correct me if I am wrong but will
connecting the reference voltage to a analog pin directly be able to give out enough current?
Also VDAC will have its own errors
we want to use a circuit which can give a stable reference voltage without opamp buffer as we are going to use all the 4 available opamps of PSoC 5 LP
I note your goal : save the 4 Opamp.
Do you want use the PSoC also to generate a voltage reference?
May be be you need to add external Opamp in this case
all these parameters depends of your design : could you share a part of your design? It could be easier for us to help you.
You have some notes into the Cypress document about the Vref option for ADC, it depends also of the Clock frequency for your ADC.