VITESSE
SEMICONDUCTOR CORPORATION
Advance Product Information
VSC7927
Features
• Rise Times Less Than 100ps
• High Speed Operation
(Up to 2.5 Gb/s NRZ Data)
• Differential or Single-Ended Inputs
• Single Supply
• ECL Compatible Clock and Data Inputs
SDH/SONET 2.5Gb/s
Laser Diode Driver
• Direct Access to Modulation and Bias FET’s
• Data Density Monitors
• On-chip Reclocking Register
• On-chip Mux for Clocked or Non-clocked
Applications
• On-chip 50 Ohm Input Termination: Clock
and Data
Introduction
The VSC7927 is a single 5V supply, 2.5 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 monitor-
ing and setting of the current levels. Data density outputs are provided to allow the user to adjust the laser bias in
high unbalanced data applications. Clock and data inputs are differentially terminated to 50 Ohms.
Applications
• SDH/SONET @ 622Mb/s, 1.244Gb/s, 2.488Gb/s
• Full Speed Fibre Channel (1.062Gb/s)
VSC7927 Block Diagram
MK
NMK
IOUT
NIOUT
DIN
50
Ω
**
DINTERM*
50
Ω
**
NDIN
D Q
M
U
X
IBIAS
DCC
CLK
50
Ω
**
CLKTERM*
50
Ω
**
NCLK
SEL
MIP
*Terminated to Off-chip Capacitor
**On Die Components
VIB
VIP
I
MOD
I
BIAS
MIB
G52201-0, Rev 2.2
10/13/99
©
VITESSE
SEMICONDUCTOR CORPORATION
741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
Page 1
VITESSE
SEMICONDUCTOR CORPORATION
SDH/SONET 2.5 Gb/s
Laser Diode Driver
Table 1: Signal Pin Reference
Signal
DIN, NDIN
MK, NMK
NIOUT
IOUT
VSS
GND
VIP
MIP
VIB
MIB
IBIAS
CLK, NCLK
DINTERM
CLKTERM
DCC
SEL
GND/NC
Total Pins
*
Advance Product Information
VSC7927
Level
ECL
ECL
Type
In
Out
Out
Out
Pwr
Pwr
In
In
In
In
Out
In
In
In
In
In
Pwr
# Pins
2
2
1
1
2
5/6
*
1
1
1
1
1
2
1
1
1
1
7
*
*
Description
Data Input and Data Reference, On-chip 50¾ Termination
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
Laser Bias Output (To Laser Cathode)
Clock Input and Clock Reference, On-chip 50¾ Termination
Data Reference
Clock Reference
Duty Cycle Control, Leave Floating
Clk/Non-clk Data Select
No connection (leave floating or connect to GND)
—
—
Pwr
Pwr
DC
DC
DC
DC
DC
ECL
DC
DC
DC
DC
DC
—
—
24/32
Applicable to 32 pin TQFP package only
Table 2: Mux Select Logic Table
SEL
V
SS
GND
N/C
Clocked Data In
Non-clocked Data In
Non-clocked Data In
Mode Select
Table 3: 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
-55C to + 125C
-65C to +150C
Page 2
©
VITESSE
SEMICONDUCTOR CORPORATION
741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
G52201-0, Rev 2.2
10/13/99
VITESSE
SEMICONDUCTOR CORPORATION
Advance Product Information
VSC7927
Table 4: High Speed Inputs and ECL Outputs
Symbol
V
IN
V
CM
V
OH
V
OL
V
IN
SDH/SONET 2.5Gb/s
Laser Diode Driver
Parameter
Single-ended Input Voltage Swing
Differential Input Common Mode Range
ECL Output High Voltage
ECL Output Low Voltage
On-Chip Terminations
Min
300
-2.3
-1200
Max
1500
-1.3
Units
mVp-p
V
mV
mV
Ohms
Conditions
V
CM
= -2.0V
V
SS
= -5.2V
50 Ohms to -2.0V
50 Ohms to -2.0V
—
—
-1600
65
—
35
Table 5: Recommended Operating Conditions
Symbol
GND
VSS
Tc
l
Parameter
Positive Voltage Rail
Negative Voltage Rail
*Operational Temperature
Min
—
-5.5
-40
Typ
0
-5.2
Max
—
-4.9
85**
Units
V
V
C
Conditions
—
—
Power dissipation = 1.3W
—
125
C
—
Tj
Junction Temperature
*Lower limit of specification is ambient temperature and upper limit is case temperature.
