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TLV7042: Input Pin Overvoltage Protections

Grayson Capers
Prodigy 20 points
Part Number: TLV7042
Other Parts Discussed in Thread: TLV3402

Hello,

I have a question regarding the TLV7042. I have the two TLV7042 comparators acting as a window comparator. Vx (labeled on the schematic below) can have a voltage from 0-12V. In order to protect the input of the window comparator when Vx reaches above the absolute maximum input rating of the comparators, R39-3 and D5-3 were added to "clamp" Vin to 4.7V in such an event. However, D5-3 has enough reverse leakage current that Vin is pulled below the 4V window comparator threshold even when Vx is ~5V.

Long story short, I am wondering if the inputs to the TLV7042 would still be protected if I removed D5-3 and kept R39-3? The datasheet mentions the input terminals are "diode-clamped to VEE", but does not mention any diode clamping to VCC. Are there any internal protections here that would allow me to simply remove D5-3, or will I have to find a less-leaky diode?

Thanks,

Grayson Capers

  • 0
    TI__Mastermind 23970 points

    Grayson

    thanks for your post Grayson and your concerns are valid.  As you pointed to, our device does not have the traditional input diode clamping diode to VCC.  As a result, we are able to tolerate voltages up to our process max without damaging the input or causing the input bias current to increase.  The input ESD diode protection which is not designed to protect against DC voltages looks something like this where the snapback voltage occurs in the 10 to 12V range.  You can not rely on this structured to be your protection against the 12V you mentioned in your circuit.  So you will need to find a less leaky diode or consider switching to a device such as the TLV3402.  If you used this device, I would be comfortable saying that I would not expect an issue with your signal going to 12V.  So this solution would allow you to eliminate the external diode from your circuit.  Only drawback is that we don't offer the DDF package for the TLV3402 yet but we will in the future.  Sorry, I realize this probably is not the response you were hoping for.

    Chuck