VITESSE
SEMICONDUCTOR CORPORATION
G52156-0, Rev 3.0
Page 1
05/01/01
VITESSE
SEMICONDUCTOR CORPORATION 741 Calle Plano Camarillo, CA 93012
Tel: (800) VITESSE FAX: (805) 987-5896 Email: prodinfo@vitesse.com
Internet: www.vitesse.com
Preliminary Data Sheet
VSC7924
SONET/SDH 2.5Gb/s Laser Diode Driver
Features
Applications
General Description
The VSC7924 is a single 5V supply, 2.5Gb/s laser diode driver with direct access to the laser modulation
and bias FETs. Laser bias and modulation currents are set by external components allowing precision monitor-
ing 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.
VSC7924 Block Diagram
Rise Times Less Than 100ps
High-Speed Operation
(Up to 2.5Gb/s NRZ Data)
Single-Ended Operation
Single Power Supply
Direct Access to Modulation and Bias FETs
Data Density Monitors
24-Pin Ceramic Package
SONET/SDH at 622Mb/s, 1.244Gb/s, and 2.488Gb/s
Full-Speed Fibre Channel (1.062Gb/s)
DIN
VREF
MK
NMK
IBIAS
NIOUT
IOUT
VIP
VIB
MIP
MIB
*Terminated to Off-chip Capacitor
IMOD
*TERM
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7924
SONET/SDH 2.5Gb/s Laser Diode Driver
Page 2
G52156-0, Rev 3.0
05/01/01
VITESSE
SEMICONDUCTOR CORPORATION 741 Calle Plano Camarillo, CA 93012
Tel: (800) VITESSE FAX: (805) 987-5896 Email: prodinfo@vitesse.com
Internet: www.vitesse.com
Table 1: Signal Pin Reference
Table 2: Absolute Maximum Ratings
Table 3: ECL Input and Outputs
Table 4: Recommended Operating Conditions
NOTES: (1) Lower limit of specification is ambient temperature and upper limit is case temperature.
(2) See "Calculation of the Maximum Case Temperature" section for detailed maximum temperature calculations.
Signal
Type
Level
# Pins
Description
DIN
In
ECL
1
Data Input
MK, NMK
Out
ECL
2
Data Density Differential Outputs
NIOUT
Out
1
Laser Modulation Current Output (Complementary)
IOUT
Out
1
Laser Modulation Current Output (To Laser Cathode))
VSS
Pwr
Pwr
5
Negative Voltage Rail
GND
Pwr
Pwr
8
Positive Voltage Rail
VIP
In
DC
1
Modulation Gate Node
MIP
In
DC
1
Modulation Source Node
VIB
In
DC
1
Bias Gate Node
MIB
In
DC
1
Bias Source Node
VREF
In
DC
1
Data Input Reference
TERM
In
DC
1
Data Input Reference
Total Pins
24
Symbol
Rating
Limit
V
SS
Negative Power Supply Voltage
V
CC
to -6.0V
T
J
Maximum Junction Temperature
-55C to + 125C
T
STG
Storage Temperature
-65C to +150C
Symbol
Parameter
Min
Typ
Max
Units
Conditions
V
IN
Input Voltage Swing
300
800
mV
Peak-to-peak, V
REF
= -1.3V
V
OH
ECL Output High Voltage
-1200
-700
mV
50
to -2.0V
V
OL
ECL Output Low Voltage
-2000
-1600
mV
50
to -2.0V
Symbol
Parameter
Min
Typ
Max
Units
Conditions
GND
Positive Voltage Rail
0
V
VSS
Negative Voltage Rail
-5.5
-5.2
-4.9
V
T
Cl
Operational Temperature
(1)
-40
85
(2)
C
Power dissipation = 1.25W
T
J
Junction Temperature
125
C
VITESSE
SEMICONDUCTOR CORPORATION
G52156-0, Rev 3.0
Page 3
05/01/01
VITESSE
SEMICONDUCTOR CORPORATION 741 Calle Plano Camarillo, CA 93012
Tel: (800) VITESSE FAX: (805) 987-5896 Email: prodinfo@vitesse.com
Internet: www.vitesse.com
Preliminary Data Sheet
VSC7924
SONET/SDH 2.5Gb/s Laser Diode Driver
Table 5: Power Dissipation
Table 6: Laser Driver DC Electrical Specifications
