VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
G52357-0, Rev 3.2
Page 1
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
Features
Applications
General Description
The VSC7940 is a single 5V supply laser diode driver specially designed for SONET/SDH applications up
to 3.125Gb/s. External resistors set a wide range of bias and modulation currents for driving the laser. Data and
clock inputs accept differential PECL signals. The Automatic Power Control (APC) loop maintains a constant
average optical power over temperature and lifetime. The dominant pole of the APC loop can be controlled with
an external capacitor. Other features include enable/disable control, programmable slow-start circuit to set laser
turn-on delay, and failure-monitor output to indicate when the APC loop is unable to maintain the average opti-
cal power. The VSC7940 is available in die form or in a 32-pin TQFP package.
Block Diagram
Power Supply: 5V
5%
DC-Coupled to Laser Diode
Programmable Modulation Current: 5mA to 100mA
Programmable Bias Current: 1mA to 100mA
Enable/Disable Control
Automatic Optical Average Power Control
Modulation and Bias Current Monitors
Q
S E T
CLR
Q
D
M U X
M O D S E T
BIASMAX
C A P C
A P C
A P C S E T
L AT C H
1nF
MODMON
MD
FAIL
BIAS
BIASMON
DATA+
DATA-
CLK+
CLK-
ENABLE
DISABLE
V
CC
V
CC
V
CC
IOUT+
IOUT-
V
CC
R
F
C
F
SONET/SDH at 622Mb/s, 1.244Gb/s,
2.488Gb/s, 3.125Gb/s
Full-Speed Fibre Channel (1.062Gb/s)
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Page 2
G52357-0, Rev 3.2
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
Electrical Characteristics
Table 1: AC Specifications
AC specifications are guaranteed by design and characterization. Typical values are for 5V operation.
NOTES: (1) Measured with 622Mb/s 0-1 pattern, LATCH=high. (2) PWD = (wider pulse - narrower pulse) / 2).
Table 2: DC Specifications
Symbol
Parameter
Min
Typ
Max
Units
Conditions
t
SU
Input Latch Setup Time
100
ps
LATCH=high
t
H
Input Latch Hold Time
100
ps
LATCH=high
Enable/Start-up Delay
250
ns
t
R
Output Rise Time
TBD
TBD
ps
20% to 80%
t
F
Output Fall Time
TBD
TBD
ps
20% to 80%
PWD
Pulse Width Distortion
10
50
ps
See Notes 1, 2
CID
MAX
Maximum Consecutive Identical Digits
80
bits
t
J
Jitter Generation
7
20
ps
p-p
Jitter BW=12kHz to 20MHz,
0-1 pattern.
Symbol
Parameter
Min
Typ
Max
Units
Conditions
V
SS
Power Supply Voltage
4.75
5.0
5.25
V
I
CC
Power Supply Current
TBD
45
mA
R
MODSET
=7.3k
R
BIASMAX
=4.8k
I
BIAS
and I
MOD
excluded, V
CC
=5V
I
BIAS
Bias Current Range
1
100
mA
Voltage at BIAS pin=(V
CC
-1.6)
I
BIAS-OFF
Bias Off Current
100
A
ENABLE=low or
DISABLE=high
(1)
S
BIAS
Bias Current Stability
230
ppm/
C
APC open loop. I
BIAS
=100mA
900
APC open loop. I
BIAS
=1mA
Bias Current Absolute Accuracy
15
%
Refers to part-to-part variation
VR
MD
Monitor Diode Reverse Bias Voltage
1.5
V
I
MD
Monitor Diode Reverse Current Range
18
1000
A
Monitor Diode Bias Setpoint Stability
-480
-50
480
ppm/
C
I
MD
=1mA
(2)
90
I
MD
=18A
(2)
Monitor Diode Bias Absolute Accuracy
-15
15
%
Refers to part-to-part variation
I
MOD
Modulation Current Range
5
100
mA
I
MOD-OFF
Modulation Off Current
200
A
ENABLE=low or
DISABLE=high
(1)
Modulation Current Absolute Accuracy
15
%
See Note 2
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
G52357-0, Rev 3.2
Page 3
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
NOTES: (1) Both I
BIAS
and I
MOD
will turn off if any of the current set pins are grounded. (2) Assumes laser diode to monitor diode transfer func-
tion does not change with temperature.
