Infineon XDPL8218, Руководство по конструкции

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Design Guide 26 of 48 V 1.0
2018-06-06
XDPL8218 design guide
For high power factor flyback converter with constant voltage output
Regulated mode parameters
14 Regulated mode parameters
In regulated mode, XDPL8218 supports multi-mode operation consisting of QRM1, Discontinuous Conduction
Mode (DCM) without valley switching, and ABM. The mode of operation and switching parameters are selected
mainly based on the digitally filtered FB voltage V
FB,filtered
mapping. When the regulated mode is entered after
the start-up phase, the filtered FB voltage maximum limit V
FB,filtered,max
ramp is applied initially on the voltage
mapping, to prevent excessive output rise overshoot.
14.1 Digital notch filter
In QRM1 and DCM, a digital notch filter with quality factor of N
quality
is applied, to suppress the double line
frequency component in V
FB,filtered
, in order to achieve high power quality. To allow time for the notch filter
convergence, the notch filter output is only taken as V
FB,filtered
for output regulation after every HV pin line
synchronization has been established for a time-out, which is based on the n
notch,blank
parameter. A digital low
pass filter is used for noise filtering whenever the digital notch filter output has not been taken as V
FB,filtered
. The
recommended N
quality
and n
notch,blank
parameter configuration from Table 5 is selected in this design example.
In ABM, line synchronization and notch filter are disabled for power saving, so a digital low pass filter is applied.
Table 5 Notch filter parameter configuration
Parameter name Recommended value Unit
N
quality
1.6 –
n
notchblank
2 Number of AC input half sine wave period
14.2 On-time limit and switching frequency limit (QRM1/DCM)
The maximum on-time variable t
on,max
(V
in
) is dependent on the estimated input voltage V
in
, as shown in Figure
17 . When V
in
is V
in,low
, the maximum on-time is based on the t
on,max,at,V,in,low
parameter. When V
in
is above V
in,low
, the
maximum on-time is reduced, to compensate for the increasing input voltage influence on the FB gain. When
V
in
is below V
in,low
, the maximum on-time foldback can be configured based on the P
foldback,gain
parameter, for
power limitation during brown-out.
V
in,low
V
inUV
V
inOV
t
on,max,at,V,in,low
t
on,min
t
on,max
(V
in
)
t
on,min,V,out,sense
(V
in
)
P
foldback,gain
=0
0
P
foldback,gain
=1
P
foldback,gain
>1
t
on,min
(V
in
)
Note:
If V
in
≤ V
in,low
, t
on,max
(V
in
) = t
on,max,at,V,in,low
· [1 - P
foldback,gain
· (V
in,low
- V
in
) / V
in,low
]
t
on,min,V,out,sense
(V
in
) = t
demag,min
· (N
p
/ N
s
) · (V
outOV
/ V
in,peak
)
`
If V
in
≥ V
in,low
, t
on,max
(V
in
) = t
on,max,at,V,in,low
· (V
in,low
/ V
in
)
V
in
Figure 17 QRM1 and DCM on-time limits