SL05T1 Series

http://onsemi.com

4

Applications Background

This new family of TVS devices (SL05T1 series) are

designed

to

protect

sensitive

electronics

such

as

communications

systems,

computers,

and

computer

peripherals against damage due to ESD conditions or

transient voltage conditions. Because of their low

capacitance value (less than 5 pF), they can be used in high

speed I/O data lines. Low capacitance is achieved by

integrating a compensating diode in series with the TVS

which is basically based in the below theoretical principle:

The Figure 5 shows the integrated solution of the SL05T1

series device:

Figure 5.

COMPENSATING

DIODE

TVS

In the case that an over−voltage condition occurs in the I/O

line protected by the SL05T1 series device, the TVS is

reversed−biased

while

the

compensation

diode

is

forward−biased so the resulting current due to the transient

voltage is drained to ground.

If protection in both polarities is required, an additional

device is connected in inverse−parallel with reference to the

first one, the Figure 6 illustrates the inverse−parallel

connection for bi−directional or unidirectional lines:

Figure 6.

3

2

1

3

2

1

An alternative solution to protect unidirectional lines, is to

connect a fast switching steering diode in parallel with the

SL05T1 series device. When the steering diode is

forward−biased, the TVS will avalanche and conduct in

reverse direction. It is important to note that by adding a

steering diode, the effective capacitance in the circuit will be

increased, therefore the impact of adding a steering diode

must be taken in consideration to establish whether the

incremental capacitance will affect the circuit functionality

or not. The Figure 7 shows the connection between the

steering diode and the SL05T1 series device:

Figure 7.

STEERING DIODE

SL05T1 DEVICE

Another typical application in which the SL05T1 series

device can be utilized, is to protect multiple I/O lines. The

protection in each of the I/O lines is achieved by connecting

two devices in inverse−parallel. The Figure 8 illustrates how

multiple I/O line protection is achieved:

Figure 8.

OUTPUT

INPUT

For optimizing the protection, it is recommended to use ground planes and short path lengths to minimize the PCB’s ground inductance.