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All figures used in the slides are from National Semiconductor Analog University
http://webench.national.com/en/power/analogu.html
In a real converter, when the load current steps down, the excessive energy of an output inductor has to be
delivered to the output capacitor, causing the output voltage spikes. When the load current steps up, the
inductor restores its energy while the output capacitor supplies the load, causing the output voltage sags.
fc = 27 kHz
m= 8 deg.
100mv/Div
400mA
200mA
Transient response A is slower than B because its crossover frequency is lower than B's.
Transient response C and D have rings because of the small phase margin.
The hysteretic regulator does not have compensation circuitry that requires an accurate design in the
whole input-voltage, output-voltage, temperature, and load-current range. This compensation can be
further complicated if additional capacitors are added to the output of the voltage regulator around the
microprocessor package.
The main problem associated with the hysteretic type regulator relates to the ability to predict its
switching frequency due to the dependence of this parameter on the output filter characteristics and
circuit operation.
Hysteretic controllers have excellent load current transient-response characteristics compared to the
other types of controllers (such as PWM voltage and current mode) with slow feedback loops. The
controllers react to transients within the same cycle in which the transient occurs and keep the
corresponding FET in an on-state until the output voltage returns to the required dc level. Thus a
minimum number of bulk output capacitors are required, saving total system cost.