I'm thinking about using a 64A4 in a new design and have been evaluating 3.3V linear regulators since I'd prefer to run off a single 5V supply for the rest of the system. All the ones I've found have claimed sensitivity to ESR on the output cap, but even using allegedly compliant caps doesn't seem to eliminate unacceptable spikes (up to 4.1V) when switching 200 mA (the max. the part is supposed to consume).
Has anyone else dealt with this issue? What solution did you come up with? Thanks.
Insert a resistor between the regulator output and the output cap so ESR is guaranteed within range. Maybe you need a little more input/output capacitance, and maybe the layout is not optimal.
The output cap "issue" is inherent in low dropout regulators. And, that is what you need to get 3.3V out from 5.0V in.
I would not try to to handle a switched maximum load. The transients will eat your circuit alive.
Consider what you have with 200ma load, switched, or not. Voltage_drop = Vin - Vout = 1;7V. Power is voltage_drop * Current = 0.34W. I am willing to bet that this is far greater than your regulator can handle without substantial heat sink, and maybe not at all if its one of those nice little SOT23-5 packages.
What LDO are you trying to use?
Jim
