I have a issue with function pins of AD9914. I do not have enough pin to drive AD9914 all control pins. Therefore, I decided to use I/O expander. In this condition, I select Texas Instruments PCF8575PW I/O Expander. Theoretically, I do not have a issue with control pins of AD9914 but in real life condition I saw that I/O expander can not be achieve to drive function pins of AD9914. When I try to set these pins High, I saw that I/O expander can only give 2 V , however ,without function pins connection, I/O expander voltage on these pins are 3.3V (as expected).
As a result, there can be problem with I/O expander and AD9914 function pins because other pins of AD9914 is driven by I/O Expander. Could you please help me figure out the problem?