i designed the PCM1681 circuit followed by the datasheet, and  sclk bck lrck datain1-4 are all came

 from a fpga . but once i input the sclk in the pcm1681's 5 pin(sclk)(the other input pins are float) , the dataout 1-8 are all output shaped wave between the 2.5V voltage. and the shape is like the Square wave .    when i input the bck ,lrck and datain1-4  , the output is ok except the Square wave is still there.

i don't know why this happen,  have u see this before?  thx a lot!.