ADN2847ACPZ-32-RL Analog Devices Inc, ADN2847ACPZ-32-RL Datasheet - Page 10

• Manufacturer Part Number: ADN2847ACPZ-32-RL
• Description: IC,Laser Diode/LED Driver,LLCC,32PIN,PLASTIC
• Manufacturer: Analog Devices Inc
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of ADN2847ACPZ-32-RL

• Data Rate: 3.3Gbps
• Number Of Channels: 1
• Voltage - Supply: 3 V ~ 3.6 V
• Current - Supply: 50mA
• Current - Modulation: 80mA
• Current - Bias: 100mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 32-VFQFN, CSP Exposed Pad
• Mounting Type: Surface Mount
• Package: 32LFCSP EP
• Number Of Channels Per Chip: 1
• Operating Supply Voltage: 3 to 3.6 V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADN2847
The laser degrade alarm, DEGRADE, is provided to give a
warning of imminent laser failure if the laser diode degrades
further or environmental conditions continue to stress the LD,
such as increasing temperature.
The laser fail alarm, FAIL, is activated when the transmitter can
no longer be guaranteed to be SONET/SDH compliant. This
occurs when one of the following conditions arises:
•
•
DEGRADE is raised only when the bias current exceeds 90% of
ASET current.
MONITOR CURRENTS
IBMON, IMMON, IMPDMON, and IMPDMON2 are current
controlled current sources from V
modulation, and MPD current for increased monitoring
functionality. An external resistor to GND gives a voltage
proportional to the current monitored.
If the monitoring functions IMPDMON and IMPDMON2 are
not required, the IMPD pin and the IMPD2 pin must be
grounded and the monitor photodiode output must be
connected directly to the PSET pin.
DUAL MPD DWDM FUNCTION
(48-LEAD LFCSP ONLY)
The ADN2847 has circuitry for a second monitor photodiode,
MPD2. The second photodiode current is mirrored to
IMPDMON2 for wavelength control purposes and is summed
internally with the first monitor photodiode current for the
power control loop. For single MPD circuits, the MPD2 pin is
tied to GND.
This enables the system designer to use the two currents to
control the wavelength of the laser diode using various optical
filtering techniques inside the laser module.
If the monitor current functions IMPDMON and IMPDMON2
are not required, then the IMPD pin and IMPD2 pin can be
grounded and the monitor photodiode output can be connected
directly to PSET.
IDTONE (48-LEAD LFCSP ONLY)
The IDTONE pin is supplied for fiber identification/supervisory
channels or control purposes in WDM. This pin modulates the
optical one level over a possible range of 2% of minimum I
to 10% of maximum I
necting an external current sink between the IDTONE pin and
ground. There is a gain of two from this pin to the I
Figure 12 shows how the AD9850/AD9851 or the AD9834 can
be used with the ADN2847 to allow fiber identification.
The ASET threshold is reached.
The ALS pin is set high. This shuts off the modulation and
bias currents to the LD, resulting in the MPD current
dropping to zero. This gives closed-loop feedback to the
system that ALS has been enabled.
MOD
. The level of modulation is set by con-
CC
. They mirror the bias,
MOD
current.
MOD
Rev. A | Page 10 of 16
If the ID_TONE function is not used, the IDTONE pin should
be tied to V
can cause optical eye degradation.
DATA AND CLOCK INPUTS
Data and clock inputs are ac-coupled (10 nF capacitors are
recommended) and terminated via a 100 Ω internal resistor
between DATAP and DATAN, and also between the CLKP pin
and the CLKN pin. There is a high impedance circuit to set the
common-mode voltage that is designed to allow for maximum
input voltage headroom over temperature. It is necessary that ac
coupling is used to eliminate the need for matching between
common-mode voltages.
For input signals that exceed 500 mV p-p single-ended, it is
necessary to insert an attenuation circuit as shown in Figure 11.
CCBIAS
When the laser is used in ac-coupled mode, the CCBIAS pin
and the I
coupled mode, CCBIAS should be tied to V
I
To achieve optimum eye quality, one pull-up resistor (R
necessary, as shown in both circuits in Figure 14 and Figure 15.
The recommended resistor R
200 Ω ~ 500 Ω.
AUTOMATIC LASER SHUTDOWN
The ADN2847 ALS allows compliance to ITU-T-G958 (11/94),
section 9.7. When ALS is logic high, both bias and modulation
currents are turned off. Correct operation of ALS can be confirmed
if the FAIL alarm is raised when ALS is asserted. Note that this
is the only time DEGRADE is low while FAIL is high.
BIAS
BIAS
CC
pin should be tied together (Figure 15). In dc-
DATAN
DATAP
. Note that using IDTONE during transmission
NOTES
1. R
IMPEDANCE OF THE ADN2847.
R1
R2
Figure 10. AC Coupling of Data Inputs
IN
= 100Ω = THE DIFFERENTIAL INPUT
Figure 11. Attenuation Circuit
R3
DATAP/CLKP
DATAN/CLKN
50Ω
Z
ADN2847
50Ω
value is approximately
(TO FLIP-FLOPS)
V
REG
400µA TYP
R
R = 2.5kΩ, DATA
R = 3kΩ, CLK
ADN2847
R
IN
CC
.
Z
) is