Staying In The Window
In addition to budgeting the error sources to meet their own priorities, savvy designers will read between the lines of the spec, and violate it selectively where and when it makes sense to do so (at this moment the author offers up a prayer to the great CPU god that he will not strike the author down for his insolence). For example, it's usually not necessary to maintain ±2% dc accuracy when the load is less than one-quarter of the full load. Instead, it's allowable (and actually desirable for better transient response) to let the output float, perhaps 1% high, when in light-load, pulse-skipping mode.
The upper limit of the voltage window is determined by the thermal limitations of the CPU. The CPU manufacturers will also say that you shouldn't exceed this value because that's the point where the CPU is tested. Realistically, however, allowing the voltage to float 1% high under light loads isn't going to hurt anything. Similarly, a momentary 1% overshoot when going from heavy to light load isn't going to be a problem. The upper limit of the voltage window is really determined by thermal issues, not transients.
In contrast, the lower limit to the voltage window is a much more sacred barrier. If the voltage ever dips below the magic line, even for a microsecond, data may be corrupted, and the computer may lock up. So, don't push your luck on the lower limit. Improve the transient response of your converter by reducing the inductor value until all the bad effects of high inductor ripple become a headache, back off a little, then pile on the local bypass capacitors to finish the job of staying within the window.
Staying In The Window
In addition to budgeting the error sources to meet their own priorities, savvy designers will read between the lines of the spec, and violate it selectively where and when it makes sense to do so (at this moment the author offers up a prayer to the great CPU god that he will not strike the author down for his insolence). For example, it's usually not necessary to maintain ±2% dc accuracy when the load is less than one-quarter of the full load. Instead, it's allowable (and actually desirable for better transient response) to let the output float, perhaps 1% high, when in light-load, pulse-skipping mode.
The upper limit of the voltage window is determined by the thermal limitations of the CPU. The CPU manufacturers will also say that you shouldn't exceed this value because that's the point where the CPU is tested. Realistically, however, allowing the voltage to float 1% high under light loads isn't going to hurt anything. Similarly, a momentary 1% overshoot when going from heavy to light load isn't going to be a problem. The upper limit of the voltage window is really determined by thermal issues, not transients.
In contrast, the lower limit to the voltage window is a much more sacred barrier. If the voltage ever dips below the magic line, even for a microsecond, data may be corrupted, and the computer may lock up. So, don't push your luck on the lower limit. Improve the transient response of your converter by reducing the inductor value until all the bad effects of high inductor ripple become a headache, back off a little, then pile on the local bypass capacitors to finish the job of staying within the window.