MAX3869EHJ+ Maxim Integrated Products, MAX3869EHJ+ Datasheet - Page 10

• Manufacturer Part Number: MAX3869EHJ+
• Description: IC LASER DRIVR 2CHAN 5.5V 32TQFP
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of MAX3869EHJ+

• Data Rate: 2.5Gbps
• Number Of Channels: 2
• Voltage - Supply: 3.14 V ~ 5.5 V
• Current - Supply: 64mA
• Current - Modulation: 60mA
• Current - Bias: 100mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 32-TFQFP, Exposed Pad
• Mounting Type: Surface Mount
• Operating Supply Voltage: 3.3 V
• Supply Current: 64 mA
• Maximum Power Dissipation: 1444 mW
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

should equal 25Ω. Typical values for R
23Ω. For best performance, a bypass capacitor (0.01µF
typical) should be placed as close as possible to the
anode of the laser diode. Depending on the exact char-
acteristics of the laser diode and PC board layout, a
resistor (R
tor L
in the optical output.
In some applications (depending on laser-diode para-
sitic inductance characteristics), an RC shunt network
between the laser cathode and ground will help mini-
mize optical output aberrations. Starting values for most
coaxial lasers are R = 75Ω in series with C = 3.3pF.
These values should be experimentally adjusted until
the optical output waveform is optimized.
When transmitting NRZ data with long strings of con-
secutive identical digits (CIDs), LF droop can occur
and contribute to pattern-dependent jitter (PDJ). To
minimize this PDJ, three external components must be
properly chosen: capacitor C
APC loop time constant; pull-up inductor L
coupling capacitor C
To filter out noise effects and guarantee loop stability,
the recommended value for C
in an APC loop bandwidth of 10kHz or a time constant
of 16µs. As a result, the PDJ associated with an APC
loop time constant can be ignored.
The time constant associated with the output pull-up
inductor (L
will also impact the PDJ. For such a second-order net-
work, the PDJ due to the low frequency cutoff will be
dominated by L
ommended value for C
mum CID period
voltage droop to less than 12% of the average (6% of
the amplitude). The time constant can be estimated by:
If
To reduce the physical size of this element (L
SMD ferrite beads is recommended (Figure 2).
The MAX3869 data and clock inputs are PECL compat-
ible. However, it is not necessary to drive the MAX3869
with a standard PECL signal. As long as the specified
common-mode voltage and the differential voltage
swings are met, the MAX3869 will operate properly.
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
10
τ
LP
P1
______________________________________________________________________________________
= L
can be useful in damping overshoot and ringing
P
P
/ 25Ω, and t = 100UI = 40ns, then L
P ≈
) of 20Ω to 70Ω in parallel with pull-up induc-
L
Input Termination Requirement
P2
P
. For a data rate of 2.5Gbps, the rec-
,
), and the AC-coupling capacitor (C
it is recommended to limit the peak
12% = 1 - e
D
.
τ
Pattern-Dependent Jitter
D
LP
is 0.056µF. During the maxi-
= 7.8t
APC
APC
-t
/
, which dominates the
τ
L P
is 0.1µF. This results
D
are 18Ω to
P
P
; and AC-
P
= 7.8µH.
), use of
D
)
The junction temperature of the MAX3869 dice must be
kept below +150°C at all times. The total power dissipa-
tion of the MAX3869 can be estimated by the following:
where I
MAX
cal laser forward voltage.
___________Applications Information
An example of how to set up the MAX3869 follows.
A communication-grade laser should be selected for
2.488Gbps applications. Assume the laser output aver-
age power is P
r
+85°C, and the laser diode has the following character-
istics:
The desired monitor diode current is estimated by
I
graph in the Typical Operating Characteristics shows
that R
To achieve a minimum extinction ratio (r
temperature and lifetime, calculate the required extinc-
tion ratio at +25°C. Assuming r
optical power P
required modulation current is 1.81(mW) / 0.05(mW/mA)
= 36.2mA. The I
Operating Characteristics shows that R
be 4.8kΩ.
MD
e
Wavelength:
Threshold Current:
Threshold Temperature
Coefficient:
Laser to Monitor Transfer:
Laser Slope Efficiency:
= 6.6 (8.2dB), the operating temperature is -40°C to
, I
= P
APCSET
MOD
Junction Temperature = P(W)
BIAS
AVG
P = V
is the modulation current, and V
is the maximum bias current set by R
·
should be 6.0kΩ.
Calculating Power Consumption
+ I
AVG
ρ
p-p
CC
MOD
MON
MOD
= 1.81mW, according to Table 1. The
✕
= 0dBm, minimum extinction ratio is
I
vs. R
= 200µA. The I
CC
(V
CC
+ (V
MODSET
- 25Ω
Determine R
CC
Determine R
e
λ = 1.3µm
Ι
β
ρ
η = 0.05mW/mA
at +25°C
= 20, the peak-to-peak
- V
TH
TH
MON
✕
graph in the Typical
f
I
= 22mA at +25°C
)
MOD
= 1.3%/°C
✕
✕
MD
45 (°C/W)
= 0.2A/W
Select Laser
I
MODSET
BIAS
e
/ 2)
vs. R
) of 6.6 over
f
is the typi-
MODSET
APCSET
APCSET
should
BIAS-