ISO1212: use of the component in certified STO system

Fabio Vitali

Part Number: ISO1212
Other Parts Discussed in Thread: ISO1211

HI. I used the component in the STO (safe torque off) circuit.

I am in the process of product certification and need to know if the ISO1212 component has a common point of failure between channels, i.e. that an internal failure on one channel can lead to a failure in the other.
Do you have data or information about it?

Do you think that to achieve SIL3 you must necessarily use an independent single channel device (like ISO1211)?

Thanks for your help

Fabio

over 1 year ago

0 Andrew J over 1 year ago

TI__Mastermind 26765 points

Hello Fabio,

Thanks for reaching out.

ISO1212 has functional isolation in between the inputs up to +/-60V in between isolation. This means that if one is input is damaged the other should still operate. The only reason for a single channel failure to spread to the other input channel is if safety-limiting values are not maintained (see 6.8 Safety Limiting Values).

In most cases damage to an input is caused by a transient or overstress event that lasts only a few microseconds. In this case, one input would be damaged, and the remaining input and output die (and isolation barrier) are maintained.

However, secondary damage may occur to the other parts of the device if the fault condition stays and heats the device past the maximum junction temperature (150degC). Adhering to the safety-limiting values can prevent the device from heating up and help maintain the isolation barrier and functional isolation between channels.

Documentation on safety limiting values is available on our FAQ page. I have linked the articles related to safety-limiting values and failure modes below for your convenience:

Hopefully this helps.

Best,
Andrew

0 Fabio Vitali over 1 year ago in reply to Andrew J

Prodigy 10 points

Hi Andrea.
Thanks for the quick and clear response.
I have one more question.
What common failure is possible in the secondary part of the ISO1212 component (even without failure in the primary parts)?
Is it possible that, in the event of component failure, both outputs take on the same value, for example VCC?
This is my last doubt to analyze the safety of the component in the STO circuit and proceed with the certification, without remake the board with the single channel version of ISO1211.
Thank you very much for your collaboration and expertise.
Have a nice day

Fabio

+1 Andrew J over 1 year ago in reply to Fabio Vitali

TI__Mastermind 26765 points

Hi Fabio,

Fabio Vitali said:
What common failure is possible in the secondary part of the ISO1212 component (even without failure in the primary parts)?
Is it possible that, in the event of component failure, both outputs take on the same value, for example VCC?

Like many other logic outputs, the output side of the ISO1212 does not have a defined failure mode. The output pins are standard CMOS outputs. If the absolute maximum conditions are exceeded, the output can fail randomly (either logic high or low).

Best,
Andrew

0 Fabio Vitali over 1 year ago in reply to Andrew J

Prodigy 10 points

Hi Andrew,

My last question: Does the ISO1212 component have a HFT (hardware fault tolerance) value? If yes, is it 0 or 1?

Thanks and good day

Fabio

0 Andrew J over 1 year ago in reply to Fabio Vitali

TI__Mastermind 26765 points

Hi Fabio,

If the input circuitry is damaged or not powered the outputs will be low or '0' by default.

Best,
Andrew

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ISO1212: use of the component in certified STO system