Tool/software:
Hi I've got a design with two instances of TPS63901 buck boost converter. One is 5 to 3.6V and the other is 5 to 5V. (The input 5V can go down to 2.5V so that's why the application uses buck boost). For both circuits, on all the boards in the proto run I've tested it seems the output is still active even with EN=0. It seems pretty straightforward that a low on enable should cut the output but on the 5-3.6V circuit I'm still measuring switching on LX1 and the output is stable at 3.6V prob with a very light load. (3.6V more interesting to discuss the rest of this post since it's the part is switching whereas the 5 to 5V is just in passthrough and the same thing must be happening to both circuits). The 3.6V is going to one load on the board and I'm not seeing anything else that could be putting 3.6V onto the net but I'm not really able to disconnect the reg output from the rest of the board.
What am I missing.. why is TPS63901 switching even with enab low ?
I'm attaching a pic of the layout with enable highlighted. I'm probing EN on that TP and I don't see any other possible driving source. I suppose it's possible that the enable ball didn't get soldered to the pad but every instance of this circuit across a handful of boards we've tested do the same thing so I don't think that is likely.
Config for the 3.6V circuit:
L = 2.2u, CIN, COUT nom per rec
SEL = 10k to gnd. EN driven by p/p IO measured to be 0V by dmm and scope by two people
CFG3 = 20.2k to gnd; CFG2 = 8.25k to gnd; CFG3 = 1.15k to gnd
Probe LX1 looks consistent with buck in dcm:
Thanks,
