AN1826 - APPLICATION NOTE

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than the Varistor to clamp and to derivate surge energy. Turn-on time measured on a Transil is typically

below the 10 picosecond level, while a Varistor will be in the range of 500 to 1000 ps at the best. In the first

few ns, the parasitic inductance and reaction time generate >70V peak for the Varistor while this value is

limited to 55V only for the Transil™. After this phase, the maximum voltage is 30V for the Varistor while we

Another point to take into account is the system reliability. So ensuring device reliability and avoiding

ageing phenomena are two major concerns. To check these two points, repetitive ESD tests have been

performed (100 pulses versus IEC61000-4-2 system standard 15kV contact).

Fig. 6: Varistor and Transil™ repetitive ESD test results.

Varistor

-200

-150

-100

-50

0

50

100

150

200

-20

-10

0

10

20

Voltage (V)

Before

After

Transil

TM

-200

-150

-100

-50

0

50

100

150

200

-20

-15

-10

-5

0

5

Voltage (V)

Before

after

remains the same. This phenomena is called ageing . So the integrity of the protected system will be

greatly dependent on the choice of the protection component.

Transil™ diode technology can be easily used in more complex integration where dedicated ESD

protection is required and space saving is a major concern. For instance this is particularly true in computer

and mobile phone applications. This is the case for USB link, which is based on plug and play connection.

This kind of surges is always omnipresent.

which integrates either the ESD protections, the line matching resistors (Rt), the filtering capacitors (Ct)

and the pull down resistors. All this internal component are required by the USB standard.

Varistor

Transil™

Leakage current

--

++

ESD ruggedness

+++

+++

Protection efficiency

--

++

-++

Ageing

---

+++

Security

--

+++

Table 2: Comparison sum-up.

D+ In

D- In

Gnd

D+ Out

D- Out

Rt

15k

Ct

Rt

Ct

15k

Fig. 7: USBDF01W5 circuit.