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User Manual
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V 1.0
2021-08-25
XDPP1100 technical reference manual
Digital power controller
Flux balance (FBAL)
Figure 94
Example PI magnitude plot for kp_fbal = 48, ki_fbal = 32, F
switch
= 250 kHz
12.3
Flux balance FW override
The flux balance output, fbal_duty_adj, may be overridden through the following registers (where X = 1, 2):
•
fbalX_fw_en
•
fbalX_fw_adj
These overrides could be used as part of a user-written FW patch to implement a different current balance
scheme.
12.4
Flux balance DCM operation
At light current load, the output inductor current flows in a negative direction if FETs are employed as the
secondary rectifier (SR) devices. If the SR FETs are disabled or diodes are used in their place, the inductor
current is discontinuous. In this discontinuous conduction mode (DCM), the V
RECT
rising edge can occur prior to
the primary PWM rising edge due to the negative inductor current driving V
RECT
high. This means the V
RECT
pulse
width is no longer a good indication of the primary-side PWM pulse width mismatch between the half-cycles.
Therefore, due to the inability to accurately measure the primary-side pulse width in DCM operation it is
recommended to disable flux balance in this mode.
The XDPP1100 provides several registers to control the flux balance behavior in and around DCM operation.
These registers are:
-60
-50
-40
-30
-20
-10
0
10
100
1000
10000
100000
|H
p
i|
(d
B
)
Frequency (Hz)
Flux balance PI filter
(F
switch
=250 kHz, kp_fbal=48, ki_fbal=32)