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FOA2251A1 FOA2252A1
2.5 Gb/s Laser Driver
Preliminary Data
Bipolar IC
Features
* Data rate up to 2.5 Gb/s * Supply range from + 3.0 V to + 5.0 V * Maximum power consumption typically 50 mA * Modulation current programmable up to 60 mA * DC offset programmable up to 60 mA * Temperature coefficient of the laser diode adjustable * Integrated bias control * Integrated laser supervisor for all vital laser functions
P-MQFP-44-2
Applications
* Fiber optics data communication systems * SONET OC-48, SDH STM-16
Type FOA2251A1 FOA2252A1
Ordering Code Q67000-Hxxxx Q67000-Hxxxx
Package P-MQFP-44-2 bare die
Semiconductor Group
1
August 98
FOA2251A1 FOA2252A1 GENERAL This document defines the ratings and characteristics of a laser driver circuit dedicated for applications within data communication modules with respect to various transmission standards and laser safety requirements. A block diagram of this circuit is shown in figure 1. The laser driver mainly consists of a modulator, a laser diode bias current controller and a laser- / V CC supervisor circuit. Modulator: The modulator is capable of driving modulation currents up to 60 mA. The modulation current is adjustable by an external resistor (RMOD). Furthermore there is a control input which defines the modulation current temperature dependency. The IC has an internal temperature compensation circuit for compensating the temperature characteristic of laser diode slope efficiency. With the external resistor (RTC), the modulation current temperature coefficient is adjustable. The temperature input itself derives from chip junction temperature. An input signal monitor circuit delivers an internal signal which is used for laser disabling, if data input is constantly high or low.
Bias Controller: The bias controller controls the laser diode's optical output power by adjusting the bias current. The controller cutoff frequency is adjustable by external capacitor (CBIAS). The laser bias current will start at < 300A after laser enable.
Laser Supervisor / VCC Supervisor: The laser supervisor circuit monitors the laser output power by the means of monitor diode feedback. The voltage generated by monitor diode circuit is compared to a reference. If the input voltage deviates more than 2dB (optical power 1dB) from this reference, the laser diode is switched off and a fault indication is generated. The VCC supervisor monitors the circuit power supply and switches off the laser if the VCC level is below the reset threshold. It is keeping the laser output down for the adjusted delay time (Power On Delay) after VCC has risen above the VCC reset threshold.
Semiconductor Group
2
August 98
FOA2251A1 FOA2252A1
BLOCK DIAGRAM
CFDEL LE LEN RSTN
VCCD
VCCA
CPDEL
VREF
MOD
VRef Laser Supervisor VCC Supervisor
Modulation Enable Bias Enable ISM Laser Enable
LDOFF
LF
DN D
O1 O2
Input Stage Input Signal Monitor
Modulator
O1N O2N VEE2 VEE2
MD
Bias Control
IBIAS
Bias Generator
VBIAS
VEE
CBIAS
CISM
TC
SBIAS
VEE1
Figure 1: General Circuit Block Diagram
Semiconductor Group
3
August 98
FOA2251A1 FOA2252A1
ABSOLUTE MAXIMUM RATINGS Stresses above the ones listed below may cause permanent damage to the device. Exposure to these values for extended periods may effect device reliability. If the device is operated beyond the range of operating conditions and characteristics, functionality cannot be guaranteed. All voltages given within this data sheet are referred to GND if not otherwise mentioned.
Rating
Supply Voltage Output Voltage at O, ON, BIAS, LDOFF, SBIAS Output Voltage at Logic Output LF Input Voltage at MD Input Voltage at Logic Inputs LE, LEN, RSTN Differential Data Input Voltage VD - VDN LDOFF Low Output Voltage Modulation Current at O,ON Bias Current at IBIAS Output Current Low at LF Junction Temperature Storage Temperature Relative Humidity (non-condensing) Electrostatic Discharge Voltage Capability Electrostatic Discharge Voltage Capability
Unit
V V V V V V V mA mA mA C C % kV kV
Min
-0.5 -0.5 -0.7 -0.5 -0.7
Max
5.5 VCC +0.7V VCC +0.7V 5.5 VCC +0.7V 2.5
Note
Note 1
VCC 1.2 80 80 3 -40 -55 125 150 95 2 1
D/DN and O/ON excluded D/DN Note 2
Notes:
1. A short-circuit at these outputs, either at logic high or low level, will not damage the device. 2. The input capacitance at these inputs will not exceed 0.6 pF.
