简单看了一下datasheet

 Channel A's conversionresult is outputted on DOUTA while Channel B's conversion re-sult is outputted on DOUTB.

貌似是2路输入输出，你确定你输入了2路被测信号？

还有建议看看第8个管脚DUAL，sheet上有这么一段说明：Applying a logic high to this pin causes the conversion result of Channel A to be outputon DOUTA and the conversion result of Channel B to be output on DOUTB. Grounding thispin causes the conversion result of Channel A and B to be output on DOUTA, with the resultof Channel A being output first. DOUTB is in a high impedance state when DUAL isgrounded.

大致意思是这个管脚的电平状态会影响输出位置。拉高，A路输入转换后从OUTA输出，B路输入转换后从OUTB输出；拉低，AB输入转换后都从OUTA输出，A先输出，B再输出，这个时候OUTB端高阻。

理论上TTL工艺IC的管脚悬空默认为高电平，但是实际上有很多不可预计的问题。

以上仅供参考。