ZedBoard and MicroZed both use DDR3L because that is the memory that is most readily available from Micron. The DDR3L is fully backward compatible with DDR3 when the DDR3L is operated at 1.5V. (See Micron document TN-41-14: DDR3 SDRAM 1.35V-to-1.5V Compatibility Introduction)
At the time ZedBoard and MicroZed were designed, Xilinx did not support operating Vcco_ddr at 1.35V. In the datasheet now, you will see that Vcco_ddr has recommended operating conditions at both 1.5V and 1.35V.
ZedBoard and MicroZed both use DDR3L because that is the memory that is most readily available from Micron. The DDR3L is fully backward compatible with DDR3 when the DDR3L is operated at 1.5V. (See Micron document TN-41-14: DDR3 SDRAM 1.35V-to-1.5V Compatibility Introduction)
At the time ZedBoard and MicroZed were designed, Xilinx did not support operating Vcco_ddr at 1.35V. In the datasheet now, you will see that Vcco_ddr has recommended operating conditions at both 1.5V and 1.35V.