Semiconductor Group
4
August 98
FOA2251A1 FOA2252A1
OPERATING CONDITIONS Under operating conditions defined below all specified characteristics will be met unless otherwise noted.
Condition
Environmental Junction Temperature Relative Humidity (non-condensing) Supply Voltage Range V 3 5.5 C % -40 125 95
Note1
Unit
Min
Max
Note
Notes:
1. Between -40C to -20C only the laser safety has to be guaranteed, all other parameters between -20C and +125C.
CHARACTERISTICS
SP
1
Characteristic
Laser Modulator Data Transmission Rate
Symbol
DR
Unit
GBd
Min
0
Typ.
Max
2.5
Note
into 10 Load Note 1 Note 2
2 3
Supply Current Modulation Current Range at Data Input High
for VccW3.7V and Tj=-40...125C or for VccW3.15V and TjW25C
ICC Imodhigh Imodlow
mA mA 0
50
75 60
4 5 6 7
Modulation Current at Data Input Low Modulation Current at Laser Shut Down O, ON Output Voltage Range Modulation Current Control Resistor Range (MOD-Resistor)
Imodlow ImodSD VO,VON RMOD
mA mA V k
0 0 1.5 0
2 2 4 4
Note 3, Offset Note 4
Note 5 Note19
Semiconductor Group
5
August 98
FOA2251A1 FOA2252A1
SP
8
Characteristic
Modulation Temperature Coefficient Resistor Range Serial Data Input
Symbol
RTC
Unit
k
Min
0.03
Typ.
Max
3
Note
Note 5,6
9 10 11 12 13 14 15
Data Input Voltage High Data Input Voltage Swing Data Input Current High Data Input Current Low VBB Output Voltage at D/DN Data Input Resistor Input Capacitance Logic Inputs RSTN, LE, LEN
VIH VD-VDN IIHD/DN IILD/DN VBB RIN CINPECL
V mV A A V k pF
2 200 - 300 VCC - 1.1 4 5
VCC -0.2 1000 300
VCC - 0.85 6 0.6
Note 7
Note 7
16 17 18 19 20 21 22
Input Voltage High Input Voltage Low Input Current High Input Current Low Logic Outputs LF Output Voltage Low Output Current High (Leakage Current) Output Current Low Input Signal Monitor (ISM)
VIHLOGIC VILLOGIC IIHLOGIC IILLOGIC VOLLOGIC IOHLOGIC IOLLOGIC
V V A A V A mA
2.0 0 -5
VCC 0.8 5
0.4 100 1
open collector sink current
23 24 25 26
ISM Delay Time vs. CISM Capacitor Range Duty Cycle for laser enable Duty Cycle for laser disable Duty Cycle for laser disable Laser Power Regulation / Control
tISMDEL CISM
s nF % % %
9 25 0 95 75 5 100
Note 8 Note 9
Input low Input high
27 28 29 30
max. Bias Current
for VccW3.15V and TjW50C
IBIASmax IBIASmin IBIASSD IBIAS ISBIAS
mA A A
60 300 300 110
Note 10
min. Bias Current Bias Current at Laser Shut Down Bias Current vs. Bias Monitor Current
Semiconductor Group
6
August 98
FOA2251A1 FOA2252A1
SP
31
Characteristic
Output Voltage Range BIAS, SBIAS Laser Supervising Circuit MD Failure Voltage High
Symbol VBIAS VSBIAS
Unit
V
Min
0.5
Typ.
