VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7923
Features
• Rise Times Less Than 100ps
• High Speed Operation (Up to 2.4Gb/s NRZ Data)
• Single-Ended or Differential Input Operation
• Single Power Supply
• Direct Access to Modulation and Bias FETs
• Data Density Monitors
SONET/SDH 2.5Gb/s Laser Diode Driver
Applications
• SONET/SDH at 622Mb/s, 1.244Gb/s,
2.488Gb/s, 3.125Gb/s
• Full-Speed Fibre Channel (1.062Gb/s)
General Description
The VSC7923 is a single 5V supply, 2.4 Gb/s laser diode driver with direct access to the laser modulation and
bias FET’s. Laser bias and modulation currents are set by external components allowing precision monitoring
and setting of the current levels. Data inputs accept ECL levels. Data density outputs are provided to allow the
user to adjust the laser bias in high unbalanced data applications.
VSC7923 Block Diagram
IOUT
NIOUT
MK
NMK
DIN
VREF
IMOD
VIP
IBIAS
VIB
MIP
MIB
G52203-0, Rev 3.0
05/11/01
©
VITESSE
SEMICONDUCTOR CORPORATION
• 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com
Internet: www.vitesse.com
Page 1
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
SONET/SDH 2.5Gb/s Laser Diode Driver
Table 1: Signal Pin Reference
Signal
DIN
MK, NMK
NIOUT
IOUT
VSS
GND
VIP
MIP
VIB
MIB
VREF
Total Pins
VSC7923
Type
In
Out
Out
Out
Pwr
Pwr
In
In
In
In
In
Level
ECL
ECL
# Pins
1
2
1
1
Data Input
Description
Data Density Differential Outputs
Laser Modulation Current Output (Complementary)
Laser Modulation Current Output (To Laser Cathode))
Negative Voltage Rail
Positive Voltage Rail
Modulation Gate Node
Modulation Source Node
Bias Gate Node
Bias Source Node
Data Input Reference
Pwr
Pwr
DC
DC
DC
DC
DC
5
9
1
1
1
1
1
24
Table 2: Absolute Maximum Ratings
Symbol
V
SS
T
J
T
STG
Rating
Negative Power Supply Voltage
Maximum Junction Temperature
Storage Temperature
Limit
V
CC
to -6.0V
-55°C to + 125°C
-65°C to +150°C
Table 3: Recommended Operating Conditions
Symbol
GND
VSS
T
Cl
T
J
Parameter
Positive Voltage Rail
Negative Voltage Rail
Operational Temperature
Junction Temperature
(1)
Min
—
-5.5
-40
Typ
0
-5.2
Max
—
-4.9
85
(2)
Units
V
V
°C
°C
Conditions
—
—
—
Power dissipation = 1.25W
125
NOTES: (1) Lower limit of specification is ambient temperature and upper limit is case temperature. (2) See section “Calculation of the
Maximum Case Temperature” for detailed maximum temperature calculations.
Table 4: ECL Input and Outputs
Symbol
V
IN
V
OH
V
OL
Parameter
Input Voltage Swing
ECL Output High Voltage
ECL Output Low Voltage
Min
300
-1200
Typ
—
—
—
Max
800
Units
mV
mV
mV
Conditions
Peak-to-peak, V
REF
= -2.0V
50Ω to -2.0V
50Ω to -2.0V
—
-1600
—
Page 2
©
VITESSE
SEMICONDUCTOR CORPORATION
• 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com
Internet: www.vitesse.com
G52203-0, Rev 3.0
05/11/01
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7923
Table 5: Power Dissipation
Symbol
I
VSS
P
D
P
DMAX
SONET/SDH 2.5Gb/s Laser Diode Driver
Parameter
Power Supply Current (VSS)
Total Power Dissipation
Maximum Power Dissipation
Min
—
—
—
Typ
—
—
—
Max
220
1210
1815
Units
mA
mW
mW
Conditions
V
SS
= -5.5V, I
MOD
= I
BIAS
= 0mA
V
SS
= -5.5V, I
MOD
= I
BIAS
= 0mA,
R
LOAD
= 25Ω to GND
V
SS
= -5.5V, I
MOD
