Hello Guys,
I'm now using BUF20800 to drive an LCD as Gamma generator. I found an odd question here. I power up the IC by 18V and generate REFH 17.8V and REFL 0.2V by simple power-divider as shown in typical application circuit. The IC works fine in general. However, whenever I wish 17.5V of the output 14 and send the data to the IC, I get 17.9V, which is the actual value of Vs and even more than the pre-set REFH.
First I try different value from 17.0 to 17.5 and find out that by sending data less than 17.4V the output can give desired value, but more than 17.4 the output voltage becomes more than REFH.
Secondly, I try to make all output channel to be 17.5 and the results show that from Ch1 to Ch9 the output are correctly 17.5, but from Ch10 to Ch18 the output are more than REFH.
Thirdly I check the data sent to the IC by logic analyser and it shows the data is 03F0, which is 1008 in dec. By using the output voltage formula, Vout = [(17.8-0.2)/1024 * 1008] + 0.2 =17.525, which means the data is also correctly sent to IC.
Do someone has similar problem with me? Can someone help me to explain why the output can exceed the REFH?
Kind regards,
Zhen
