# LTC6957-x VINSE vs. VINDIFF Clarification

Hi,

I understand the maximum value for the peak-peak single ended signal (VINSE) that can be applied to LTC6957-x input is 2V pk-pk from below datasheet snapshot. This might for example be in a case where the IN- pin is AC coupled to GND and the IN+ pin is driven with an AC coupled 2V pk-pk sine wave.

If this is the case, I don't see how the maximum value for the peak-peak differential signal that can be applied to the LTC6957-x input is also 2V pk-pk. I would expect it would be double this value. This might apply to a case where a differential signal is applied to the IN+ and IN- pins of the LTC6957 as is shown in the below image. Referring to the image below, which of the two figures represent what is mean by VINDIFF in the LTC6957 datasheet? If it's figure 3, I might argue the VINDIFF value should be listed in the datasheet as double what it currently is. If it's figure 4, I would be interested to understand how that could be the case considering the VINSE is 2Vpk-pk which would imply to me the LTC6957 can only handle half the voltage difference between IN+ and IN- when driven differentially that it can when driven single-ended.

Thanks.

Parents
• Hello,

The 2Vpp limit is determined by the back to back diodes between the IN+/IN- inputs (figure 1 in datasheet).  The 2Vpp limit applies to either the SE or differential case as a result.

What happens is IN+ approaches 1V above(or below) IN-, the back to back diodes begin to turn on.  This then starts to clip the input signal and also sends some current through these diodes.  The overall performance begins to degrade as result.

• Actually one followup question.

Can ADI provide any information that describes or quantifies the extent to which performance would be degraded for VPP greater than 2V?

• Sorry, we can not provide this.  Results would vary depending on process, votlage and temperature,  Also in the absolute maximum table on page 2 of the datasheet it states not to exceed +/-10mA input current on the IN+/- pins.  This happens when those back to back diodes turn on.  This will become a quality problem at some point above the 2Vpp limit.