ADN2873ACPZ-RL7 AD [Analog Devices], ADN2873ACPZ-RL7 Datasheet - Page 18

• Manufacturer Part Number: ADN2873ACPZ-RL7
• Description: 3.3 V, 50 Mbps to 4.25 Gbps, Single-Loop, Laser Diode Driver
• Manufacturer: AD [Analog Devices]

ADN2873
ALARMS
The ADN2873 has a latched, active high monitoring alarm
(FAIL). The FAIL alarm output is open drain in conformance
with SFP MSA specification requirements.
The ADN2873 has a three-fold alarm system that covers
•
•
•
The bias current alarm trip point is set by selecting the value
of resistor on the IBMON pin to GND. The alarm is triggered
when the voltage on the IBMON pin goes above 1.2 V. FAIL is
Table 5. ADN2873 Single-Point Alarms
Alarm Type
Bias Current
MPD Current
Crucial
Nodes
Table 6. ADN2873 Response to Various Single-Point Faults in AC-Coupled Configuration (as shown in Figure 35 and Figure 36)
Pin
PAVSET
PAVREF
RPAV
PAVCAP
DATAP
DATAN
ALS
ERSET
IMMON
ERREF
IBMON
FAIL
IMODP
IMODN
IBIAS
Use of a bias current that is higher than expected, likely as
a result of laser aging
Out-of-bounds average voltage at the monitor photodiode
(MPD) input, indicating an excessive amount of laser
power or a broken loop
Undervoltage in the IBIAS node (laser diode cathode) that
would increase the laser power
Fault state occurs
Voltage mode: fault state occurs
Fault state occurs
Short to V
Fault state occurs
Voltage mode: fault state occurs
Resistor mode: tied to V
Voltage mode: fault state occurs
Resistor mode: tied to V
Does not increase laser average power
Does not increase laser average power
Output currents shut off
Does not increase laser average power
Does not affect laser power
Resistor mode: tied to V
Fault state occurs
Does not increase laser average power
Does not increase laser average power
Fault state occurs
Mnemonic
IBMON
PAVSET
ERREF (the ERRREF designed is tied
to V
IBIAS
CC
CC
in resistor setting mode)
CC
CC
CC
Overvoltage or Short to V
Alarm if >1.2 V typical (±10% tolerance)
Alarm if >2.0 V
Alarm if shorted to V
valid for voltage setting mode only)
Ignore
Short to GND
Fault state occurs
Fault state occurs
Fault state occurs
Fault state occurs
Does not increase laser average power
Does not increase laser average power
Normal currents
Does not increase laser average power
Does not increase laser average power
Voltage mode: does not increase average
power
Resistor mode: fault state occurs
Does not increase laser average power
Does not increase laser average power
Does not increase laser average power
Does not increase laser average power
Fault state occurs
Rev. 0 | Page 18 of 20
CC
activated when the single-point alarms in Table 5 occur. The
circuit in Figure 37 can be used to indicate that FAIL has been
activated while allowing the bias and modulation currents to
remain on. The V
below 1.3 V, disabling the automatic shutdown of bias and modula-
tion currents. If an alarm has triggered and FAIL is activated,
ALS can be brought high and then low to clear the alarm.
(the alarm is
CC
Condition
ADN2873
BE
Figure 37. FAIL Indication Circuit
of the transistor clamps the FAIL voltage to
Undervoltage or Short to GND Condition
Ignore
Alarm if <0. 4V
Ignore
Alarm if shorted to GND
FAIL
Open
Fault state occurs
Fault state occurs
Circuit designed to tie to V
setting mode, so no open case
Voltage mode: fault state occurs
Resistor mode: does not increase
average power
Fault state occurs
Does not increase laser average power
Does not increase laser average power
Output currents shut off
Does not increase laser average power
Does not increase laser average power
Does not increase laser average power
Does not increase laser average power
Does not increase laser average power
Does not increase laser average power
Does not increase laser power
Fault state occurs
10kΩ
R1
V
CC
Q1
NPN
R2
330Ω
LED
D1
CC
in resistor