Table 7: Laser Driver AC Electrical Specifications
Table 8: Package Thermal Specifications
Symbol
Parameter
Min
Typ
Max
Units
Conditions
I
VSS
Power Supply Current (V
SS
)
220
mA
V
SS
= -5.5V, I
MOD
= I
BIAS
= 0mA
P
D
Total Power Dissipation
1120
mW
V
SS
= -5.5V, I
MOD
= I
BIAS
= 0mA,
R
LOAD
= 25
to GND
P
DMAX
Maximum Power Dissipation
1815
mW
V
SS
= -5.5V, I
MOD
= 60mA,
I
BIAS
= 50mA, I
OUT
= 0V
Symbol
Parameter
Min
Typ
Max
Units
Conditions
I
BIAS
Programmable Laser Bias Current
2
50
mA
I
MOD
Programmable Modulation Current
2
60
mA
V
IB
Laser Bias Control Voltage
V
SS
+
2.1
V
I
BIAS
= 50mA
V
IP
Laser Modulation Control Voltage
V
SS
+
2.1
V
I
MOD
= 60mA
V
OCM
Output Voltage Compliance
GND
-2.2V
V
V
SS
= -5.2V
Symbol
Parameter
Min
Typ
Max
Units
Conditions
t
R
, t
F
Output Rise and Fall Times
100
ps
25
load, 20%-80%,
15mA < I
MOD
< 60mA,
I
BIAS
= 20mA
Symbol
Parameter
Min
Typ
Max
Units
Conditions
JCC
Thermal Resistance from junction-to-case
25
C/W
Ceramic Package
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7924
SONET/SDH 2.5Gb/s Laser Diode Driver
Page 4
G52156-0, Rev 3.0
05/01/01
VITESSE
SEMICONDUCTOR CORPORATION 741 Calle Plano Camarillo, CA 93012
Tel: (800) VITESSE FAX: (805) 987-5896 Email: prodinfo@vitesse.com
Internet: www.vitesse.com
Calculation of the Maximum Case Temperature
The VSC7924 is designed to operate with a maximum junction temperature of 125C. 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
= (-V
SS
* I
SS
) + ((V
IOUT
V
SS
) * I
MOD
) + ((V
IBIAS
V
SS
) * I
BIAS
)
For example with:
V
SS
=
-5.2V
I
MOD
=
40mA
I
BIAS
=
20mA
V
IBIAS
=
-2.0V
V
IOUT
=
-2.0V
P
D
=
(-5.2 * 220mA) + ((5.2 - 2.0) * 40mA) + ((5.2
-
- 2.0) * 20mA)
P
D
=
1144mW + 128mW + 64mW = 1.336W
The thermal rise from junction to case is
JC
* P
D
. For the ceramic package,
JC
= 25C/W. Thus the ther-
mal rise is:
25C/W * 1.336W = 33.4C
The maximum case temperature is:
125C 33.4C = 91.6C
The absolute maximum power dissipation of the device is at:
V
SS
=
-5.5V
I
MOD
=
60mA
I
BIAS
=
50mA
V
IBIAS
=
0V
V
IOUT
=
0V
P
D
=
(5.5 * 220mA) + (5.5 * 60mA) + (5.5mA * 50mA)
P
D
= 1.815W
This will net a maximum junction to case thermal rise of: 1.815W * 25C/W = 45.4C
This situation will allow maximum case temperature of: 125C 45.4C = 79.6C
VITESSE
SEMICONDUCTOR CORPORATION
G52156-0, Rev 3.0
Page 5
05/01/01
VITESSE
SEMICONDUCTOR CORPORATION 741 Calle Plano Camarillo, CA 93012
Tel: (800) VITESSE FAX: (805) 987-5896 Email: prodinfo@vitesse.com
Internet: www.vitesse.com
Preliminary Data Sheet
VSC7924
SONET/SDH 2.5Gb/s Laser Diode Driver
Input Termination Schemes
Figure 1: Input Structure
Figure 2: Single-Ended AC Coupled
Figure 3: Single Ended AC Coupled with Offset Adjust
X
X
+
-
1400
1400
4300
GND
4300
OV (GND)
-5.2V (VSS)
DIN
VREF
X
TERM
Nominal VREF = -1.3V
1400, 4300 Ohm Resistor
on die, nominal values
12
p
F
3
1.4k
1.4k
4.3k
4.3k
Nominal V
REF
= 1.3V
1.4k
, 4.3k
resistor on die, nominal values
X
X
SOURCE
50
-2V
0.1
F
0.1
F
DIN
TERM or VREF
GND
VSS
+
-
GND
X
X
SOURCE
50
DIN
VREF
GND
GND
VSS
VSS
+
-
2000
4300
0.1
f
X
TERM
0.1
f
3
GND
2k
4.3k
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