VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
Features
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Applications
• SONET/SDH at 622Mb/s, 1.244Gb/s,
2.488Gb/s, 3.125Gb/s
• Full-Speed Fibre Channel (1.062Gb/s)
• 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
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
V
CC
L AT C H
IOUT+
IOUT-
MUX
DATA+
DATA-
CLK+
CLK-
CLR
Q
BIAS
SET
Q
C
F
R
F
V
CC
D
V
CC
ENABLE
DISABLE
V
CC
MODMON
BIASMON
APC
MD
FAIL
1nF
MODSET
BIASMAX
CAPC
APCSET
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
Page 1
VITESSE
SEMICONDUCTOR CORPORATION
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Preliminary Data Sheet
VSC7940
Electrical Characteristics
Table 1: AC Specifications
AC specifications are guaranteed by design and characterization. Typical values are for 5V operation.
Symbol
t
SU
t
H
Parameter
Input Latch Setup Time
Input Latch Hold Time
Enable/Start-up Delay
Min
100
100
Typ
Max
Units
ps
ps
Conditions
LATCH=high
LATCH=high
250
TBD
TBD
10
80
7
20
TBD
TBD
50
ns
ps
ps
ps
bits
ps
p-p
Jitter BW=12kHz to 20MHz,
0-1 pattern.
20% to 80%
20% to 80%
See Notes 1, 2
t
R
t
F
PWD
CID
MAX
t
J
Output Rise Time
Output Fall Time
Pulse Width Distortion
Maximum Consecutive Identical Digits
Jitter Generation
NOTES: (1) Measured with 622Mb/s 0-1 pattern, LATCH=high. (2) PWD = (wider pulse - narrower pulse) / 2).
Table 2: DC Specifications
Symbol
V
SS
I
CC
I
BIAS
I
BIAS-OFF
S
BIAS
Parameter
Power Supply Voltage
Power Supply Current
Bias Current Range
Bias Off Current
Bias Current Stability
Bias Current Absolute Accuracy
Min
4.75
Typ
5.0
TBD
Max
5.25
45
100
100
Units
V
Conditions
R
MODSET
=7.3kΩ
mA
mA
µA
ppm/°C
%
V
1000
-50
90
-15
5
15
100
200
±15
480
µA
ppm/°C
%
mA
µA
%
ENABLE=low or
DISABLE=high
(1)
See Note 2
I
MD
=1mA
(2)
I
MD
=18µA
(2)
Refers to part-to-part variation
R
BIASMAX
=4.8kΩ
I
BIAS
and I
MOD
excluded, V
CC
=5V
Voltage at BIAS pin=(V
CC
-1.6)
ENABLE=low or
DISABLE=high
(1)
APC open loop. I
BIAS
=100mA
APC open loop. I
BIAS
=1mA
Refers to part-to-part variation
1
230
900
±15
1.5
18
-480
VR
MD
I
MD
Monitor Diode Reverse Bias Voltage
Monitor Diode Reverse Current Range
Monitor Diode Bias Setpoint Stability
Monitor Diode Bias Absolute Accuracy
I
MOD
Modulation Current Range
I
MOD-OFF
Modulation Off Current
Modulation Current Absolute Accuracy
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
G52357-0, Rev 3.2
05/11/01
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
Symbol
Parameter
Modulation Current Stability
A
BIAS
A
MOD
BIASMON to I
BIAS
Gain
MODMON to I
MON
Gain
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Min
-480
Typ
-50
250
37
29
Max
480
Units
ppm/°C
Conditions
I
MOD
=60mA
I
MOD
=5mA
I
BIAS
/I
BIASMON
I
MOD
/I
MODMON
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
Symbol
V
ID
V
ICM
I
IN
V
IH
V
IL
Parameter
Differential Input Voltage
Common-Mode Input Voltage
Clock and Data Input Current
TTL Input High Voltage (ENABLE, LATCH)
TTL Input Low Voltage (ENABLE, LATCH)
TTL Output High Voltage (FAIL)
TTL Output Low Voltage (FAIL)
Min
100
V
CC
-
1.49
-1
2.0
Typ
V
CC
-
1.32
Max
1600
V
CC
-
V
ID
/4
10
0.8
Units
mV
p-p
V
mA
V
V
V
V
Conditions
(DATA+)-(DATA-)
PECL-compatible
2.4
0.1
V
CC
-
0.3
V
CC
0.44
Sourcing 50µA
Sinking 100µA
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
= +85°C, TQFP derate 20.8mW/°C above +85°C) .........................1350mW
Operating Junction Temperature Range ...................................................................................... -55°C to +150°C