Max
4
Note
VMD nom + 2.2dB
VMD nom + 2dB VMD nom - 2dB
32 MD Failure Voltage Low 33 MD Range without Failure Recognition Failure Recognition Time vs. CFDEL Capacitor Shut Off Time after Failure or Laser Disable RSTN Pulse Width vs. CFDEL VCC Reset Threshold for Laser Enable/Disable Power On Delay vs. CPDEL Capacitor Range LDOFF Low Output Current LDOFF High Output Current LDOFF High Output Voltage Reference Voltage 43 44 45 46 47 Voltage Range VREF VREF Source Current VREF Sink Current MD Reference Value VMDR Drift over Temperature Range VMDR Drift over Supply 48 Voltage Range 3 V ... 5.5 V VREF IREFsource IREFsink VMDR VMDR/ VMDR VMDR/ VMDR % V mA A V % tPDEL CPDEL tFDEL CFDEL tLDdis V
Note 11 optical: +1dB
VMD nom - 2.2dB VMD nom + 1.2dB
Note 11 optical: -1dB Note 12
VMD nom - 1.2dB
34
35 36 37 38 39 40 41 42
s nF s s nF V ms nF mA A V VCC -0.1 1.84
115
3 25 2.2 0.22 1 3 2 2.99
Note 9 Note 13 Note 18 Note 14
Note 15
Note 16 Note 9 sink current sink current
2.0
2.15 1 100 1.3 10
Note 17
1.1
10
Semiconductor Group
7
August 98
FOA2251A1 FOA2252A1 Notes:
1. The bias -, modulation-, the LF- and SBIAS output currents are not included. 2. This describes the AC modulation current (the DC component is the overall offset current). AC modulation current is drawn by O at VD > VDN, it is drawn by ON at VD < VDN. Imodhigh refers to drawn modulation current (AC + DC). Imodlow refers to an inactive current output (DC current only). 3. Inactive current output (see also note 2). 4. Modulation current when the laser diode is disabled. 5. Adjustment of programmable parameter by resistor value within this range. 6. Modulation current adaptation within junction temperature range. Low junction temperature represents a low additional modulation current. High junction temperature represents a high additional modulation current. 7. D/DN inputs are internally terminated to VBB by resistor RIN . See data input stage description. 8. If data input duty cycle falls below 5 % or exceeds 95 % the laser will be disabled after tISMDEL. On the other hand, the laser will be enabled within tISMDEL whenever the data input duty cycle goes back to 25 % ... 75 %. Data input duty cycle refers to the quotient given by number of ones divided by number of zeros within serial data stream. tISMDEL will be adjusted by external capacitor at CISM. 9. A capacitor within this range programs the time. 10. SBIAS is an open collector output for pulling up a resistor RSBIAS to monitor the bias current. 11. The supervisor circuit will detect a failure condition if MD voltage exceeds VMDnom 2dB range. VMDnom is given by nominal voltage level at MD which is set by VMDR. 12. The supervisor circuit will detect no failure condition if MD input voltage ranges from VMDnom -1.2dB to VMDnom + 1.2dB. VMDnom is given by nominal voltage level at MD which is set by VMDR. 13. A failure condition will be reported by LF if this condition lasts for tFDEL. This time can be adjusted by external capacitor at CFDEL. 14. Time between LF high (or LE low) and LDOFF high. 15. At supply voltages below VCC threshold the laser diode bias and modulation current will be held disabled and LDOFF will be held high. Above the laser diode will be enabled after the Power On Delay. 16. The Power On Delay is the reset time after V CC voltage has risen above the VCC reset threshold. During the Power On Delay the laser diode bias and modulation current will be held disabled and LDOFF will be held high. This time can be adjusted by external capacitor at CPDEL. 17. Temperature and voltage drift are included. 18. Minimal capacitor on CFDEL has to be chosen that the failure recognition time is longer than the settling time of the bias controller. 19. Adjusting the modulation current by RMOD notice that the increasing of RMOD will increase the modulation current. RMOD has to be adjusted that the modulation current is smaller than 60mA.
