XM3 and HM3 built-in thermistor Isolation Voltage

Shige

Hello,

According to datasheet, case to terminal isolation voltage is 4kVac.

How about built-in thermistor? Can I use a thermistor without isolation ?

Best regards,

Forum_Moderator

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svinueza_2018

Hi Shige,

The isolation voltage between the thermistor and all the other terminals matches the 4 kV at 50 Hz for 1 min rating, and was verified during module validation.

It is not recommended to operate the thermistor without additional isolation, but it is functional during normal operation.  If a failure occurs, a path can be formed between the NTC and a high voltage node inside the module due to wirebonds shifting position during a catastrophic event. The isolation of the internal NTC thermistor only qualifies for functional isolation, which is not guaranteed to be maintained during failure.  Assuming reinforced isolation is required, it can be added externally as follows:

• Using analog amplifiers with enclosed isolation to sense the voltage across the NTC.
• Using a digital isolator to transfer the encoded NTC voltage to the controller.  An example of this method can be found in reference design gate driver here: CGD1700HB2P-XM3
  https://www.wolfspeed.com/cgd1700hb2p-xm3/

Thanks,

TBhatia

Hi, I hope that this answered your question. I will close this discussion for now but if you have a follow up question, please "Start a New Discussion" and we would be glad to support you further.