= 60mA,
I
BIAS
= 50mA, I
OUT
= 0V
Table 6: Laser Driver DC Electrical Specifications
Symbol
I
BIAS
I
MOD
V
IB
V
IP
V
OCM
Parameter
Programmable Laser Bias Current
Programmable Modulation Current
Laser Bias Control Voltage
Laser Modulation Control Voltage
Output Voltage Compliance
Min
2
2
—
—
GND -
2.2V
Typ
—
—
—
—
—
Max
50
60
V
SS
+
2.1
V
SS
+
2.1
—
Units
mA
mA
V
V
V
—
Conditions
—
I
BIAS
= 50mA
I
MOD
= 60mA
V
SS
= -5.2V
Table 7: Laser Driver AC Electrical Specifications
Symbol
t
R
, t
F
Parameter
Output Rise and Fall Times
Min
—
Typ
—
Max
100
Units
ps
Conditions
25Ω load, 20%-80%,
15mA < I
MOD
< 60mA,
I
BIAS
= 20mA
Table 8: Package Thermal Specifications
Symbol
θ
JCC
θ
JCMG
Parameter
Thermal Resistance from Junction-to-Case
Thermal Resistance from Junction-to-Case
Min
—
—
Typ
25
32
Max
—
—
Units
°C/W
°C/W
Conditions
Ceramic Package
Metal Glass Package
G52203-0, Rev 3.0
05/11/01
©
VITESSE
SEMICONDUCTOR CORPORATION
• 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com
Internet: www.vitesse.com
Page 3
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
SONET/SDH 2.5Gb/s Laser Diode Driver
VSC7923
Calculation of the Maximum Case Temperature
The VSC7923 is designed to operate with a maximum junction temperature of 125°C. The rise from the case to
junction is determined by the power dissipation of the device. The power dissipation is determined by the V
SS
current plus the operating I
MOD
and I
BIAS
currents.
The power of the chip is determined by the following formula:
P
D
=(-VSS * I
SS
) + ((V
IOUT
– V
SS
) * I
MOD
) + ((V
IBIAS
– V
SS
) * I
BIAS
)
For example with:
V
SS
I
MOD
I
BIAS
V
IBIAS
V
IOUT
=
=
=
=
=
-5.2V
40mA
20mA
-2.0V
-2.0V
P
D
= 5.2 * 220mA) + ((5.2 - 2.0) * 40mA) + ((5.2-- 2.0) * 20mA)
PD = 1144mW + 128mW + 64mW = 1.336W
The thermal rise from junction to case is
θ
JC
* P
D
. For the metal glass package,
θ
JC
= 32 °C/W. Thus the ther-
mal rise is:
32°C/W * 1.336W = 42.7°C
The maximum case temperature is:
125°C – 42.7°C = 82.3°C
The absolute maximum power dissipation of the device is at:
V
SS
I
MOD
I
BIAS
V
IBIAS
V
IOUT
P
D
P
D
=
=
=
=
=
-5.5V
60mA
50mA
0V
0V
= (5.5 * 220mA) + (5.5 * 60mA) + (5.5mA * 50mA)
=
1.815W
This will net a maximum junction to case thermal rise of: 1.815W * 32°C/W = 58°C
This situation will allow maximum case temperature of: 125°C – 58°C = 67°C
Page 4
©
VITESSE
SEMICONDUCTOR CORPORATION
• 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com
Internet: www.vitesse.com
G52203-0, Rev 3.0
05/11/01
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7923
Input Termination Schemes
SONET/SDH 2.5Gb/s Laser Diode Driver
Figure 1: Input Structure
OV (GND)
1400
DIN
X
VREF
X
4300
1400
+
-
4300
• Nominal VREF = -1.3V
• 1400, 4300 Ohm Resistor
on die, nominal values
-5.2V (VSS)
Figure 2: Single Ended AC Coupled
GND
0.1µF
SOURCE
GND
DIN
50 Ohms
GND
X
50Ω
VREF
+
X
0.1µF
GND
VSS
-
-2V
Figure 3: Differential AC Coupled
GND
0.1µF
SOURCE
0.1µF
DIN
X
GND
GND
+
50Ω
-2V
X
GND
GND
-
VSS
50Ω
-2V
VREF
G52203-0, Rev 3.0
05/11/01
©
VITESSE
SEMICONDUCTOR CORPORATION
• 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com
Internet: www.vitesse.com
Page 5
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