Semiconductor Group
8
August 98
FOA2251A1 FOA2252A1
TYPICAL CHARACTERISTIC OF TEMPERATURE COMPENSATION
Ratio of modulation currents for 100C and 0C (I 100C/I 0C) vs. RTC/Ohm
2,5
2 VCC=5V RMOD=600Ohm 1,5 VCC=5V RMOD=1400Ohm VCC=3.3V RMOD=600Ohm VCC=3.3V RMOD=1400Ohm
1
0,5
0 0 500 1000 1500 RTC / Ohm 2000 2500
Semiconductor Group
9
August 98
FOA2251A1 FOA2252A1
DATA INPUT STAGE Both data inputs D and DN are terminated to a VBB reference of nominal VCC - 1 V by resistors RIN. This easily provides the data input reference voltage at AC coupling. A schematic of the input stage is shown below:
D DN R R Reference Generator VBB
R = 5k
Figure 2: Data Input Stage
Semiconductor Group
10
August 98
FOA2251A1 FOA2252A1
LASER AND VCC SUPERVISING CIRCUIT If there is a fault signal (Laser Fault), this signal is stored and indicated by LF. The fault indication (LF) can be reset with low level at RSTN or with power down (VCC < VCC Reset Threshold) only. After power up, LF will always be cleared. Together with resetting LF, the external capacitor at CFDEL is charged to reset the fault delay time as well. This capacitor will also be charged whenever the laser is disabled by LE / LEN to accomplish equal fault delay times after laser enable, but this does not influence a previous fault indication by LF. The laser fault generation can be switched off by connecting CFDEL to VEE. The Power On Delay is the reset time after VCC voltage has risen above the VCC reset threshold. This time can be adjusted by an external capacitor at CPDEL. If CPDEL is shorted to VCC, there is no Power On Delay. The laser control by LE and LEN is fully redundant. This means only an 'AND' combination of LE = 1 / LEN = 0 can switch the laser on. The 'OR' combination of LE = 0 / LEN = 1 switches the laser off. To guarantee this on any single fault condition too, LE and LEN paths are implemented completely separate and redundant (see table 1 for clarification).
Semiconductor Group
11
August 98
FOA2251A1 FOA2252A1
LE
LEN
RSTN
in case of Laser Fault
VccLDOFF
Modulation Enable***
Bias Enable***
LF
0 X X X X 1
X 1 X X X 0
X X 1 0 X 1
0 0 1 X X 0
X X X X yes no**
1 1 1 1 1 0*
0 0 0 0 0 1
0 0 0 0 0 1
0 0 1 0 0 0
Table 1: Laser Diode Currents Enable / Disable Signals
* : sink current enabled = Low ** : after Power On Delay. *** : internal signal The table shows the static states of these signals. Dynamic changes or delays due to external delay capacitors are not shown. Bias current is disabled by setting Bias Enable low, modulation current is disabled by setting Modulation Enable low. LE and LEN do not effect LF. This means LF can not be reset by any combination of these signals.
INPUT SIGNAL MONITORING
Data Level in tISMDEL ISM Laser Enable*** LDOFF Modulation Enable*** Bias Enable*** LF
constant High constant Low
0 0
1 1
0 0
0 0
0 0
Table 2: Function of ISM Circuit
*** : internal signal
Semiconductor Group
12
August 98
FOA2251A1 FOA2252A1 INPUT / OUTPUT SIGNAL DESCRIPTION
Signal Name
D / DN
Function Differential Input
CFDEL
Control
CPDEL CISM IBIAS CBIAS SBIAS VBIAS
Control Control
Bias Output Control Monitor Output Bias Output
LDOFF
Laser Shut Down Output
LE LEN LF MD MOD O / ON RSTN TC VCCA VCCD VEE1 VEE2 VEE VREF
Logic Input Logic Input Logic Output Monitor Diode Input Control Differential Current Output Logic Input
Explanation Differential Data Input. D corresponds to O and DN to ON current output. With a high level at D and a low level at DN modulation current is drawn by O and ON is in high impedance state. With a low level at D and a high level at DN modulation current is drawn by ON and O is in high impedance state. Both inputs are prebiased to Vcc - 1 V, there input impedance is 5 k. With an external capacitor at CFDEL the laser fault detection delay time can be adjusted. This means if a constant fault condition is present, a laser fault indication will be generated and the laser will be shut down after this delay time. The laser fault (LF) generation can be switched off if CFDEL is connected to GND. With an