SRDA3.3-4TE - Semtech - Datasheet.Live

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SRDA3.3-4 THRU SRDA12-4

RailClampÒ

Low Capacitance TVS Diode Array

Description Features

Circuit Diagram Schematic & PIN Configuration

Revision 9/2000

RailClamps are surge rated diode arrays designed to

protect high speed data interfaces. The SR series has

been specifically designed to protect sensitive compo-

nents which are connected to data and transmission

lines from overvoltage caused by ESD (electrostatic

discharge), EFT (electrical fast transients), and light-

ning.

The unique design of the SRDA series devices incorpo-

rates surge rated, low capacitance steering diodes and

a TVS diode in a single package. During transient

conditions, the steering diodes direct the transient to

either the positive side of the power supply line or to

ground. The internal TVS diode prevents over-voltage

on the power line, protecting any downstream compo-

nents.

The low capacitance array configuration allows the user

to protect two high-speed data or transmission lines.

The low inductance construction minimizes voltage

overshoot during high current surges. Applications

Mechanical Characteristics

uUSB Power & Data Line Protection

uT1/E1 secondary IC Side Protection

uT3/E3 secondary IC Side Protection

uHDSL, IDSL secondary IC Side Protection

uVideo Line Protection

uMicrocontroller Input Protection

uBase stations

uI2C Bus Protection

uTransient protection for high-speed data lines to

IEC 61000-4-2 (ESD) 15kV (air), 8kV (contact)

IEC 61000-4-4 (EFT) 40A (5/50ns)

IEC 61000-4-5 (Lightning) 24A (8/20µs)

uArray of surge rated diodes with internal TVS diode

uProtects four I/O lines & power supply line

uLow capacitance (<15pF) for high-speed interfaces

uLow operating & clamping voltages

uSolid-state technology

uJEDEC SO-8 package

uUL 497B listed

uMolding compound flammability rating: UL 94V-0

uMarking : Part number, date code, logo

uPackaging : Tube or Tape and Reel per EIA 481

I/O

REF 2

I/O

REF 1

S0-8 (Top View)

REF1

I/O 1 I/O 2 I/O 3 I/O 4

REF2

2ã 2000 Semtech Corp. www.semtech.com

PROTECTION PRODUCTS

SRDA3.3-4 THRU SRDA12-4

Absolute Maximum Rating

Electrical Characteristics

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Note:

(1) The SRDA3.3-4 is constructed using Semtechs propri-

etary EPD process technology. See applications section for

more information.

ã 2000 Semtech Corp. www.semtech.com

PROTECTION PRODUCTS

SRDA3.3-4 THRU SRDA12-4

4-50ADRS

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Electrical Characteristics (continued)

4ã 2000 Semtech Corp. www.semtech.com

PROTECTION PRODUCTS

SRDA3.3-4 THRU SRDA12-4

Typical Characteristics

Non-Repetitive Peak Pulse Power vs. Pulse Time Power Derating Curve

0.01

0.1

0.1 1 10 100 1000

Pulse Duration - tp (µs)

Peak Pulse Power - P

(kW)

100

110

0 25 50 75 100 125 150

Ambi ent Tem p er at u re - TA (oC)

% of Rated Power or I

Clamping Voltage vs. Peak Pulse Current

100

110

0 5 10 15 20 25 30

Time (µs)

Percent of I

e-t

td = IPP/2

Waveform

Parameters:

tr = 8µs

td = 20µs

Pulse Waveform

0 5 10 15 20 25 30 35

Peak Pulse Current - IPP (A)

Clamping Voltage - V

(V)

SRDA05-4

SRDA3.3-4

Waveform

Parameters:

tr = 8µs

td = 20µs

SRDA12-4

Variation of Capacitance vs. Reverse Voltage Forward Voltage vs. Forward Current

-14

-12

-10

-8

-6

-4

-2

0123456

Reverse Voltage (V)

% Change in Capacitance

I/O to GND

f = 1MHz

0 5 10 15 20 25 30 35 40 45 50

Forward Current - IF (A)

Forward Voltage - V

(V)

Waveform

Parameters:

tr = 8µs

td = 20µs

ã 2000 Semtech Corp. www.semtech.com

PROTECTION PRODUCTS

SRDA3.3-4 THRU SRDA12-4

Device Connection Options for Protection of Four

High-Speed Lines

The SRDA TVS is designed to protect four data lines

from transient overvoltages by clamping them to a

fixed reference. When the voltage on the protected

line exceeds the reference voltage (plus diode VF) the

steering diodes are forward biased, conducting the

transient current away from the sensitive circuitry.

