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TPS51116 VDDQ Set to 1.8V but Creeping higher to >1.9V

Mark Keisling
Prodigy 20 points
Other Parts Discussed in Thread: TPS51116

We have a design using the TPS51116 to power our DDR2 SODIMM module.  We're using the TPS51116 in DCAP mode at 1.8V.  Most of the time the design works but we are getting units back in which VDDQ is creeping up to values greater than 1.9V which eventually causes read/write failures to the DDR2.  The processor runs off of a separate 1.8V supply.

Any ideas on what to look at would be appreciated.  S3, S5, MODE, COMP, and VDDQSET are all tied to V5IN. CS is tied to V5IN with a 5.11K resistor.  We're using SI4442DY FETs with 5 milliohm turn on resistance.  Output is filtered with 4 68 uF 0.06 ohm ESR electrolytic caps.

Thanks,

Mark Keisling