DAC8551: output oscillation from DAC

chip has "TI 82    D81" marking on the surface. 

I have tried removing A8 cap, disconnected Vctrl_0 that goes to an OPAMP.  Still get oscillation. 

I am seeing same problem with Vdd=5V, Vref=2.5v also. 

This is the output I get. Very strange. 

I am updating the DAC 4 times a second, the line should be flat, not sure why I am getting the high freq.  I thought it is cap load so I removed all the caps on the Vref and even disconnect the output to OPAMP, but problem persist. 

Hi Andrew,

Can you confirm that your input voltages (reference and VDD) are stable? An oscillating input voltage can cause oscillation on the output.

Thanks,
Erin

Yes, I have verified with my scope, that Vdd and Vref are good. This ringing / oscillation is quite high, Vpp is 1V. Freq is very high as well 3Mhz. 

I removed the 20K resistor and the oscillation went away. Maybe stability issue? 

datasheet looks fine with 20K to increase the gain.