Introduction to Digital Power Conversion
XMC4000/1000 Family
Modulation
Application Guide 58 V1.0, 2015-01
6.2.3 Discontinuous to Continuous Current Recovery by Timer-Load
If the inductor current reaches 0 (i.e. if the stored magnetic energy in the inductor is entirely
consumed by the load, before the successive PWM starts loading it again), then the switch mode has
entered Discontinuous Conduction Mode (DCM), where the steady state duty-cycle-to-output I
OUT
is
not due.
Discontinuous to Continuous Recovery by Critical Current Mode (CRM) Detection
DCM can be avoided by adding an overall control of the MOSFET on-time, on a Zero Crossing
Detection (ZCD).
Such events will frontload the PWM on-time start and shorten the PWM cycle period, increasing the
duty-cycle intermediately, ahead of the software reaction.
Figure 43 Average Current Control – Discontinuous Current Avoidance
Frontload of PWM cycle by the Timer-Load Input Function on External Event Control
The external event controlled timer input function, called Timer-Load, is suitable for frontload
operations (performing a kind of phase-shift: The on-time front edge is moved to the event time point).
The PWM frontload is executed by hardware: Timer-Load with the compare register CR1 value, on a
ZCD.
The CR1 value defines the Duty-Cycle and the CR2 =
1
/
2
CR1 value defines the ACC sampling points.
The continuous current is recovered by the next PWM cycle with the ‘Next CR1/-CR2’ setup.
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