DESCRIPTION
s
DC bias current adjustable to 25mA
s
Buffered Loss-of-Signal output when used with
SY88903
s
Controlled laser diode turn on
s
Laser diode over-current detect
s
Monitor diode power control circuit
s
Laser diode driver enable
s
Designed for use with SY88902 and SY88903
s
Single power supply
s
Available in 16-pin MSOP
The SY88904 is an integrated controller for the SY88902
Laser Driver and SY88903 Laser Receiver that provides
power control and system interface functions for a complete
module solution. The SY88904 is designed to provide the
laser diode with an independent DC threshold current (I
BIAS
)
source to assure optimum laser diode performance. It has
special safety features which disable the currents to the
laser diode if certain faults are detected in the module. The
SY88904 also provides buffered Loss-of-Signal (LOS) output
in open collector level. The device is designed for fast and
accurate calibration of the laser diode as well as deriving
the control signals for system integration.
The SY88904 provides for delayed turn on of the laser
diode on system start up, chatter-free Loss-of-Signal, Low
V
CC
detect and laser diode over-current situations. Once
the optimal operating point is determined and set for a
specific laser diode, the threshold current (I
BIAS
) is designed
to automatically compensate for laser diode aging and
module temperature.
FEATURES
FIBER OPTIC MODULE
CONTROLLER WITH APC
SY88904
FINAL
APPLICATIONS
s
Controller for High Speed Optical Data Transmission
s
1.25Gbps Gigabit Ethernet
s
531 Mbps and 1062Mbps Fibre Channel
s
622Mbps SONET
s
Gigabit Interface Converter
PIN CONFIGURATION
BLOCK DIAGRAM
16
1
15
2
13
4
11
6
8
10
7
12
5
14
3
MSOP
K16-1
9
TX_Out
V
REF
I
BIAS
I
LIMIT SET
I
BIAS SET
I
BIAS FB
MD
I
PIN SET
V
CC
LOS
OUT
R
WIN
TX_Disable
TX_Fault
V
CC
DET
GND
LOS
IN
Fault
Detect
Circuit
TX_Out
TX_Fault
TX_Disable
I
PIN
SET
LOS
OUT
GND
V
REF 4
I
I_LIMIT
MD_Low
V
REF 3
V
REF 2
V
CC
V
REF
I
BIAS FB
I
BIAS
SET
40X
LOS
IN
-
+
-
+
-
+
I
LIMIT SET
I
BIAS
MD
V
CC
DET
4.75
R
WIN
V
CC
DET
TTL
PECL
PECL
OC
TTL
1
Rev.: A
Amendment: /1
Issue Date:
July 2000
2
SY88904
FINAL
Micrel
T
A
= 0
C
T
A
= +25
C
T
A
= +85
C
Symbol
Parameter
Min.
Typ.
Max.
Min.
Typ.
Max.
Min.
Typ.
Max.
Unit
Conditions
I
CC
Power Supply Current
--
--
60
--
--
60
--
--
60
mA
No output load
I
BIAS
I
BIAS
Output Current
2
--
25
2
--
25
2
--
25
mA
I
BIAS
SET
I
BIAS
SET
Input Current
--
--
0.625
--
--
0.625
--
--
0.625
mA
PIN DEFINITIONS
Pin
Type
Description
V
CC
Power Supply
Positive Power supply
GND
Ground
Ground
TX_Out
PECL Output
Transmitter Enable
TX_Fault
Open Collector Output
Module Fault
TX_Disable
TTL Input
Transmitter Disable and Fault Reset
LOS
IN
TTL Input
Loss-of-Signal Input from Limiting Post Amplifier
V
REF
Analog Output
Reference Voltage
I
PIN SET
Analog Input
Adjustable, Resistor to V
REF
sets Min. Monitor Diode Photo Current
R
WIN
Analog Input
Restart Window
LOS
OUT
PECL Output
Loss-of-Signal PECL output
I
BIASFB
Analog Output
Monitor Diode Feedback
I
BIASSET
Analog Input
Adjustable, Resistor to V
REF
sets the DC bias current for the Laser Diode
MD
Analog Input
Monitor Diode Connection
I
BIAS
Analog Input
DC bias current for the Laser Diode
I
LIMIT SET
Analog Input
Adjustable, Resistor to V
REF
sets Laser Diode over current fail point.
