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UCC21521: Primary-Side logic failure meaning

Marco Rojas
Intellectual 2780 points
Part Number: UCC21521

Tool/software:

Hi team,

I have a customer with the below question on the UCC21521. Let me know what you think and thanks in advance!

"I had a question about a UCC21521 Isolated Gate driver. In the datasheet, on the first page it states that 'As a fail-safe measure, primary-side logic failures force both outputs low'. 

I could not find any documentation on what constitutes a 'primary-side logic failure'. Is there anyway you can help me determine what a 'primary-side logic failure' is?"

Marco

  • 0
    TI__Mastermind 23196 points

    Hi Marco,

    Essentially, this just describes the way an isolated gate driver works. It is a multi-chip module, with both an input die (primary side logic) and an output die (with large transistors that supply Igate). Alternatively these are called the TX die and the RX die, because the input die will send a 515MHz on-off keying frequency across the isolation capacitor when it receives an input "high". The output side receives this 515MHz signal, and enables the pull-up network to drive the output "High". When the input die receives an input "low", it sends no signal to the output die, and both outputs will remain low. Therefore, if the input die is destroyed or otherwised disabled, no 515MHz will be transmitted, and the outputs will simply remain low; there is no danger that the driven FETs will turn on if the input side is damaged.

    Best regards,

    Sean