VITESSE
SEMICONDUCTOR CORPORATION
G52157-0, Rev 3.2
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
VSC7925
SONET/SDH 2.5Gb/s Laser Diode Driver
Features
Applications
General Description
The VSC7925 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 density outputs are provided to allow the user to adjust the laser bias
in unbalanced data applications. Clock and data inputs have nominal 50
termination resistors and high fre-
quency decoupling capacitors.P
VSC7925 Block Diagram
Rise Times Less Than 100ps
High Speed Operation (Up to 2.5Gb/s NRZ Data)
Single-ended
Inputs
Single
Supply
Direct Access to Modulation and Bias FET's
Data Density Monitors
On-Chip Reclocking Register
24-Pin Ceramic Package
SONET/SDH at 622Mb/s, 1.244Gb/s, and
2.488Gb/s
Full-Speed Fibre Channel (1.062Gb/s)
DIN
NDIN*
10pF
50
MK
NMK
IBIAS
NIOUT
IOUT
MIP
VIP
VIB
MIB
D
Q
CLK
NCLK*
DCC
* Terminated to off-chip capacitor
10pF
50
**
**
**
**
** On-die components
I
MOD
I
BIAS
DCC
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7925
SONET/SDH 2.5Gb/s Laser Diode Driver
Page 2
G52157-0, Rev 3.2
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: High-Speed Inputs and ECL Outputs
Signal
Type
Level
# Pins
Description
DIN, NDIN
In
2
Data Input and Data Reference
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
4
Negative Voltage Rail
GND
Pwr
Pwr
6
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
IBIAS
Out
DC
1
Laser Bias Output (To Laser Cathode)
CLK, NCLK
In
2
Clock Input and Clock Reference
DCC
In
DC
1
Duty Cycle Control, Leave Floating
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
Single-ended Input Voltage Swing
300
1500
mV
V
CM
= -2.5V
V
CM
Differential Input Common Mode
Range
-3.3
-1.3
V
V
SS
= -5.2V
V
OH
ECL Output High Voltage
-1200
-500
mV
50
to -2.0V
V
OL
ECL Output Low Voltage
-2000
-1600
mV
50
to -2.0V
VITESSE
SEMICONDUCTOR CORPORATION
G52157-0, Rev 3.2
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
VSC7925
SONET/SDH 2.5Gb/s Laser Diode Driver
Table 4: Recommended Operating Conditions
NOTE: (1) Lower limit of specification is ambient temperature and upper limit is case temperature.
Table 5: Power Dissipation
Table 6: Laser Driver DC Electrical Specifications
Table 7: Laser Driver AC Electrical Specifications
Symbol
Parameter
Min
Typ
Max
Units
Conditions
GND
Positive Voltage Rail
0
V
V
SS
Negative Voltage Rail
-5.5
-5.2
-4.9
V
T
CASE KF
Operational Temperature9.0 pt
-40
85
C
Power dissipation = 1.3W
Ceramic Package
Symbol
Parameter
Min
Typ
Max
Units
Conditions
I
VSS
Power Supply Current (V
SS
)
220
mA
I
MOD
= I
BIAS
= 0mA
P
D
Total Power Dissipation
1200
mW
V
SS
= -5.5V, I
MOD
= I
BIAS
= 0mA,
R
LOAD
= 25
to GND
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
-2.5V
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
t
SU
Data to Clock Setup Time
50
ps
t
H
Hold Time
50
ps
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7925
SONET/SDH 2.5Gb/s Laser Diode Driver
Page 4
G52157-0, Rev 3.2
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
Figure 1: Laser Driver Maximum Case Temperature vs. Modulation Current
Figure 2: Clock and Data Input Structure
Figure 3: Single-Ended Operation
CASE TEMPERATURE vs. MODULATION CURRENT
Modulation Current (mA)
Case Temperature (
o
C)
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
X
X
X
(NCLK)
NDIN
(CLK)
DIN
VREF
+
-
X
(VSS)
-5.2V
(GND)
0V
X
(GND)
0V
50
10pF
2000
3
Nominal VREF Value = -2.5V
All Values Nominal
2000
2k
2k
50
0.1
f
0.1
f
0.1
f
GND
0.1
f
NCLK
CLK
NDIN
DIN
7925
DATA
SOURCE
CLOCK
SOURCE
GND
VSC7925
VITESSE
SEMICONDUCTOR CORPORATION
G52157-0, Rev 3.2
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
VSC7925
SONET/SDH 2.5Gb/s Laser Diode Driver
Figure 4: Control Signals VIP and VIB
Figure 5: Simplified Output Structure
50 mA
60 mA
I (MIB)
I (MIP)
VIP
VIB
2.1V
2.1V
Typical Bias Current v.s. Bias Voltage
Typical Modulation Current v.s. Modulation Voltage
X
X
X
X
X
X
NIOUT
IOUT
X
IBIAS
OUTPUT
DIFF
PAIR
VIB
MIB
MIP
VIP
I
MOD
I
BIAS
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