Whilst torture-testing a design that is largely based on the i.MX28 EVK, we are encountering intermittent soft reboot/reset failures. The behavior is the same as that observed earlier during the design process when we discovered that we were exceeding the 100mA inrush current limitation imposed by the power supply subsystem (i.MX28 Applications Processor Reference Manual, Rev.2 p. 947). This prevents the startup sequence from completing, and leaves the board in a totally locked up state.
The occurrence is very rare, but because of the nature of the product, this type of behavior is simply not something we can ship with.
We believe we have traced the root cause to the DDR2 memory, which is powered from the VDDA rail. We are using a 256MB part: Micron Technology, Inc. - MT47H128M16RT-25E
Using a current probe, upon reset we see the inrush hitting a 100mA ceiling. Driving the DDR2 from a separate rail lowers that current to around 60mA. This isn't a suitable solution because it prevents us from being able to operate under battery power.
We are seeking a recommendation on how to resolve this. For example, any suggestions for alternative 256MB DDR2 parts that operate within the 100mA constraints. We are approaching the end of the development cycle, so we really have to implement the least invasive fix possible.
Thanks in advance,