AD7476A LSB offset


i am using three AD7476A ADCs in the design. All three of them have a constant offset of about 35 LSB.  I expect an Offset of max 2-4 LSB. Can someone explain why?

VCC is 3,3VDC. Vin is for example 1,7VDC with expected 2111 LSB at 3,3V-4096  (Acutal measured value is 2076). All parts are driven via TTL 3,3V Level. CLK = 5MHz.

Even at varying Vin values all three ADCS have a constant Offset of About 35 LSB.

Best Regards,