MAX3669ETG+T Maxim Integrated Products, MAX3669ETG+T Datasheet - Page 9

• Manufacturer Part Number: MAX3669ETG+T
• Description: IC LASR DRVR 622MBPS 5.5V 24TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of MAX3669ETG+T

• Data Rate: 622Mbps
• Number Of Channels: 1
• Voltage - Supply: 3.14 V ~ 5.5 V
• Current - Supply: 40mA
• Current - Modulation: 75mA
• Current - Bias: 80mA
• 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

Resistor graph in the Typical Operating Character-
istics and select the value of R
sponds to the required current at +25°C.
When using the MAX3669 in closed-loop operation, the
R
able to the laser diode over temperature and life. The
APC loop can subtract from this maximum value but
cannot add to it. See the Bias Current vs. Maximum
Bias Set Resistor graph in the Typical Operating
Characteristics and select the value of R
corresponds to the end-of-life bias current at +85°C.
When the MAX3669’s APC feature is used, program the
average optical power by adjusting the APCSET resis-
tor. To select this resistor, determine the desired moni-
tor current to be maintained over temperature and life.
See the Monitor Diode Current vs. APC Set Resistor
graph in the Typical Operating Characteristics and
select the value of R
required current.
To minimize optical output aberrations due to the laser
parasitic inductance, an RC shunt network may be
used (see Typical Operating Circuit). If R
the laser diode resistance, the recommended total
resistance for R
al lasers are R
C
the output waveform. A bypass capacitor should also
be placed as close to the laser anode as possible for
best performance.
When transmitting NRZ data with long strings of consec-
utive identical digits (CIDs), LF droop can contribute to
PDJ. To minimize this PDJ, two external components
must be properly chosen: capacitor C
nates the APC loop time constant, and AC-coupling
capacitor C
To filter out noise effects and guarantee loop stability,
the recommended value for C
in an APC loop bandwidth of 20kHz. Consequently, the
PDJ associated with an APC loop time constant can be
ignored.
The time constant associated with the DC blocking
capacitor on I
important that this time constant produce minimum
droop for long consecutive bit streams.
BIASMAX
FILT
should be experimentally adjusted to optimize
Laser Driver with Current Monitors and APC
resistor sets the maximum bias current avail-
D
.
Interfacing with the Laser Diode
FILT
MOD
Pattern-Dependent Jitter (PDJ)
D
+ R
_______________________________________________________________________________________
= 20Ω and C
Programming the APC Loop
will have an effect on PDJ. It is
L
APCSET
is 10Ω. Starting values for coaxi-
APC
that corresponds to the
FILT
BIASMAX
is 0.1µF. This results
= 5pF. R
APC
, which domi-
BIASMAX
L
that corre-
represents
FILT
+3.3V, 622Mbps SDH/SONET
that
and
Referring to Figure 4, the droop resulting from long time
periods without transitions can be represented by the
following equation:
AC-coupling of I
that is equal to P
P
ensure a droop of less than 12% (6% relative to P
this equation can be solved for τ as follows:
If t
sition, the time constant associated with the DC block-
ing capacitor needs to be longer than:
R
estimated value of R
Assuming R
with C
The MAX3669 data inputs are PECL compatible.
However, it is not necessary to drive the MAX3669 with
a standard PECL signal. As long as the specified com-
mon-mode voltage and differential voltage swings are
met, the MAX3669 will operate properly.
Figure 4. Droop
p-p
FILT
1
P
p-p
τ
equals 80 consecutive unit intervals without a tran-
AC
equates to a 12% droop relative to P
D
can be ignored for C
= 1µF, τ
P
≥ R
AVG
AC
D
R
= 5Ω, and r
C
AC
Input Termination Requirement
(100% - DROOP) = e
τ =
D
AC
MOD
AVG
= 7.8 (80 bits) (1.6ns/bit) = 1.0µs
= 20Ω ⏐ ⏐ (R
= 6.7µs.
ln
AC
. An overall droop of 6% relative to
(1 - 0.12)
R
results in a discharge level for τ
τ << τ
AC
is:
-t
LASER
= 6.7Ω
AC
FILT
τ = ∞
t
D
1
= 5Ω:
= 7.8t
+ r
<< C
τ
LASER
AC
-t
τ
D
; therefore, the
)
DROOP
AVG
t
p-p
. To
),
9