Storage Temperature Range ........................................................................................................ -65°C to +165°C
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
).................................................................................................. -40°C to +85°C
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
Page 3
VITESSE
SEMICONDUCTOR CORPORATION
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Preliminary Data Sheet
VSC7940
Bare Die Pad Descriptions
Figure 1: Pad Assignments
1773µm (0.0698")
Pad 9
VCC1
Pad 10
GND1
Pad 11
LATCH
Pad 12
ENABLE
(Pin 7)
Pad 8
CLK-
(Pin 6)
Pad 7
CLK+
(Pin 5)
Pad 6
VCC1
Pad 5
GND1
Pad 4
VCC1
(Pin 4)
Pad 3
DATA-
(Pin 3)
Pad 2
DATA+
(Pin 2)
Pad 1
VCC1
(Pin 1)
Pad 48
GND1
Pad 47
GND2
Pad 46
VCC2
Pad 45
BIASMAX
Pad 44
MODSET
Pad 43
GND2
(Pin 29)
Pad 42
APCSET
Pad 41
RESERVED
Pad 40
GND2
Pad 39
PB_GND
(Pin 27)
Pad 38
GND3
Pad 37
PB_GND
(Pin 26)
Pad 36
CAPC
Pad 35
VCC3
Pad 34
GND3
(Pin 8)
(Pin 32)
20µm
(0.0008")
(Pin 9)
(Pin 31)
Pad 13
(Pin 10)
DISABLE
Pad 14
GND1
Pad 15 (Pin 11)
BIASMON
Pad 16 (Pin 12)
MODMON
(Pin 30)
(Pin 28)
2233µm
(0.0879")
VSC7940
Pad 17
FAIL
Pad 18
GND4
Pad 19
PB_GND
(Pin 13)
Pad 20
APCFILT (Pin 14)
Pad 21
GND4
Pad 22
VCC4
Pad 23
BIAS
(Pin 15)
(Pin 16)
(Pin 25)
(Pin 17)
(Pin 18)
Pad 24
PB_GND1
Pad 25
VCC4
Pad 26
DB_OUT+
(Pin 19)
Pad 27
OUT+
(Pin 20)
Pad 28
OUT-
Pad 29
DB_OUT-
(Pin 21)
Pad 30
VCC4
(Pin 22)
Pad 31
GND4
(Pin 23)
Pad 32
GND3
(Pin 24)
Pad 33
MD
Die Size:
Die Thickness:
Pad Pitch:
Pad to Pad Clearance:
Pad Passivation Opening:
1773µm x 2233µm (0.0698" x 0.0879")
625µm (0.0246")
115µm (0.0045")
20µm (0.0008")
95µm x 95µm (0.0037" x 0.0037")
µ
75µm
(0.0030")
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
G52357-0, Rev 3.2
05/11/01
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
Table 4: Pad Coordinates
Signal
Name
VCC1
DATA+
DATA-
VCC1
GND1
VCC1
CLK+
CLK-
VCC1
GND1
LATCH
ENABLE
DISABLE
GND1
BIASMON
MODMON
FAIL
GND4
PB_GND
APCFILT
GND4
VCC4
BIAS
PB_GND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
(Pin 14)
(Pin 15)
(Pin 16)
(Pin 17)
(Pin 11)
(Pin 12)
(Pin 13)
(Pin 8)
(Pin 9)
(Pin 10)
(Pin 5)
(Pin 6)
(Pin 7)
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Pad
No.
(Pin 1)
(Pin 2)
(Pin 3)
(Pin 4)
Coordinates (µm)
X
1211.025
1096.025
981.025
866.025
751.025
636.025
521.025
406.025
291.025
80.95
80.95
80.95
80.95
80.95
80.95
80.95
80.95
80.95
80.95
80.95
80.95
80.95
80.95
291.025
Y
1995.05
1995.05
1995.05
1995.05
1995.05
1995.05
1995.05
1995.05
1995.05
1784.975
1669.975
1554.975
1439.975
1324.975
1209.975
1094.975
979.975
864.975
749.975
634.975
519.975
404.975
289.975
80.95
Signal
Name
VCC4
DB_OUT+
OUT+
OUT–
DB_OUT–
VCC4
GND4
GND3
MD
GND3
VCC3
CAPC
PB_GND
GND3
PB_GND
GND2
RESERVED
APCSET
GND2
MODSET
BIASMAX
VCC2
GND2
GND1
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
Pad
No.
(Pin 18)
(Pin 19)
(Pin 20)
(Pin 21)
(Pin 22)
(Pin 23)
(Pin 24)
(Pin 25)
(Pin 26)
(Pin 27)
Coordinates (µm)
X
406.025
521.025
636.025
751.025
866.025
981.025
1096.025
1211.025
1326.025
1535.05
1535.05
1535.05
1535.05
1535.05
1535.05
1535.05
Y
80.95
80.95
80.95
80.95
80.95
80.95
80.95
80.95
80.95
289.975
404.975
519.975
634.975
749.975
864.975
979.975
1094.975
1209.975
1324.975
1439.975
1554.975
1669.975
1784.975
1995.05
(Pin 28)
(Pin 29)
(Pin 30)
(Pin 31)
(Pin 32)
1535.05
1535.05
1535.05
1535.05
1535.05
1535.05
1535.05
1336.025
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
Page 5
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