Data lines are connected at pins 1, 4, 6 and 7. The

negative reference is connected at pins 5 & 8. These

pins should be connected directly to a ground plane on

the board for best results. The path length is kept as

short as possible to minimize parasitic inductance.

The positive reference is connected at pins 2 and 3.

The options for connecting the positive reference are

as follows:

1. To protect data lines and the power line, connect

pins 2 & 3 directly to the positive supply rail (VCC).

In this configuration the data lines are referenced

to the supply voltage. The internal TVS diode

prevents over-voltage on the supply rail.

2. The SRDA can be isolated from the power supply by

adding a series resistor between pins 2 & 3 and

VCC. A value of 10kW is recommended. The

internal TVS and steering diodes remain biased,

providing the advantage of lower capacitance.

3. In applications where no positive supply reference

is available, or complete supply isolation is desired,

the internal TVS may be used as the reference. In

this case, pins 2 & 3 are not connected. The

steering diodes will begin to conduct when the

voltage on the protected line exceeds the working

voltage of the TVS (plus one diode drop).

ESD Protection With RailClamps

Data Line and Power Supply Protection Using Vcc as

reference

Data Line Protection with Bias and Power Supply

Isolation Resistor

Data Line Protection Using Internal TVS Diode as

Reference

RailClamps are optimized for ESD protection using the

rail-to-rail topology. Along with good board layout,

these devices virtually eliminate the disadvantages of

using discrete components to implement this topology.

Consider the situation shown in Figure 1 where dis-

crete diodes or diode arrays are configured for rail-to-

rail protection on a high speed line. During positive

duration ESD events, the top diode will be forward

biased when the voltage on the protected line exceeds

the reference voltage plus the V

drop of the diode.

For negative events, the bottom diode will be biased

when the voltage exceeds the V

of the diode. At first

Applications Information

6ã 2000 Semtech Corp. www.semtech.com

PROTECTION PRODUCTS

SRDA3.3-4 THRU SRDA12-4

PIN Descriptions

Figure 1 - Rail-To-Rail Protection Topology

(First Approximation)

Figure 2 - The Effects of Parasitic Inductance When

Using Discrete Components to Implement Rail-To-Rail

Protection

Figure 3 - Rail-To-Rail Protection Using

RailClamp TVS Arrays

Applications Information (continued)

approximation, the clamping voltage due to the charac-

teristics of the protection diodes is given by:

= V

+ V

(for positive duration pulses)

= -V

(for negative duration pulses)

However, for fast rise time transient events, the

effects of parasitic inductance must also be consid-

ered as shown in Figure 2. Therefore, the actual

clamping voltage seen by the protected circuit will be:

= V

+ V

+ L

ESD

/dt (for positive duration pulses)

= -V

- L

ESD

/dt (for negative duration pulses)

ESD current reaches a peak amplitude of 30A in 1ns

for a level 4 ESD contact discharge per IEC 61000-4-2.

Therefore, the voltage overshoot due to 1nH of series

inductance is:

V = L

ESD

/dt = 1X10-9 (30 / 1X10-9) = 30V

Example:

Consider a V

= 5V, a typical V

of 30V (at 30A) for the

steering diode and a series trace inductance of 10nH.

The clamping voltage seen by the protected IC for a

positive 8kV (30A) ESD pulse will be:

= 5V + 30V + (10nH X 30V/nH) = 335V

This does not take into account that the ESD current is

directed into the supply rail, potentially damaging any

components that are attached to that rail. Also note

the high V

of the discrete diode. It is not uncommon

for the V

of discrete diodes to exceed the damage

threshold of the protected IC. This is due to the

relatively small junction area of typical discrete compo-

nents. It is also possible that the power dissipation

capability of the discrete diode will be exceeded, thus

destroying the device.

