Introduction to Digital Power Conversion
XMC4000/1000 Family
Modulation
Application Guide
66
V1.0, 2015-01
6.5.3
V
IN
independent Average Current mode
The PCC average current can be maintained in a fast inherent loop, created by a Slope
Compensation of the Peak Current. This loop will react to input voltage variations on a cycle-by-cycle
basis and force the average current towards the target level, before any reaction from the long-term
software control.
The demonstration here shows how an inherent control loop by Peak Current Slope Compensation
will settle the average current back on to the target level again, after some damped oscillations in a
few cycles, even on a very drastic input voltage step from one cycle to another. No SW is involved.
Figure 50
Slope Compensation
– V
IN
independent Average Current Mode Control PCC
Inductor Current and Slope Compensation characteristics for Fixed Average Current PPC
1.
Define the average current level by the end-point of the Peak Current compensation ramp (i.e. at
the cycle period end T)
2.
Set Slope Compensation “-s
C
” = -
½
V
OUT
/
L, (i.e half the falling I
L
slope). This will center the
∆I
L
ripple range on the peak-current end-point level.
Variables used in the V
IN
-Independent Average Current by Slope Compensation exmple
Rising inductor current (I
L
) slope by Input voltage V
IN1
s
A1
= (V
IN1
-V
OUT
)
/
L
Rising inductor current (I
L
) slope by Input voltage V
IN2
s
A2
= (V
IN2
-V
OUT
)
/
L
Falling
inductor
current
(I
L
)
slope
by
output
voltage
V
OUT
-
s
B
=
-
V
OUT
/
L
(
short term constant
)
Peak Current (I
PEAK
) characteristic: Slope Compensation
-
s
C
=
-
½
s
B
=
-
½
V
OUT
/
L
(
condition
)
Time-Out (by timer compare) limits I
L
rising time T-t
OFF
min
T-t
OFF
min
= MOSFET Off-time minimum
