VITESSE VSC7924KFL, VSC7924KF Datasheet

Preliminary Data Sheet

VITESSE

SEMICONDUCTOR CORPORATION

VSC7924

SONET/SDH 2.5Gb/s Laser Diode Driver

Features Applications

• Rise Times Less Than 100ps

• High-Speed Operation
(Up to 2.5Gb/s NRZ Data)

• Single-Ended Operation

• Single Power Supply

• Direct Access to Modulation and Bias FETs

• Data Density Monitors

• 24-Pin Ceramic Package

• SONET/SDH at 622Mb/s, 1.244Gb/s, and 2.488Gb/s

• Full-Speed Fibre Channel (1.062Gb/s)

General Description

The VSC7924 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 monitor­ing and setting of the current levels. Data inputs accept ECL levels. Data density outputs are provided to allow
the user to adjust the laser bias in high unbalanced data applications.

VSC7924 Block Diagram

DIN

VREF

*TERM

*Terminated to Off-chip Capacitor

VIP

VIB

MK
NMK

NIOUTIOUT

IMOD

MIP

IBIAS

MIB

G52156-0, Rev 3.0 Page 1
05/01/01

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VITESSE

SEMICONDUCTOR CORPORATION

Preliminary Data Sheet

SONET/SDH 2.5Gb/s Laser Diode Drive r

Table 1: Signal Pin Reference

Signal Type Level # Pins Description

DIN In ECL 1 Data Input
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 5 Negative Voltage Rail
GND Pwr Pwr 8 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
VREF In DC 1 Data Input Reference
TERM In DC 1 Data Input Reference
T otal Pin s 24

Table 2: Absolute Maximum Ratings

Symbol Rating Limit

V

SS

T

J

T

STG

Negative Power Supply Voltage VCC to -6.0V
Maximum Junction Temperature -55°C to + 125°C
Storage Temperature -65°C to +150°C

VSC7924

Table 3: ECL Input and Outputs

Symbol Parameter Min Typ Max Units Conditions

V

IN

V

OH

V

OL

Input Voltage Swing 300 800 mV Peak-to-peak, V
ECL Output High Voltage -1200 -700 mV 50Ω to -2.0V
ECL Output Low Voltage -2000 -1600 mV 50Ω to -2.0V

REF

= -1.3V

Table 4: Recommended Operating Conditions

Symbol Parameter Min Typ Max Units Conditions

GND Positive Voltage Rail 0 V
VSS Negative Voltage Rail -5.5 -5.2 -4.9 V
T

Cl

T

J

NOTES: (1) Lower li m i t o f s pecification is ambie nt te m perature and upper limit is cas e t em perature.

Page 2 G52156-0, Rev 3.0

Operational Temperature
Junction Temperature 125 °C

(2) See “Calculation of the Maxim u m Ca s e Temperature” section for detailed maximum te m perature calculations.

© VITESSE SEMICONDUCTOR CORPORATION • 741 Ca l le Pl an o • Camarillo, CA 93012

(1)

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-40 85

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(2)

°C Power dissipation = 1.25W

05/01/01

Preliminary Data Sheet

VITESSE

SEMICONDUCTOR CORPORATION

VSC7924

SONET/SDH 2.5Gb/s Laser Diode Driver

Table 5: Power Diss ipat ion

Symbol Parameter Min Typ Max Units Conditions

I

VSS

P

D

P

DMAX

Power Supply Current (VSS)220mAV
T ot al Power Dissipation 1120 mW

Maximum Power Di ss ip a tio n 1815 mW

V
R

V
I

BIAS

SS
SS

LOAD
SS

= -5.5V, I
= -5.5V, I

= -5.5V, I

= 50mA, I

= 25Ω to GND

T able 6: Laser Driver DC Electrical Specifications

Symbol Parameter Min Typ Max Units Conditions

I

BIAS

I

MOD

V

V

V

IB

IP

OCM

Programmable Laser Bias Current 2 50 mA
Programmabl e Mo du la tio n Cu rr e nt 2 60 mA

+

V

Laser Bias Control Voltage

Laser Modulation Control Voltage

Output Voltage Compliance

GND

-2.2V

SS

2.1

VSS +

2.1

VI

VI

VV

BIAS

MOD

SS

= 50mA

= 60mA

= -5.2V

MOD
MOD

MOD

OUT

= I

BIAS

= I

BIAS

= 60mA,

= 0V

= 0mA
= 0mA,

T able 7: Laser Driver AC Electrical Specifications

Symbol Parameter Min Typ Max Units Conditions

25Ω load, 20%-80%,

tR, t

Output Rise and Fall Times 100 ps

F

15mA < I
I

= 20mA

BIAS

MOD

< 60mA,

Table 8: Package Thermal Specifications

Symbol Parameter Min Typ Max Units Conditions

θ

JCC

Thermal Resistance from junction-to-case 25 °C/W Ceramic Package

G52156-0, Rev 3.0 Page 3
05/01/01

© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012

Tel: (800) VITESSE • FAX: [phone] • Email: [e-mail]

Internet: www.vitesse.com

VITESSE

SEMICONDUCTOR CORPORATION

Preliminary Data Sheet

SONET/SDH 2.5Gb/s Laser Diode Drive r

VSC7924

Calculation of the Maximum Case Temperature

The VSC7924 is designed to operate with a maximum junction temperature of 125°C. The rise from the
case to junction is determined by the power dissip ation of the device. The power dissipation is d etermined by
the V

current plus the operating I

SS

MOD

and I

BIAS

currents.

The power of the chip is determined by the following formula:

P

= (-VSS * ISS) + ((V

D

IOUT – VSS

) * I

MOD

For example with:

V

SS

I

MOD

I

BIAS

V

IBIAS

V

IOUT

=-5.2V
= 40mA
= 20mA
=-2.0V
=-2.0V

= (-5.2 * 220mA) + ((5.2 - 2.0) * 40mA) + ((5.2-- 2.0) * 20mA)

P

D

P

= 1144mW + 128mW + 64mW = 1.336W

D

) + ((V

IBIAS – VSS

) * I

BIAS

)

θ

The thermal rise from junction to case is

* PD. For the ceramic package, θJC = 25°C/W. Thus the ther-

JC

mal rise is:

25°C/W * 1.336W = 33.4°C

The maximum case temperature is:

125°C – 33.4°C = 91.6°C

The absolute maximum power dissipation of the device is at:

V

SS

I

MOD

I

BIAS

V

IBIAS

V

IOUT

= -5.5V
= 60mA
= 50mA
=0V
=0V

= (5.5 * 220mA) + (5.5 * 60mA) + (5.5mA * 50mA) PD= 1.815W

P

D

This will net a maximum junction to case thermal rise of: 1.815W * 25°C/W = 45.4°C

This situation will allow maximum case temperature of: 125°C – 45.4°C = 79.6°C

Page 4 G52156-0, Rev 3.0

© VITESSE SEMICONDUCTOR CORPORATION • 741 Ca l le Pl an o • Camarillo, CA 93012

Tel: (800) VITESSE • FAX: [phone] • Email: [e-mail]

Internet: www.vitesse.com

05/01/01