Introduction to Digital Power Conversion
XMC4000/1000 Family
Modulation
Application Guide
72
V1.0, 2015-01
6.6
CCM, CRM (CrCM) and DCM
In a switch mode DC/DC converter, there are two DC voltages with different polarities toggling across
the inductor. Depending on polarity, the current will rise or fall linearly, due to the self-inductance. The
inductor energy will grow during one voltage polarity and be consumed by the load during the other.
The unloading current of inductor energy cannot last longer than reaching 0, due to rectification; i.e. if
the magnetic energy reaches zero, there will be no current until the loading phase appears again.
This phenomenon defines three different current modulation state modes:
Continuous-Conduction-Mode (CCM)
−
The current is always on, and slope may change direction
CrCM, Critical-Conduction-Mode (CRM)
−
The current hits zero and is just about to change direction
Note:
CRM, CrCM, Critical-Conduction-Mode is today often also referred to as Boundary Mode (BRM).
Discontinuous Conduction Mode (DCM)
−
The current hits zero and is cut-off until it change direction
Figure 57
Modulation Mode
– CCM – CRM (CrCM, BRM) – DCM – (Reference: Buck Converter)
The magnetic load/unload balancing criteria is illustrated by the Voltage Time Areas: A
+
=A.
The theoretical explanation behind this criteria is described in the next section.
