MSP430FR6047: MSP430FR6047 design help

Part Number: MSP430FR6047

Hi team,

I got a question from custom:

We are trying to make watermeter with MSP430FR6047 and working with USS GUI. Because we have such a short distance between two transducer(about 4cm). I need to set a [Gap between pulse start and ADC capture(us)] parameter around 20us. Although the document state the minimum parameter value as 3us, ADC capture display stop working when it goes down to 26us. Please let me know why is this happening.

Please provide a reference answer.thanks

Best regards,