Table 3: PECL and TTL/CMOS Input
/
Output Specifications
Absolute Maximum Ratings
(1)
Power Supply Voltage (V
CC
)............................................................................................................. -0.5V to +7V
Current into BIAS.....................................................................................................................-20mA to +150mA
Current into OUT+, OUT- ...............................................................................................................................TBD
Current into MD ............................................................................................................................. -5mA to +5mA
Current into FAIL ......................................................................................................................... -10mA to 30mA
Voltage at DATA+, DATA-, CLK+, CLK-, ENABLE, LATCH......................................... -0.5V to (V
CC
+ 0.5V)
Voltage at APCFILT, MODSET, BIASMAX, APCSET, MD, FAIL ............................................. -0.5V to +3.0V
Voltage at OUT+, OUT- ..................................................................................................... -0.5V to (V
CC
+ 1.5V)
Voltage at BIAS .................................................................................................................. -0.5V to (V
CC
+ 0.5V)
Continuous Power Dissipation (T
A
= +85C, TQFP derate 20.8mW/C above +85C) .........................1350mW
Operating Junction Temperature Range ...................................................................................... -55C to +150C
Storage Temperature Range ........................................................................................................ -65C to +165C
NOTE: (1) CAUTION: Stresses listed under "Absolute Maximum Ratings" may be applied to devices one at a time without caus-
ing permanent damage. Functionality at or above the values listed is not implied. Exposure to these values for extended
periods may affect device reliability.
Recommended Operating Conditions
Positive Voltage Rail (V
CC
).............................................................................................................................. +5V
Negative Voltage Rail (GND) ............................................................................................................................ 0V
Ambient Temperature Range (T
A
).................................................................................................. -40C to +85C
Modulation Current Stability
-480
-50
480
ppm/
C
I
MOD
=60mA
250
I
MOD
=5mA
A
BIAS
BIASMON to I
BIAS
Gain
37
I
BIAS
/I
BIASMON
A
MOD
MODMON to I
MON
Gain
29
I
MOD
/I
MODMON
Symbol
Parameter
Min
Typ
Max
Units
Conditions
V
ID
Differential Input Voltage
100
1600
mV
p-p
(DATA+)-(DATA-)
V
ICM
Common-Mode Input Voltage
V
CC
-
1.49
V
CC
-
1.32
V
CC
-
V
ID
/4
V
PECL-compatible
I
IN
Clock and Data Input Current
-1
10
mA
V
IH
TTL Input High Voltage (ENABLE, LATCH)
2.0
V
V
IL
TTL Input Low Voltage (ENABLE, LATCH)
0.8
V
TTL Output High Voltage (FAIL)
2.4
V
CC
-
0.3
V
CC
V
Sourcing 50A
TTL Output Low Voltage (FAIL)