external capacitor at CPDEL the Power On Delay time can be adjusted. There is no Power On Delay if CPDEL is shorted to VCC. With an external capacitor at CISM the delay time for detection of a low duty cycle input situation can be adjusted. If the input signal monitor is not used CISM has to be pulled down by 10 k resistor A sink current drawn by IBIAS determines the laser diode bias current. The controller characteristic can be set to an i-controller with an external capacitor at CBIAS and the time constants are selectable. SBIAS is an open collector output for pulling up a resistor to monitor the bias current with a fixed relation. This output can be connected to the base of an external bias current NPN transistor. It can be left open if not used. It is dedicated for applications which can not use the internal bias transistor because of too high circuit power dissipation. The output is not activated if VEE1 is connected to VEE. Whenever the laser diode is disabled LDOFF will deliver a high voltage level close to Vcc. This voltage is reduced by a minimum of 1.2 V if the laser diode is enabled. This output can be tied to the base of a pnp transistor to support a laser diode VCC shut down. If not used, this output can be left open without laser driver performance restrictions. A high level at LE enables, a low level disables the laser diode. For constant enable this input can be tied to VCC. A low level at LEN enables, a high level disables the laser diode. For constant enable this input can be tied to GND. Fault Indicator. A high level is generated whenever a fault situation is detected by the supervisor circuit. Fault situations are laser power failures indicated by MD input voltage deviation from VMDnom. This is the controller feedback input. The voltage at this input represents the monitor diode current and by this the laser output power. The bias current will be controlled to an equal level of MD and VMDR. An external resistor at MOD sets the modulation current level. These output signals drive the modulation current switched by D / DN data inputs and leveled by MOD, TC and chip junction temperature. Low active reset input. This input resets the LF indication if present. Further the laser diode is held within shut down mode if this signal is at low level. For constant laser diode enable this signal can be tied to VCC. An external resistor at TC sets the modulation current temperature coefficient. The temperature information is derived from chip junction temperature. Positive power supply for analog circuit part. Positive power supply for digital circuit part. Negative power supply, only connected to the output stage of bias generator, normally GND. Negative power supply, only connected to the output stage and the stage before of modulator, normally GND. Negative power supply of the rest of circuit, normally GND. VREF is a reference voltage output.
Control Power Supply Power Supply Power Supply Power Supply Power Supply Reference Voltage
Semiconductor Group
13
August 98
FOA2251A1 FOA2252A1
APPLICATION EXAMPLES
VCC VCC
100n VCCA SBIAS CFDEL
100n CPDEL
100n CBIAS LDOFF
*
D IN DN O1N/O2N IBIAS MD CISM TC MOD
FOA2251
O1/O2
LD
MD
1n
VCCA
VCCA
* if threshold current of laser is smaller than 2 mA
Figure 3: Positive Bias Regulation
VCC
LDOFF
IBIAS
FOA2251
O1/O2 O1N/O2N
LD MD
MD
Figure 4: Negative Bias Regulation
Semiconductor Group
14
August 98
FOA2251A1 FOA2252A1
PIN CONFIGURATION
bare die
LDOFF VEE2 VEE2 IBIAS O1N O2N O1 O2
LF CPDEL VCCD MOD TC VCCA
VBIAS VEE1
FOA2252
Size: 1,51 * 1,31 mm
2
SBIAS VEE CBIAS MD
RSTN
VREF
CISM
LEN
DN
LE
D
Figure 5: Pad assignment
P-MQFP-44-2
LDOFF VEE2 VEE2 IBIAS
O1N
O2N
NC
NC
CFDEL
NC
O1
NC NC LF CPDEL VCCD NC MOD TC VCCA NC NC
33
O2
22
NC NC VBIAS VEE1 SBIAS
FOA2251
NC VEE CBIAS MD
43 2 CFDEL 11
NC NC
RSTN
VREF
CISM
LEN
NC
DN
NC
Figure 6: Package pinning
Semiconductor Group
15
NC
LE
D
August 98
FOA2251A1 FOA2252A1
PACKAGE OUTLINE OF P-MQFP-44-2
Semiconductor Group
16
August 98

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