressed in terms of average power and
extinction ratio. Table 1 shows the relationships helpful
in converting between the optical average power and
the modulation current. These relationships are valid if
the mark density and duty cycle of the optical wave-
form are 50%.
For a given laser power (P
and extinction ratio (r
calculated using Table 1. See the I
graph in the Typical Operating Characteristics , and
select the value of R
required current at +25°C.
When the MAX3656 is used in open-loop operation, the
R
select this resistor, determine the required bias current.
See the I
Operating Characteristics , and select the value of
R
open-loop operation, connect a 50kΩ resistor from
R
When using the MAX3656 in closed-loop operation, the
R
able to the laser diode over temperature and lifetime.
The APC loop can subtract from this maximum value,
but cannot add to it. See the I
graph in the Typical Operating Characteristics and
select the value of R
end-of-life bias current at +85°C. The R
should not be set less than 5kΩ.
Table 1. Optical Power Definition
Average power
Extinction ratio
Optical power high
Optical power low
Optical amplitude
Laser slope
efficiency
Modulation current
Laser-to-monitor
diode gain
BIASMAX
APCSET
BIASMAX
BIASMAX
PARAMETER
Programming the Modulation Current
to GND, and leave the MD pin open.
BIASMAX
that corresponds to the required current. For
resistor sets the maximum bias current avail-
resistor determines the bias current. To
Programming the Bias Current
SYMBOL
vs. R
A
P
I
P
MOD
e
BIASMAX
MODSET
AVG
P
P
LMD
r
P-P
η
), the modulation current can be
e
1
0
BIASMAX
Design Procedure
AVG
P
r
P
P
P
η = P
I
(2 x I
(r
MOD
e
AVG
1
0
P-P
e
= P
that corresponds to the
that corresponds to the
= 2P
= 2P
+ 1))
BIASMAX
), slope efficiency (η),
MD
= P
P-P
= P
1
= (P
graph in the Typical
/ P
AVG
AVG
1
/ I
/ I
P-P
MOD
RELATION
0
0
- P
MOD
MOD
+ P
/ (r
BIASMAX
× r
/ η
0
)((r
e
e
vs. R
1
vs. R
) / 2
/ (r
+ 1)
e
e
- 1) /
+ 1)
BIASMAX
MODSET
resistor