ADN2871ACPZ-RL Analog Devices Inc, ADN2871ACPZ-RL Datasheet - Page 16

• Manufacturer Part Number: ADN2871ACPZ-RL
• Description: IC,Laser Diode/LED Driver,LLCC,24PIN,PLASTIC
• Manufacturer: Analog Devices Inc
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of ADN2871ACPZ-RL

• Data Rate: 4.25Gbps
• Number Of Channels: 1
• Voltage - Supply: 3 V ~ 3.6 V
• Current - Supply: 32mA
• Current - Modulation: 90mA
• Current - Bias: 100mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 24-VFQFN, CSP Exposed Pad
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADN2871
Resistor Setpoint
In resistor setpoint calibration, the current through the resistor
from PAVSET to ground is the I
method for measuring the I
resistor in series with the PAVSET resistor (or potentiometer)
and measure the voltage across this resistor, as shown in Figure 34.
The I
value of resistor used. In resistor setpoint calibration, PAVSET is
held to 1.2 V nominal; it is recommended that the sense resistor
be selected so that the voltage across the sense resistor does not
exceed 250 mV.
LOOP BANDWIDTH SELECTION
To ensure that the ADN2871 control loop has sufficient
bandwidth, the average power loop capacitor (PAVCAP) is
calculated using the laser’s slope efficiency (watts/amps) and
the average power required.
For resistor setpoint control:
For voltage setpoint control:
where:
P
LI is the typical slope efficiency at 25°C of a batch of lasers that
are used in a design (mW/mA).
LI can be calculated as
where:
P1 is the optical power at the one level (mW).
P0 is the optical power at the zero level (mW).
The capacitor value equation is used to get a centered value for
the particular type of laser that is used in a design and an average
power setting. The laser LI can vary by a factor of 7 between
different physical lasers of the same type and across temperatures
without the need to recalculate the PAVCAP value.
AV
is the average power required (mW).
MPD
PAVCAP
PAVCAP
LI
=
current is then equal to this voltage divided by the
P1
I
Sense Resistor in Resistor Setpoint I
MOD
Figure 34. Single Measurement of I
−
P0
=
=
PHOTODIODE
. 1
3
μ
2 .
28
C ADC
INPUT
×
×
10
10
− 6
− 6
V
MPD
×
×
CC
R
P
P
LI
LI
MPD
current is to place a small
AV
AV
PAVSET
current. The recommended
ADN2871
MPD
MPD
Monitoring
Across a
(mW/mA)
(Farad)
(Farad)
Rev. A | Page 16 of 20
This capacitor is placed between the PAVCAP pin and ground.
It is important that the capacitor is a low leakage, multilayer
ceramic type with an insulation resistance greater than 100 GΩ
or a time constant of 1000 seconds, whichever is less. Pick a
standard off-the-shelf capacitor value such that the actual
capacitance is within ±30% of the calculated value after the
capacitor’s own tolerance is taken into account.
POWER CONSUMPTION
The ADN2871 die temperature must be kept below 125°C. The
LFCSP has an exposed paddle, which should be connected so
that it is at the same potential as the ADN2871 ground pins.
Power consumption can be calculated as
Thus, the maximum combination of I
calculated, where:
I
with I
T
T
V
V
V
AUTOMATIC LASER SHUTDOWN (Tx_DISABLE)
ALS (Tx_DISABLE) is an input that is used to shut down the
transmitter’s optical output. The ALS pin is pulled up internally
with a 6 kΩ resistor and conforms to SFP MSA specifications.
When ALS is logic high or when open, both the bias and
modulation currents are turned off. If an alarm has triggered,
and the bias and modulation currents are turned off, ALS can
be brought high and then low to clear the alarm.
BIAS AND MODULATION MONITOR CURRENTS
IBMON and IMMON are current-controlled current sources
that mirror a ratio of the bias and modulation current. The
monitor bias current (IBMON) and the monitor modulation
current (IMMON) should both be connected to ground
through a resistor to provide a voltage proportional to the bias
current and modulation current, respectively. When using a
microcontroller, the voltage developed across these resistors can
be connected to two of the ADC channels, making available a
digital representation of the bias and modulation current.
CC
DIE
AMBIENT
BIAS_PIN
MODP_PIN
MODN_PIN
I
P = V
T
CC
min = 30 mA, the typical value of I
DIE
is the die temperature.
= I
BIAS
= T
CC
is the voltage at the IBIAS pin.
is the ambient temperature.
CC
= I
is the voltage at the IMODP pin.
is the voltage at the IMODN pin.
× I
AMBIENT
min + 0.3 I
MOD
CC
+ ( I
= 0.
+ θ
BIAS
JA
× V
MOD
× P
BIAS_PIN
) + I
MOD
BIAS
CC
( V
provided in Table 1
+ I
MODP_PIN
MOD
must be
+ V
MODN_PIN
)/2