Puzzling behaviour od AD5336

Question

Hi Guys, 
 I'm driving an AD5336 and my test code steps from 0 to 1023, then repeats until I stop it. 
 The chip has a 3V3 supply and all of the Vref pins are at 3V0. LDAC and GAIN are both 0V and PD is at 3V3. Outputs are presently not disconnected to preclude any external influence. 
 The puzzle is that, rather than rising 0V to 3V0 over the count as I expect, it ramps from 0V to 2V5 over the data range 0..~350, then stops rising. 
 I can see all the data changing as I expect and even if I had bits swapped or stuck, I would not see the steady ramp to 2V5. 
 I've replaced the chip, but still get the same behaviour. 
 Can anyone shed any light on this, please? 
 Thanks. 
 Message was edited by: Gordon Scott (correction .. strikeout of inadvertant 'not')

GordonS · Accepted Answer

I think I've seen the problem. 
 My schematic shows p15 as power, duplicating PDs pin number. I think this chip has no power. 
 I'm trying that now. 
 Oh good grief! Yes it is! I don't know how many times I've checked that and not seen it. 
 Works fine now. 
 Message was edited by: Gordon Scott adding conclusion.