I'm evaluating a first article PCB from a new-ish supplier to us. The board doesn't get to the point of booting the Linux kernel, but it does get through the first few seconds of booting to an SD card, so a bunch of stuff must be working. The debug messages complains "smps8: failed to apply 1800000uV constraint(-22)" followed by these:
[ 0.461407] palmas-pmic 48070000.i2c:tps659038@58:tps659038_pmic: failed to register 48070000.i2c:tps659038@58:tps659038_pmic regulator
[ 0.462072] palmas-pmic: probe of 48070000.i2c:tps659038@58:tps659038_pmic failed with error -22
So I've been probing around the PMIC, and stumbled into finding the 1.8V is only about 1.69V, which is below the 1.71V lower limit. The signal on the PMIC side of the inductor is really erratic, suggesting to me that it's struggling to put out enough current. I have good versions of this board from another CM, and the PMIC output on this one looks solid.
The processor on New CM's 1st article also gets a little warmer than the current CM. So I concluded that something is sucking extra 1.8V.
Are there versions of am5728 that consume more current on the 1.8V rail than version 2.0? Is there a potential sneak circuit here that's pulling juice from 1.8V?
Just for fun, here are scope shots. First one is from the new CM's board, second is from current CM's board.
Any thoughts from the forum would be welcome.
BR
Mike
