ADN2870ACPZ-RL7 Analog Devices Inc, ADN2870ACPZ-RL7 Datasheet - Page 15
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ADN2870ACPZ-RL7
Manufacturer Part Number
ADN2870ACPZ-RL7
Description
IC,Laser Diode/LED Driver,LLCC,24PIN,PLASTIC
Manufacturer
Analog Devices Inc
Type
Laser Diode Driver (Fiber Optic)r
Datasheet
1.ADN2870ACPZ.pdf
(20 pages)
Specifications of ADN2870ACPZ-RL7
Data Rate
3.3Gbps
Number Of Channels
1
Voltage - Supply
3 V ~ 3.6 V
Current - Supply
30mA
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
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Quantity
Price
LOOP BANDWIDTH SELECTION
To ensure that the ADN2870 control loops have sufficient
bandwidth, the average power loop capacitor (PAVCAP) and
the extinction ratio loop capacitor (ERCAP) are calculated
using the laser slope efficiency and the average power required.
For resistor setpoint control:
For voltage setpoint control:
where:
P
LI (mW/mA) is the typical slope efficiency at 25°C of a batch of
lasers that are used in a design.
The capacitor value equation is used to get a centered value for
the particular type of laser that is used in a design and average
power setting. The Laser LI can vary by a factor of 7 between
different physical lasers of the same type and across
temperature without the need to recalculate the PAVCAP and
ERCAP values. In the ac coupling configuration, LI can be
calculated as
where P1 is the optical power (mW) at the one level, and P0 is
the optical power (mW) at the zero level.
These capacitors are placed between the PAVCAP and ERCAP
pins and ground. It is important that these capacitors are low
leakage multilayer ceramics with an insulation resistance
greater than 100 GΩ or a time constant of 1000 sec, whichever
is less. The capacitor tolerance may be ±30% from the calculated
value to the available off-the-shelf value, including the tolerance
of the capacitors.
AV
(mW) is the average power required.
PAVCAP
ERCAP =
PAVCAP
ERCAP =
LI
=
P1
Sense Resistor in Resistor Setpoint I
I
Figure 31. Single Measurement of I
MOD
−
P0
=
=
PAVCAP
PAVCAP
. 1
3
PHOTODIODE
2 .
28
µC ADC
2
2
INPUT
×
×
10
10
−6
−6
×
×
V
P
CC
LI
P
AV
R
LI
AV
PAVSET
ADN2870
MPD
MPD
Monitoring
Across a
(mW/mA)
(Farad)
(Farad)
(Farad)
(Farad)
Rev. A | Page 15 of 20
POWER CONSUMPTION
The ADN2870 die temperature must be kept below 125°C. The
LFCSP package has an exposed paddle that should be connected
such that it is at the same potential as the ADN2870 ground pins.
Power consumption can be calculated as
I
P = V
T
Thus, the maximum combination of I
calculated.
where:
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 optical output. The ALS pin is pulled up internally
with a 6 kΩ resistor and conforms to SFP MSA specification.
When ALS is logic high or open, both the bias and modulation
currents are turned off.
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 micro-
controller, 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.
DATA INPUTS
Data inputs should be ac-coupled (10 nF capacitors are
recommended) and are terminated via a 100 Ω internal resistor
between the DATAP and DATAN pins. A high impedance
circuit sets the common-mode voltage and is designed to allow
maximum input voltage headroom over temperature. It is
necessary to use ac coupling to eliminate the need for matching
between common-mode voltages.
CC
CC
DIE
DIE
AMBIENT
BIAS_PIN
MODP_PIN
MODN_PIN
Specifications with I
= I
min is 30 mA, the typical value of I
= T
is the die temperature.
CC
CC
AMBIENT
× I
is the voltage at the IBIAS pin.
is the ambient temperature.
min + 0.3 I
is the voltage at the IMODP pin.
is the voltage at the IMODN pin.
CC
+ (I
+ θ
BIAS
JA
MOD
× P
× V
BIAS
BIAS_PIN
= I
MOD
) + I
= 0.
MOD
BIAS
CC
(V
provided in the
MODP_PIN
+ I
MOD
must be
+ V
ADN2870
MODN_PIN
)/2