DC ELECTRICAL CHARACTERISTICS
V
CC
= +5V, R
LOAD
= 50
to 3V, T
A
= 0
C to +85
C
Symbol
Rating
Value
Unit
V
CC
Power Supply Voltage
0 to +7.0
V
TX_Disable, LOS
Input Voltage
0 to V
CC
V
LOS
OC,
I
PIN SET,
I
LIMIT SET
Others; I/O Voltage
0.3V, V
CC
+0.3V
V
I
BIASFB,
I
BIAS SET
TX_Out
Output Voltage (with 50
load)
V
CC
2.5V, V
CC
+0.3V
V
T
A
Operating Temperature Range
0
C to +85
C
C
T
store
Storage Temperature Range
55
C to +125
C
C
Theta Junction to Ambient
93
C/W
ABSOLUTE MAXIMUM RATINGS
(1)
NOTE:
1. Permanent device damage may occur if ABSOLUTE MAXIMUM RATINGS are exceeded. This is a stress rating only and functional operation is not implied
at conditions other than those detailed in the operational sections of this data sheet. Exposure to ABSOLUTE MAXIMUM RATlNG conditions for extended
periods may affect device reliability.
3
SY88904
FINAL
Micrel
LOGIC DIAGRAM
DETAILED DESCRIPTION
The SY88904 is an integrated control circuit for laser
diode modules intended for high-frequency fiber-optic
applications. The device is designed to operate with the
SY88902 laser diode driver providing Automatic Power
Control (APC) which provides bias and modulation current
control, laser diode driver enable and monitor diode interface.
The device also interfaces with the SY88903 high-speed
limiting amplifier providing chatter-free Loss of Signal
function. The system functions provided include laser diode
over-current detection, module fault signal and transmit
disable control. The SY88904 also provides power up cycling
of laser diode current and the fault detect signal.
Laser Diode Supply Current
The SY88904 provides the adjustable drive current for
the laser diode, DC bias.
Laser Diode Over-Current Detection
The SY88904 provides the ability to set an upper limit
fail point for the laser diode. I
LIMIT SET
sets an upper limit
for the average current present at the I
BIAS
pin.
Monitor Diode
The MD pin on the SY88904 provides low frequency
light intensity, laser power out feedback from the monitor
diode in the laser diode package. This feedback is used to
adjust the I
BIAS
level through the Automatic Power Control
circuit to maintain a near constant power output from the
laser diode. The SY88904 will also generate a fault if the
MD pin receives photo current less than I
PINSET
or is no
longer connected to the monitor diode.
Laser Diode Driver Enable
The SY88904 provides a TX_Out pin used to control the
output of the laser diode driver, through the Enable pin , of
the SY88902. This is a single ended PECL output.
Module Fault
The SY88904 provides an open collector output,
TX_Fault, that indicates to the host system that the module
is in a fault condition. The SY88904 will assert TX_Fault
when a low V
CC
condition is detected, when the monitor
diode is not connected or when a laser diode over-current
condition is detected. The SY88904 will attempt to clear a
TX_Fault condition if the device is power cycled or a reset
cycle is initiated with TX_Disable. When the SY88904 is in
a TX_Fault condition Ibias will be removed, TX_Out will be
negated and fault detection will be disabled.
Power Up Sequence, TX_Disable asserted
The SY88904 will power up in a TX_Fault condition and
will remain in a fault condition while TX_Disable is asserted.
Power Up Sequence, TX_Disable negated
The SY88904 will power up in a TX_Fault condition and
will remain in a fault condition until V
CC
is within operational
limits, at which time an initialization sequence will be started.
TX_Disable Cycle, TX_Fault Negated
When the SY88904 is not in a TX_Fault condition, a
rising edge of TX_Disable will cause the SY88904 to enter
a TX_Fault condition. The falling edge of TX_Disable will
cause a power up sequence to be started.
TX_Disable Cycle, TX_Fault Asserted
When the SY88904 is in a TX_Fault condition, the falling
edge of TX_Disable will cause an initialization sequence to
be started.
TX_Disable Cycle, during an initialization cycle
A rising edge of TX_Disable will cause the SY88904 to
terminate the current initialization cycle and remain in a
TX_Fault condition. The falling edge of TX_Disable will cause
the initialization sequence to be restarted.
Initialization Sequence
The initialization sequence consists of a delay, set by
the RC time constant on the Rwin input, followed by a
power up sequence.
Power Up Sequence
A power up sequence will negate TX_Fault and then
ramp up Ibias, controlled by the capacitor on the Rwin input
and an internal 1mA current, followed by TX_OUT being
negated and fault checking. If a fault occurs at this time the
module will enter a TX_Fault conditions, otherwise the
module will be ready for operation.
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