SN74LVC1G125: how to test the lack of ESD clamping diode @ VCC

Yohann YVENOU

Part Number: SN74LVC1G125

Tool/software:

I often see in discussions that when people test the presence or not of the ESD protection diode on a chip, they source 100µA @ vcc=0V with a clamp=2V.

No problem for me if absolute maximum rating grant I/O be above VCC (for SN74LVC1G125 it is ok in the respect of 6.5V).

But what if absolute maximum rating forbide I/O be above vcc+0.7V for example:

- Can we source 100µA with clamp 2V?

- Can we say "there is no much current so we can go to 2V when there is no ESD protection diode" ?

If we can't do that, how can you test the lack of ESD protection diode without going above vcc +0.7V?

2 months ago

0 Clemens Ladisch 2 months ago

Guru 294990 points

When there is a diode, the absolute maximum ratings usually say that "the input voltage ratings may be exceeded if the input current ratings are observed" (and there is a current rating).

If there is no current rating for positive voltages, then the absolute maximum ratings usually are independent from the supply voltage, and you know that there is no diode.

(See [FAQ] Can the input voltage (Vi) to my logic device be higher than the supply voltage (Vcc)?)

If there is no current rating for positive voltages,and the absolute maximum ratings forbid voltages above V_CC + 0.5 V, then you do not know from the datasheet. While strictly speaking not allowed, you can do the test with a sufficiently low current limit; 0.1 mA is fine.

Please note that in the last case, whether there is a diode or not does not matter because your circuit is not allowed to rely on this fact.

0 Yohann YVENOU 2 months ago in reply to Clemens Ladisch

Prodigy 50 points

Thank you Clemens, .... but "sufficiently low current limit; 0.1 mA" is from a personal experience? Or is there any document which tells it is a good value 0.1mA with a clamp @ 2V?

0 Clemens Ladisch 2 months ago in reply to Yohann YVENOU

Guru 294990 points

I estimate that a power dissipation of less than 100 µW in the diode is harmless.

0 Yohann YVENOU 2 months ago in reply to Clemens Ladisch

Prodigy 50 points

Ok but I meant using 0.1 mA with clamping at 2V for testing pin without diode @ Vcc=0V, is there something which tell us it's safe (even if absolute maximum rating tells not going above vcc+0,5V) ?

+1 Clemens Ladisch 2 months ago in reply to Yohann YVENOU

Guru 294990 points

When there is no diode, then no current flows as long as the gate isolation does not break down. It would be rated for at least the maximum supply voltage.

0 Yohann YVENOU 2 months ago in reply to Clemens Ladisch

Prodigy 50 points

Thank you very much Clemens, it's clear :)

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SN74LVC1G125: how to test the lack of ESD clamping diode @ VCC