Yes, I know that the Semtech datasheet is unipolar. That's why I asked on what could be done for negative transient clamping?Above linked Semtech TVS arrays are unipolar, as clearly indicated by the schematic. Negative clamping voltage is silicon diode forward voltage, unfortunately not further specified in the datasheet.
Yes. In the given datasheet the knee voltages are different.the clamping is symetrical (assuming the knee voltages are the same)
Hi,
As the datasheet shows there are two anti series zeners inside.
Thus in one direction the voltage is limited by 15V zener and in the other direction by the 24V zener.
Pin1 is the cathode of the 15V zener, pin2 is the cathode of the 24V zener.
Now it depends how you decide your test setup.
1)
In one test they connected pin1 to GND and get a positive limit at around +24V.
In the other test they connect pin2 to GND and get a limit of about +15V.
(Upper diagrams of fig 5)
2)
In one test they connected pin1 to GND and get a negative limit at around -15V.
In the other test they connect pin2 to GND and get a limit of about -24V.
(Lowrr diagrams of fig 5)
3)
You could also decide to always connect with pin1 = GND and get limits at +24V and -15V (positive and negative)
4)
You could also decide to always connect with pin2 = GND and get limits at +15V and -24V (positive and negative)
All 4 methods are redundant to each other and should give identical results
I'd say it's a rather uncommon protection part with asymmetrical limits. But the datasheet is clear.
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So if you want to limit at -0.5V ... this (single) part is not suitable.
You may use it ... but use a parallel schottky diode.
You may use a single part with limits according your application.
*******
Btw: some ICs define their limit by "VCC + 0.6V" for example.
Mind that a protection device with 5.0V limit only protects if the IC is properly powered with at least 4.4V.
If the IC is not powered at all (switched off, Vcc = 0V) or VCC is less than 4.4V then the protection is not guaranteed.
Klaus
Completely wrong. Do you read the answers in your thread? As stated, the Semtech device protects perfectly against negative transients, but doesn't allow negative signal greater than diode forward voltage. If (and only if) your application requires negative signal swing, you'll choose a bipolar TVS device.1. So, if I use the Semtech part in my application, it is a unipolar device and used for only protection against positive transients and not negative transients, right?
Thank you.Hi,
1)
I don't know how I could write it more clearly: it limits 15V in one direction and 24V in the other.
So for sure it limits both ways. Negative as well as positive.
2)
If ... if the device allowes "VCC + 0.6V" maximum voltage ... and now if not powered, then VCC = 0V.
Then obviously "VCC + 0.6V" = "0V + 0.6V" = 0.6V.
--> you must not apply more than 0.6V to the IC's input. This can not be fulfilled with the above protection device. No protection.
Klaus
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