MAX3863ETJ+ Maxim Integrated Products, MAX3863ETJ+ Datasheet - Page 9

• Manufacturer Part Number: MAX3863ETJ+
• Description: IC LASR DRVR 2.7GBPS 3.6V 32TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of MAX3863ETJ+

• Data Rate: 2.7Gbps
• Number Of Channels: 1
• Voltage - Supply: 3.15 V ~ 3.6 V
• Current - Supply: 58mA
• Current - Modulation: 80mA
• Current - Bias: 100mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 32-WFQFN Exposed Pad
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Table 1. Optical Power Relations
use information about the effects of temperature and
aging. The laser driver automatically adjusts the bias to
maintain the constant average power. The new bias con-
dition requires proper compensation of the modulation
current. The designer must predict the slope efficiency of
the laser after its bias threshold current has changed.
The modulation and bias currents under a single operat-
ing condition:
For AC-coupled diodes:
The required compensation factor is then:
Once the value of the compensation factor is known, the
fixed portion of the modulation current is calculated from:
To allow larger modulation current, the laser is AC-
coupled to the MAX3863. In this configuration, a con-
stant current is supplied from the inductor L
MOD pin is conducting, half of I
L
Average Power
Extinction Ratio
Optical Power of a 1
Optical Power of a Zero
Optical Amplitude
Laser Slope Efficiency
Modulation Current
Threshold Current
Bias Current
Laser to Monitor
Transfer
P
and half is from the laser diode. When MOD is off,
PARAMETER
I
K
MOD
I
=
MODS
I
_______________________________________________________________________________________
BIAS
=
I
I
MOD
BIAS
2
=
×
=
SYMBOL
2.7Gbps Laser Driver with Modulation
2
2
I
I
TH
MOD
ρ
P
I
I
P
P
MOD
BIAS
MON
−
−
I
AVG
P
P
r
TH
P-P
AVG
η
e
1
0
η
+
I
I
MOD
BIAS
I
−
MOD
K I
×
2
MOD
1
1
r
r
×
P
r
P
P
P
η = P
I
P
I
I
e
MOD
BIAS
MD
e
e
AVG
1
0
P-P
0
+
−
Current Limits
BIAS
= P
= 2P
= 2P
at I ≥ I
1
/P
1
is supplied from
= P
≥ I
P-P
= P
RELATION
AVG
1
= (P
/P
AVG
AVG
TH
/I
1
P-P
0
MOD
P
TH
- P
+ I
0
. When the
r
/(r
/η
e
+ P
/(r
e
0
MOD
+ 1)
e
1
+ 1)
)/2
/2
the current from the inductor flows to the bias input.
This reduces the current through the laser diode from
the average of I
peak-to-peak current through the laser diode is then
I
ment for compliance in the AC-coupled circuit:
• V
• R
• L—Diode lead inductance (1nH typ)
• R
The time constant associated with the output pullup
inductor and the AC-coupling capacitor, impacts the
pattern-dependent jitter. For this second-order network
L
C
Keep the peak voltage droop less than 3% of the peak-
to-peak amplitude during the maximum CID period t.
The required time constant:
If τ = L
Place a good high-frequency inductor of 2µH on the
transmission line to the laser. Then you can place a
low-frequency inductor of 33µH at a convenient dis-
tance from the driver output.
When the APC loop is enabled, the actual bias current is
reduced from the maximum value to maintain constant
current from the monitor diode. With closed-loop control,
the bias current will be set by the transfer function of the
monitor diode to laser diode current. For example, if the
transfer function to the monitor diode is 10.0µA/mA, then
setting I
The bias current must be limited in case the APC loop
becomes open. The bias current also needs a set point
in case the APC control is not used. The BIASMAX pin
sets the maximum bias current. The BIASMAX current is
established by an internal current regulator, which main-
tains the bandgap voltage of 1.2V across the external
MOD
P
D
usually limits the low-frequency cutoff. The capacitor
is selected so:
D
L
D
. See the Typical Operating Circuit . The require-
—Diode bias point resistance (5Ω typ)
—Diode bias point voltage (1.2V typ)
—Series matching resistor (20Ω typ)
P
MD
/25Ω, and t = 100UI = 40ns, then L
for 500µA results in I
V
C
CC
D
Programming the Bias Current
BIAS
×
−
(
Compensation
R
I
2 8
τ
MOD
D
. % =
=
by half of I
2
+
35
R
L
×
×
)
1
(
t
>
R
−
D
(
e
R
+
−
D
τ
BIAS
t
L
MOD
R
+
P
L
R
)
L
≥
equal to 50mA.
. The resulting
)
1 8
.
V
P
= 35µH.
9