AM2432: Power Tree Questions

Hi Mari,

First, a couple of slight corrections:

• The VDD_1V8 rail is rated for 0.3A, not 3A
• The 9 rails split from VDD_1V8 are each rated for 0.05A, not 0.5A.

However, this doesn't actually change your point, as 9 * 0.05A is 0.45A, which is still greater than 0.3A that the rail is rated for.

The answer is that the ratings listed in the Power Tree is the maximum allowed current for each rail individually, and does not imply any ratings for the combination of the rails.  I.e. just because each of the rails that split off of VDD_1V8 each allow a max of 0.05A, doesn't mean that you should load each of these rails with 0.05A at the same time, as that would pull more than the 0.3A allowed out of the LDO.

In a typical usecase, each of the rails split off of VDD_1V8 will pull far less than 0.05A each, making the total draw on VDD_1V8 less than 0.3A.  In this case, if you want to put more load on some of the rails individually, as long as you keep the total draw on those rails below 0.05A AND the total draw on VDD_1V8 below 0.3A, then there are no concerns.

Let me know if that helps clarify this image and what it is trying to say.

Thanks,
Mike