2
Equations to set the parameters
2.1
PFC
2.1.1
PFC power calculation
The device uses an internal numerical representation of the power delivered. The relationship between the
internal value and the true power is as follows:
Equation 1
pinn = P
L
128 ∙ LSBVin2 ∙ Tck
(1)
Where:
•
pinn
is the internal numerical power estimation
•
P
is the real power level
•
L
is the PFC choke inductance value
•
LSBVin
= 1.89 V
•
Tck
= 16.66 ns
Note that this relation is a loose approximation due to the PFC parasitics, which offset the true power level.
2.1.2
PFC compensation parameters
The PFC compensation is calculated at each line valley (i.e. input mains zero crossing). The device uses the
following formula to calculate the power
Equation 2
pinn = 2 ∙ Kp + Ki
1
1 − z−1
err
(2)
where
err
is equal to the voltage error (target output voltage - real output voltage) divided by Verr
LSB
= 0.473 V.
2.2
LLC
The LLC compensation is based on an analog circuitry at the secondary side.
The time shift value applied by the controller is calculated using the sampled value on the LLC_FB pin.
Equation 3
TS = 0.5 ∙
VFB
LSBVFB − FBOS
(3)
where:
•
TS = time shift value applied to LLC SMEDs (in 60 MHz clock ticks)
•
V
FB
= Voltage on the LLC_FB pin
•
LSB
VFB
= 2.44 mV (used to convert the LLC_FB voltage value in the internal numerical format)
•
FBos = fixed offset (68)
UM3002
Equations to set the parameters
UM3002
-
Rev 1
page 3/42