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LTC3639 Maximum Input Voltage


We are using the LTC3639 part in a power supply circuit which takes a input voltage that varies between 65 and 110VDC and outputs 5VDC. We want to protect the input pin from high voltage transients however we don't know what voltage this device needs to be protected to. The datasheet for the part says that the "Absolute Maximum" Supply voltage is 150VDC, however it is suggested that the device will work just fine at 150V i.e. there is no distinction between the "recommended" operating voltage range and the "Absolute Maximum"

When selecting a TVS diode a usual rule of thumb for specifying the diode is to set the breakdown voltage at 20% above the maximum expected operating voltage and ensure the maximum clamping voltage is below the maximum rating of the pin. In our case if we follow these criteria we need a diode with a breakdown voltage at or greater than 132V and assuming the device will be damaged when above 150V the maximum clamping voltage should be 150V or lower. A TVS diode or similar transient protection device with such a narrow tolerance does not seem to be available on the market.

What is the maximum transient voltage the device can sustain before being damaged and do you have any guidance for selecting protection components for this device?