Thanks for your comments and suggestions,actually it was not for defense but private industry also my company was working as a design service provider. In fact the path PWM solution went on to use when the manufacturer sourced displays from different vendors and the LED back lit current varied a lot.
I agree, for a product a short time software patch may be used, but if there is really a hardware design problem, sooner it is rectified the better.
Funny thing though, sometimes in the defense industry it is cheaper to change hardware than software anytime you are working with critical systems. As it turns out the work necessary to re-certify system safety software takes a lot longer and costs a lot more money than to re-certify the hardware changes.
We all like to get Brownie points for fixing problems like this. Ultimately, though, this is only a Band-Aid. It fixes one manifestation of shoddy layout & analog design (perhaps even provably, though probably only empirically). But what when the next batch of LDOs actually oscillate rather than just fall out of regulation? Let's not send the message that it's OK to forget about how to do good hardware design because some smart software guy can always fix it up!
It is always a software problem. Why? It is often easier to change software than anything else.
I've fixed many electronic and even mechanical defects in software. The oddest, perhaps, was fixing a lubrication defect in software.
The wrong lubricant was used to lubricate some bearings in some units. When the device got hot this caused the lube to be too thin and the mechanics would slide more freely than originally designed causing oscillation. When the lube cooled it got too thick and the operation was sluggish.
Solution: replace the PID loop parameters with two sets of parameters and look at oscillation to determine which set to use.
I did the same thing on a project back in the 90's. In my case, the problem occurred during startup, turning on a daughter card with plenty of decoupling caps. Inrush to charge the caps dropped supply voltage enough to trigger the power monitor chip. That reset the system, which proceeded to turn on the daughter card, ... lather, rinse, repeat.
I didn't exactly PWM, but pretty close - a slightly different kind of duty cycle modulation with the same net effect.
Nice example of how a seemingly innocuous change can suddenly turn into a butt-biting alligator snapper. Good solution with software PWM. Someone (other than management) should have received a bonus for creative thinking.
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