iCE40 LP/HX: Is there a list of a recommended diode for VPP_2V5 voltage like the one on many iCE40 eval boards?
The main purpose of this diode is to drive the 3.3 V supply down to a voltage within the datasheet requirements for the VPP_2V5 pin during NVCM programming. From page 19 of our document FPGA-DS-02029-3.5, this is stated to be a minimum of 2.30 V to a maximum of 3.00 V.
We do not have a list of recommended diodes, but its purpose is simply to be a cheaper alternative than having a separate LDO (2.3 V to 3.0 V output). CDBU0520 on some of our eval boards has a forward voltage of about 0.47 V on certain temperatures, which reduces 3.3 V to about 2.83 V. Do note that the maximum voltage limitation of 3.0 V on VPP_2V5 is during NVCM programming only. Normal operation (configuration and user mode) can go from 2.30 V to 3.46 V.