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PDF VSC7939 Data sheet ( Hoja de datos )
| Número de pieza | VSC7939 | |
| Descripción | Laser Diode Driver | |
| Fabricantes | Vitesse Semiconductor | |
| Logotipo |  |
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VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7939
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Features
• Power Supply: 3.3V or 5V ±5%
• AC-Coupled to Laser Diode
• Programmable Modulation Current: 5mA to 60mA
• Programmable Bias Current: 1mA to 100mA
• Enable /Disable Control
• Typical Rise/Fall Times of 60ps
• Automatic Optical Average Power Control
• Supply Current of 33mA at 3.3V
Applications
• SONET/SDH at 622Mb/s, 1.244Gb/s,
2.488Gb/s, 3.125Gb/s
• Full-Speed Fibre Channel (1.062Gb/s)
General Description
The VSC7939 is a single 3.3V or 5V supply laser diode driver specially designed for SONET/SDH applica-
tions 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 con-
trolled with an external capacitor. Other features include enable/disable control, short-circuit protection for the
modulation and bias inputs, short rise and fall times, 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 optical power. The
VSC7939 is available in die form or in a 32-pin TQFP package.
Block Diagram
3.3V Operation
VCC
DATA+
DATA-
CLK+
CLK-
ENABLE
DISABLE
D SETQ
CLR Q
LATCH
MUX
IOUT+
IOUT-
CD
VCC
CF
RF
BIAS
VCC
MODMON
APC
MD
FAIL
MODSET BIASMAX CAPC APCSET
VCC
BIASMON
1nF
G52350-0, Rev 3.2
02/26/01
© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected]
Internet: www.vitesse.com
Page 1
1 page  
www.DataSheet4U.com
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7939
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Bare Die Pad Descriptions
Figure 1: Pad Assignments
1773µm (0.0698")
Pad 12
GND1
Pad 11
VCC1
(Pin 7)
Pad 10
CLK-
(Pin 6)
Pad 9
CLK+
(Pin 5)
Pad 8
VCC1
Pad 7
GND1
Pad 6
VCC1
(Pin 4)
Pad 5
DATA-
(Pin 3)
Pad 4
DATA+
(Pin 2)
Pad 3
VCC1
(Pin 1)
Pad 2
GND1
Pad 1
GND2
Pad 13 (Pin 8)
LATCH
Pad 14
ENABLE
(Pin 9)
Pad 15
DISABLE
(Pin 10)
Pad 16
GND1
Pad 17
BIASMON
(Pin 11)
2233µm
(0.0879")
Pad 18 (Pin 12)
MODMON
Pad 19 (Pin 13)
FAIL
Pad 20
GND4
Pad 21
PB_GND
Pad 22 (Pin 14)
APCFILT
VSC7939
(Pin 32) Pad 48
VCC2
(Pin 31)
Pad 47
BIASMAX
(Pin 30) Pad 46
MODSET
Pad 45
GND2
(Pin 29) Pad 44
APCSET
(Pin 28) Pad 43
RESERVED
Pad 42
GND3
Pad 41
PB_GND
(Pin 27)
Pad 40
GND3
Pad 39
PB_GND
Pad 23 (Pin 15)
GND4
(Pin 26) Pad 38
CAPC
Pad 24
VCC4
(Pin 16)
(Pin 25) Pad 37
VCC3
Pad 25
BIAS (Pin 17)
(Pin 18)
(Pin 19)
Pad 26 Pad 27 Pad 28 Pad 29
PB_GND1 VCC4 DB_OUT+ OUT+
(Pin 20)
Pad 30
OUT-
Pad 31
DB_OUT-
(Pin 21)
Pad 32
VCC4
(Pin 22)
Pad 33
GND4
(Pin 23)
Pad 34
GND3
(Pin 24)
Pad 35
MD
Pad 36
GND3
20µm
(0.0008")
Die Size:
1773µm x 2233µm (0.0698" x 0.0879")
Die Thickness:
625µm (0.0246")
Pad Pitch:
115µm (0.0045")
Pad Size:
95µm x 95µm (0.0037" x 0.0037")
Pad to Pad Clearance:
20µm (0.0008")
Pad Passivation Opening: 95µm x 95µm (0.0037" x 0.0037")
Scribe Size:
75µm (0.0030")
75µm
(0.0030")
G52350-0, Rev 3.2
02/26/01
© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012
Internet: www.vitesse.com
Page 5
5 Page 
www.DataSheet4U.com
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7939
SONET/SDH 3.125Gb/s
Laser Diode Driver with Automatic Power Control
Laser Diode Interface
An RC shunt network should be placed at the laser output interface. The sum of the resistor placed at the
output and the laser diode resistance should be 25Ω. For example, if the laser diode has a resistance of 5Ω, a
20Ω resistor should be placed in series with the laser. For optimal performance, a bypass capacitor should be
placed close to the laser anode.
A “snubber network” consisting of a capacitor CF and resistor RF should be placed at the laser output to
minimize reflections from the laser (see Block Diagram). Suggested values for these components are 80Ω and
2pF, respectively, however, these values should be adjusted until an optical output waveform is obtained.
Reducing Pattern-Dependent Jitter
Three design values significantly affect pattern-dependent jitter; the capacitor at CAPC, the pull-up induc-
tor at the output (LP), and the AC-coupling capacitor at the output (CD). As previously stated, the recommended
value for the capacitor at CAPC is 0.1µF. This results in a 10kHz loop bandwidth which makes the pattern-
dependent jitter from the APC loop negligible.
For 2.5Gb/s data rates, the recommended value for CD is 0.056µF. The time constant at the output is domi-
nated by LP. The variation in the peak voltage should be less that 12% of the average voltage over the maximum
consecutive identical digit (CID) period. The following equation approximates this time constant for a CID
period, t, of 100UI = 40ns:
τLP = -t / ln(1-12%) = 7.8t = LP / 25Ω
Therefore, the inductor LP should be a 7.8µH SMD ferrite bead inductor for this case.
Input/Output Considerations
Although the VSC7939 is PECL-compatible, this is not required to drive the device. The inputs must only
meet the common-mode voltage and differential voltage swing specifications.
Power Consumption
The following equation provides the device supply current (IS) in terms of quiescent current (IQ), modula-
tion current (IMOD), and bias current (IBIAS):
IS = IQ + 0.47 * IMOD + 0.15 * IBIAS
For 3.3V operation, IQ is 15mA. For 5V operation, IQ is 20mA.
This equation may be used to determine the estimated power dissipation:
PDIS = VCC * IS
For example, if the device were operated at 3.3V with a 30mA modulation current and a 10mA bias current,
the supply current would be:
IS = 15mA + 0.47 * 30mA + 0.15 * 10mA = 31
This corresponds to a power dissipation of 3.3V * 31mA = 102mW.
G52350-0, Rev 3.2
02/26/01
© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012
Internet: www.vitesse.com
Page 11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet VSC7939.PDF ] | |
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