Hello,
I wanted to report an issue that I've encountered with the Microzed board, in hopes that it can be improved in future revisions or that it can save others some time. I believe this is a bug in the hardware design, but please let me know if I've misunderstood something. I'm using Rev F of the board.
The 1.8V switcher is enabled by the power good (PG) output of the 1.0V switcher. The PG pin is open-collector, so it must be pulled up. This is done by R42, which pulls up to 1.0V, with R88 as a pull down making a voltage divider. The nominal value of PG_1V_10 when high is 1V*5k/(1k+5k) = 830mV.
This net drives the EN pin of U15. The datasheet for TLV62130RGT (http://www.ti.com/lit/ds/symlink/tlv62130.pdf) states that the minimum "high" input voltage for this pin is 0.9V, so the microzed is not meeting it. It works most of the time, but while debugging some intermittent problems with a USB device, we found that the 1.8V switcher was occasionally kicking off and collapsing for a short period of time (but long enough to cause problems communicating with the USB phy). We definitely had one board that had more problems than others, so there is also some board-to-board variance.
We've worked around this problem by blue-wiring the pullup to our 5V input voltage. I would suggest that microzed designers do the same in future revisions, perhaps with a zener to prevent the net from rising above the 7V max allowable voltage in the case where a higher input voltage is used to power the board.