The RailClamp is designed to overcome the inherent

disadvantages of using discrete signal diodes for ESD

suppression. The RailClamps integrated TVS diode

helps to mitigate the effects of parasitic inductance in

the power supply connection. During an ESD event,

ã 2000 Semtech Corp. www.semtech.com

PROTECTION PRODUCTS

SRDA3.3-4 THRU SRDA12-4

Applications Information (continued)

the current will be directed through the integrated TVS

diode to ground. The total clamping voltage seen by

the protected IC due to this path will be:

= V

F(RailClamp)

+ V

TVS

This is given in the data sheet as the rated clamping

voltage of the device. For an SRDA05-4 the typical

clamping voltage is <16V at I

=30A. The diodes

internal to the RailClamp are low capacitance, fast

switching devices that are rated to handle high tran-

sient currents and maintain excellent forward voltage

characteristics.

Using the RailClamp does not negate the need for good

board layout. All other inductive paths must be consid-

ered. The connection between the positive supply and

the SRDA and from the ground plane to the SRDA

must be kept as short as possible. The path between

the SRDA and the protected line must also be mini-

mized. The protected lines should be routed directly to

the SRDA. Placement of the SRDA on the PC board is

also critical for effective ESD protection. The device

should be placed as close as possible to the input

connector. The reason for this is twofold. First,

inductance resists change in current flow. If a signifi-

cant inductance exists between the connector and the

TVS, the ESD current will be directed elsewhere (lower

resistance path) in the system. Second, the effects of

radiated emissions and transient coupling can cause

upset to other areas of the board even if there is no

direct path to the connector. By placing the TVS close

to the connector it will divert the ESD current immedi-

ately and absorb the ESD energy before it can be

coupled into nearby traces.

(Reference Semtech application note SI99-01 for

further information on board layout)

technology, the SRDA3.3-4 can effectively operate at

3.3V while maintaining excellent electrical characteris-

tics.

The IV characteristic curve of the EPD device is shown

in Figure 4. The device represents a high impedance

to the circuit up to the working voltage (VRWM). During a

transient event, the device will begin to conduct as it is

biased in the reverse direction. When the punch-

through voltage (VPT) is exceeded, the device enters a

low impedance state, diverting the transient current

away from the protected circuit. When the device is

conducting current, it will exhibit a slight snap-back or

negative resistance characteristic due to its structure.

This must be considered when connecting the device

to a power supply rail. To return to a non-conducting

state, the current through the device must fall below

the snap-back current (approximately < 50mA) to allow

it to travel back through the negative resistance

region. If this is a concern, a 10kW current limiting

resistor can be placed between the supply rail and the

positive reference pins (2 & 3) to prevent device latch-

up.

RailClamp is a registered trademark of Semtech corporation

5:0

%55

Figure 4 - EPD TVS IV Characteristic Curve

SRDA3.3-4 EPD TVS Characteristics

The internal TVS of the SRDA3.3-4 is constructed using

Semtechs proprietary EPD technology. The structure

of the EPD TVS is vastly different from the traditional

pn-junction devices that are internal to the SRDA05-4

and SRDA12-4 devices. At voltages below 5V, high

leakage current and junction capacitance render

conventional avalanche technology impractical for

most applications. However, by utilizing the EPD

8ã 2000 Semtech Corp. www.semtech.com

PROTECTION PRODUCTS

SRDA3.3-4 THRU SRDA12-4

T1/E1 Interface Protection

Universal Serial Bus ESD Protection

Typical Applications

ã 2000 Semtech Corp. www.semtech.com

PROTECTION PRODUCTS

SRDA3.3-4 THRU SRDA12-4

Land Pattern - SO-8

Notes:

(1) Controlling dimension: Inch (unless otherwise specified).

Outline Drawing - SO-8

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PROTECTION PRODUCTS

SRDA3.3-4 THRU SRDA12-4

Contact Information

Semtech Corporation

Protection Products Division

652 Mitchell Rd., Newbury Park, CA 91320

Phone: (805)498-2111 FAX (805)498-3804

Ordering Information

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ET.4-50ADRSV50052hcnI31

BT.4-21ADRSV21005hcnI7

ET.4-21ADRSV210052hcnI31

Note:

(1) No suffix indicates tube pack.