0.1
0.44
V
Sinking 100A
Symbol
Parameter
Min
Typ
Max
Units
Conditions
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Page 4
G52357-0, Rev 3.2
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
Bare Die Pad Descriptions
Figure 1: Pad Assignments
VSC7940
Pad 8
CLK-
Pad 7
CLK+
Pad 6
VCC1
Pad 5
GND1
Pad 4
VCC1
Pad 3
DATA-
Pad 2
DATA+
Pad 1
VCC1
(Pin 1)
(Pin 2)
(Pin 3)
(Pin 4)
(Pin 6)
(Pin 7)
(Pin 8)
(Pin 9)
(Pin 10)
(Pin 11)
(Pin 12)
(Pin 13)
(Pin 15)
(Pin 14)
(Pin 16)
(Pin 17)
(Pin 32)
(Pin 31)
(Pin 30)
(Pin 29)
(Pin 28)
(Pin 26)
(Pin 27)
(Pin 25)
(Pin 5)
(Pin 18)
(Pin 19)
(Pin 20)
(Pin 21)
(Pin 22)
(Pin 23)
(Pin 24)
Pad 48
GND1
Pad 47
GND2
Pad 46
VCC2
Pad 45
BIASMAX
20
m
(0.0008")
2233
m
(0.0879")
1773
m (0.0698")
75
m
(0.0030")
Pad 44
MODSET
Pad 43
GND2
Pad 42
APCSET
Pad 41
RESERVED
Pad 40
GND2
Pad 39
PB_GND
Pad 38
GND3
Pad 37
PB_GND
Pad 36
CAPC
Pad 35
VCC3
Pad 34
GND3
Pad 10
GND1
Pad 11
LATCH
Pad 12
ENABLE
Pad 13
DISABLE
Pad 14
GND1
Pad 15
BIASMON
Pad 16
MODMON
Pad 17
FAIL
Pad 18
GND4
Pad 19
PB_GND
Pad 20
APCFILT
Pad 21
GND4
Pad 22
VCC4
Pad 23
BIAS
Pad 9
VCC1
Pad 25
VCC4
Pad 26
DB_OUT+
Pad 27
OUT+
Pad 28
OUT-
Pad 29
DB_OUT-
Pad 30
VCC4
Pad 31
GND4
Pad 32
GND3
Pad 33
MD
Pad 24
PB_GND1
Die Size:
1773
m x 2233
m (0.0698" x 0.0879")
Die Thickness:
625
m (0.0246")
Pad Pitch:
115
m (0.0045")
Pad to Pad Clearance:
20
m (0.0008")
Pad Passivation Opening: 95
m x 95
m (0.0037" x 0.0037")
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
G52357-0, Rev 3.2
Page 5
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
Table 4: Pad Coordinates
Signal
Name
Pad
No.
Coordinates (m)
Signal
Name
Pad
No.
Coordinates (m)
X
Y
X
Y
VCC1
1
(Pin 1)
1211.025
1995.05
VCC4
25
(Pin 18)
406.025
80.95
DATA+
2
(Pin 2)
1096.025
1995.05
DB_OUT+
26
521.025
80.95
DATA-
3
(Pin 3)
981.025
1995.05
OUT+
27
(Pin 19)
636.025
80.95
VCC1
4
(Pin 4)
866.025
1995.05
OUT
28
(Pin 20)
751.025
80.95
GND1
5
751.025
1995.05
DB_OUT
29
866.025
80.95
VCC1
6
636.025
1995.05
VCC4
30
(Pin 21)
981.025
80.95
CLK+
7
(Pin 5)
521.025
1995.05
GND4
31
(Pin 22)
1096.025
80.95
CLK-
8
(Pin 6)
406.025
1995.05
GND3
32
(Pin 23)
1211.025
80.95
VCC1
9
(Pin 7)
291.025
1995.05
MD
33
(Pin 24)
1326.025
80.95
GND1
10
80.95
1784.975
GND3
34
1535.05
289.975
LATCH
11
(Pin 8)
80.95
1669.975
VCC3
35
(Pin 25)
1535.05
404.975
ENABLE
12
(Pin 9)
80.95
1554.975
CAPC
36
(Pin 26)
1535.05
519.975
DISABLE
13
(Pin 10)
80.95
1439.975
PB_GND
37
1535.05
634.975
GND1
14
80.95
1324.975
GND3
38
(Pin 27)
1535.05
749.975
BIASMON
15
(Pin 11)
80.95
1209.975
PB_GND
39
1535.05
864.975
MODMON
16
(Pin 12)
80.95
1094.975
GND2
40
1535.05
979.975
FAIL
17
(Pin 13)
80.95
979.975
RESERVED
41
(Pin 28)
1535.05
1094.975
GND4
18
80.95
864.975
APCSET
42
(Pin 29)
1535.05
1209.975
PB_GND
19
80.95
749.975
GND2
43
1535.05
1324.975
APCFILT
20
(Pin 14)
80.95
634.975
MODSET
44
(Pin 30)
1535.05
1439.975
GND4
21
(Pin 15)
80.95
519.975
BIASMAX
45
(Pin 31)
1535.05
1554.975
VCC4
22
(Pin 16)
80.95
404.975
VCC2
46
(Pin 32)
1535.05
1669.975
BIAS
23
(Pin 17)
80.95
289.975
GND2
47
1535.05
1784.975
PB_GND
24
291.025
80.95
GND1
48
1336.025
1995.05
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