BQ2973: The Dout is always low

Part Number:BQ2973

Dear sir

I use the BQ2973 for the battery protection. Here is the schematic.

I used a DC power supply to add a 4V between BAT+ and BAT-. I found the CSD87313 is not on. I measued the Cout and Dout of BQ2973, Cout = 1 and Dout =0? 

Why this is happened? 

Thanks

BR 

Ren