ADN2870 Analog Devices, Inc., ADN2870 Datasheet - Page 17

• Manufacturer Part Number: ADN2870
• Description: 3.3 V Dual-loop, 50 Mbps To 3.3 Gbps Laser Diode Driver
• Manufacturer: Analog Devices, Inc.

ALARMS
The ADN2870 has a latched active high monitoring alarm (FAIL).
The FAIL alarm output is an open drain in conformance to SFP
MSA specification requirements.
The ADN2870 has a 3-fold alarm system that covers
•
•
Table 5. ADN2870 Single-Point Alarms
Alarm Type
1. Bias Current
2. MPD Current
3. Crucial Nodes
Table 6. ADN2870 Response to Various Single-Point Faults in AC-Coupled Configuration as Shown in Figure 32
Pin
CCBIAS
PAVSET
PAVREF
RPAV
ERCAP
PAVCAP
DATAP
DATAN
ALS
ERSET
IMMON
ERREF
IBMON
FAIL
IMODP
IMODN
IBIAS
Use of a bias current higher than expected, probably as a
result of laser aging.
Out-of-bounds average voltage at the monitor photodiode
(MPD) input, indicating an indicating an excessive amount
of laser power or a broken loop.
Short to VCC
Fault state occurs
Fault state occurs
Voltage mode: Fault state occurs
Resistor mode: Tied to VCC
Voltage mode: Fault state occurs
Resistor mode: Tied to VCC
Does not increase laser 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 affect laser power
Voltage mode: Fault state occurs
Resistor mode: Tied to VCC
Fault state occurs
Fault state occurs
Does not increase laser average power
Does not increase laser average power
Fault state occurs
Pin Name
IBMON
PAVSET
ERREF
IBIAS
Over Voltage or Short to VCC Condition
Alarm if > 1.2 V
Alarm if > 1.7 V
Alarm if shorted to VCC
Ignore
Short to GND
Fault state occurs
Fault state occurs
Fault state occurs
Fault state occurs
Does not increase laser average power
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 17 of 20
•
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 activated when the single-point faults in Table 5 occur.
Undervoltage in IBIAS node (laser diode cathode) that
would increase the laser power.
Under Voltage or Short to GND Condition
Ignore
Alarm if < 0.9 V
Alarm if shorted to GND
Alarm if < 600 mV
Open
Does not increase laser average power
Fault state occurs
Fault state occurs
Voltage mode: Fault state occurs
Resistor mode: Does not increase
average power
Does not increase laser 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
ADN2870