Design Guide
30 of 48
V 1.0
2018-06-06
XDPL8218 design guide
For high power factor flyback converter with constant voltage output
Other protection-related parameters
15
Other protection-related parameters
15.1
V
CC
OVP
The V
CC
Over Voltage Protection (OVP) reaction is configurable to latch-mode or auto-restart, based on the
Reaction
VCC,OVP
parameter, while the V
CC
OVP level is configurable based on the V
VCC,max
parameter.
Reaction
VCC,OVP
= Latch-Mode and V
VCC,max
= 23 V are recommended and selected in this design example. Based
on V
VCC,max
= 23 V, V
CC
capacitor voltage rating of 25 V is selected.
15.2
Regulated mode V
CC
UVP
EN
VCC,UVP
parameter refers to the enable switch for the regulated mode V
CC
Under Voltage Protection (UVP). The
protection reaction is fixed as auto-restart and it is triggered when V
CC
voltage is the same as or lower than
regulated mode V
CC
UVP V
VCC,min
, for longer than a blanking period based on t
VCCUV,blank
.
EN
VCC,UVP
= Enabled, V
VCC,min
= 7.5 V and t
VCCUV,blank
= 1.5 ms parameter settings are recommended and selected in
this design example.
15.3
IC over-temperature protection
The IC over-temperature protection level is based on the T
critical
parameter. If T
critical
is configured above 119°C,
the maximum switching frequency parameter f
sw,max
cannot be configured above 136.4 kHz. The protection
reaction is fixed as auto-restart, while the maximum junction temperature for start-up/restart is fixed as 4°C
below T
critical
.
T
critical
= 119°C is recommended and selected in this design example.
Note:
XDPL8218’s lifetime is not guaranteed when operating junction temperature is above 125°C, which
is possible if T
critical
is configured above 119°C, with temperature sensing tolerance of ± 6°C.
15.4
Primary MOSFET over-current protection
V
OCP2
denotes the CS pin voltage level 2 for primary MOSFET over-current protection. Under the single-fault
condition of shorted primary main winding, the primary MOSFET over-current protection is triggered when the
CS pin voltage exceeds V
OCP2
for longer than a blanking time based on the t
CSOCP2
parameter.
t
CSOCP2
= 240 ns is recommended and selected in this design example.
V
OCP2
level is automatically selected based on the V
OCP1,at,V,in,low
. In this design
example, V
OCP1,at,V,in,low
= 0.52 V is selected, so V
OCP2
= 0.8 V is applied. The protection reaction is fixed as auto-
restart.
Table 9
Automatic V
OCP2
level selection based on V
OCP1,at,V,in,low
parameter configuration
V
OCP1,at,V,in,low
configuration (V)
V
OCP2
(V)
0.34 ~ 0.36
0.6
0.37 ~ 0.54
0.8
0.55 ~ 0.72
1.2
0.73 ~ 1.08
1.6