**See section “Calculation of the Maximum Case Temperature” for detailed maximum temperature calculations.
Table 6: Power Dissipation
Symbol
I
VSS
Pd
—
—
Parameter
Power Supply Current (VSS)
Total Power Dissipation
Min
—
—
Typ
—
-
—
Max
120
700
Units
mA
mW
Conditions
V
SS
= -5.5, I
MOD
= I
BIAS
= 0 mA,
MK/NMK open circuit
V
SS
= -5.5, I
MOD
= I
BIAS
= 0 mA,
Rload = 25 Ohms to GND, MK/NMK
terminated 50Ω to -2V
Table 7: 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
Typ
—
—
—
—
GND -3V
Max
100
100
V
SS
+ 2.1
V
SS
+ 2.1
Units
mA
mA
V
V
V
Conditions
—
—
I
BIAS
= 50 mA
I
MOD
= 60 mA
V
SS
= -5.2V
—
—
—
—
G52201-0, Rev 2.2
10/13/99
©
VITESSE
SEMICONDUCTOR CORPORATION
741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
Page 3
VITESSE
SEMICONDUCTOR CORPORATION
SDH/SONET 2.5 Gb/s
Laser Diode Driver
Table 8: Laser Driver AC Electrical Specifications
Symbol
t
r
t
f
t
su
t
h
Advance Product Information
VSC7927
Parameter
Output Rise and Fall
Times
t Setup Data to Clock
t Hold
Min
—
—
20
Typ
—
50
50
Max
100
Units
ps
ps
ps
Conditions
25 Ohm load, 20%-80%,
20mA < I
MOD
< 60mA,
I
BIAS
= 60mA
90
—
—
—
Table 9: 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
Page 4
©
VITESSE
SEMICONDUCTOR CORPORATION
741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
G52201-0, Rev 2.2
10/13/99
VITESSE
SEMICONDUCTOR CORPORATION
Advance Product Information
VSC7927
Calculation of the Maximum Case Temperature
SDH/SONET 2.5Gb/s
Laser Diode Driver
The VSC7927 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
=
(-V
SS
*
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
P
D
=
P
D
=
=
=
=
=
=
-5.2V
40mA
20mA
-2.0V
-2.0V
(-5.2 *
150mA)
+ ((5.2
- 2.0)
*
40mA)
+ ((5.2
-
- 2.0)
*
20mA)
780mW + 128mW + 64mW = 972mW
The thermal rise from junction to case is
θ
JC
*
P
D
. For the metal glass package,
θ
JC
= 32 °C/W. Thus the
thermal rise is:
32°C/W * 1.336W = 31.1°C
The maximum case temperature is:
125°C – 31.1°C = 93.9°C
The absolute maximum power dissipation of the device is at:
V
SS
I
MOD
I
BIAS
V
IBIAS
V
IOUT
P
D
=
=
=
=
=
=
-5.5V
60mA
50mA
0V
0V
P
D
=
1.43W
(5.5 *
150mA)
+ (5.5 *
60mA)
+ (5.5mA *
50mA)
This will net a maximum junction to case thermal rise of: 1.43W * 32°C/W = 45.8°C
This situation will allow maximum case temperature of: 125°C – 58°C = 79.2°C
G52201-0, Rev 2.2
10/13/99
©
VITESSE
SEMICONDUCTOR CORPORATION
741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
Page 5
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