LTC5100EUF#PBF Linear Technology, LTC5100EUF#PBF Datasheet - Page 28

• Manufacturer Part Number: LTC5100EUF#PBF
• Description: IC DRIVER VCSEL 3.2GBPS 16QFN
• Manufacturer: Linear Technology
• Type: Laser Diode Driverr

Specifications of LTC5100EUF#PBF

• Data Rate: 3.2Gbps
• Number Of Channels: 1
• Voltage - Supply: 3.135 V ~ 3.465 V
• Current - Supply: 54mA
• Current - Modulation: 12mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-QFN
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

OPERATIO
LTC5100
The EN pin and the Soft_en bit must both be active to
enable the transmitter, providing an extra degree of safety
and allowing full software control of the transmitter enable
function. As shown in Figure 6, the EN pin has a weak 10 A
current source that pulls it to the inactive state in case of
an accidental open on the pin. The EN and Soft_en bits are
inhibited until the LTC5100 has successfully loaded its
registers from an EEPROM or the Operating_mode bit has
been set, signaling that a microprocessor has assumed
control of the chip.
The first time the transmitter is enabled after initial power
up, the servo loops find the correct DAC settings for bias
and modulation current through a feedback process.
Initial settling is typically within 300ms. If the transmitter
is disabled and subsequently re-enabled, the previously
determined DAC settlings are restored. In this case set-
tling occurs typically within 1ms. This feature is called
“Rapid Restart” and can be overridden by setting the
Rapid
Table 1. Fault Detection and Handling
Fault Occurs When
Priority
Cleared by
Power-On Reset
Latched in the
FLT_STATUS
Register
Cleared from the
FLT_STATUS
Register on Read
Latched at the
FAULT Pin
Enabled by
Glitch Rejection
28
–
restart_en bit to zero.
U
LASER
OVERCURRENT
Laser Bias Current
Exceeds the Value
in the IB_LIMIT
Register
5
Yes
Yes
Yes
Yes
Over_current_en
4 s
LASER
OVERPOWER
Monitor Diode
Current is 50%
Greater Than the
Set Point
4
Yes
Yes
Yes
Yes
Over_pwr_en
and Apc_en
4 s
LASER
UNDERPOWER
Monitor Diode
Current is 50%
Less than the
Set Point
3
Yes
Yes
Yes
Yes
Under_pwr_en
and Apc_en
4 s
The LTC5100 has sophisticated eye safety and fault han-
dling features. Five types of faults are detected: low supply
voltage, excessive laser bias current, overpower,
underpower and EEPROM memory load failure. Table 1
summarizes these five faults and how they are handled in
the LTC5100.
Faults are latched in compliance with GBIC requirements.
Faults can be independently enabled (except for low sup-
ply voltage and memory load failure) and are recorded in
an internal register for readout over the serial bus. If two
faults occur simultaneously, the fault with the highest
priority (see Table 1) is recorded in the FLT_STATUS
register. This register indicates the cause of the fault and
is cleared only when read (not when the fault itself is
cleared.) Low supply voltage and memory load failure are
considered hard faults and cannot be masked or overrid-
den. They prevent the transmitter from begin enabled until
they are cleared.
Normally, a fault automatically disables the transmitter
and shuts down the laser. In some systems it may be
desirable to allow data transmission to continue after a
FAULT TYPE
EEPROM MEMORY
LOAD FAULT
EEPROM Load
Starts But Fails
to Complete
2
Yes
Yes
Yes
Yes
Always Enabled
NA
POWER SUPPLY
UNDERVOLTAGE
V
Below 2.8V
1
No
Yes
Yes
No (The FAULT Pin
Signals a Fault as
Long as the Supply Register)
Voltage Remains
Too Low)
Always Enabled
200mV Typical
Hysteresis
DD
Drops
FORCED FAULT
The Flt_pin_override
NA
No (Not Part of the
FLT_STATUS Register)
FLT_STATUS Register)
SOFTWARE
and Force_flt Bits
are Set
Yes
No (Not Part of the
Yes (Actually Latched
in the FLT_CONFIG
Flt_pin_override
NA
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