Infineon XDPL8218, Design Manual

Page: 12 / 48

Design Guide 12 of 48 V 1.0
2018-06-06
XDPL8218 design guide
For high power factor flyback converter with constant voltage output
MOSFET maximum current cycle-by-cycle limit and start-up phase design
𝑽
𝑶𝑪𝑷𝟏,𝒂𝒕,𝑽,𝒊𝒏,𝒍𝒐𝒘
= 𝟎. 𝟓𝟐 𝑽
V
OCP1,at,V,in,high
parameter defines the value of V
OCP1
(V
in
) variable when the estimated input voltage V
in
is the same
as or higher than the highest operational input voltage parameter V
in,high
. To better limit the maximum output
power transfer to the LEDs under the fault condition mentioned above, V
OCP1,at,V,in,high
should be configured less
than V
OCP1,at,V,in,low
.
V
in,high
and V
OCP1,at,V,in,high
parameters can be defined and calculated as:
𝑉
𝑖𝑛,ℎ𝑖𝑔ℎ
= 𝑏 ∙ 𝑉
𝐴𝐶,𝑚𝑎𝑥
(17)
Where b is the ratio recommended to be between 1.05 and 1.10.
Taking b = 1.07,
𝑉
𝑖𝑛,ℎ𝑖𝑔ℎ
= 1.07 ∙ 305
𝑽
𝒊𝒏,𝒉𝒊𝒈𝒉
= 𝟑𝟐𝟔 𝑽
𝒓𝒎𝒔
𝑉
𝑂𝐶𝑃1,𝑎𝑡,𝑉,𝑖𝑛,ℎ𝑖𝑔ℎ
= 𝑐 ∙ 𝑅
𝐶𝑆
∙ 𝐿
𝑝
∙ 𝐼
𝑝𝑟𝑖(𝑝𝑘),𝑚𝑎𝑥
2
∙ 𝑓
𝑠𝑤,𝑚𝑖𝑛,𝑎𝑡,𝑃,𝑜𝑢𝑡,𝑓𝑢𝑙𝑙
∙ [
1
𝑉
𝑖𝑛,ℎ𝑖𝑔ℎ (𝑝𝑘)
+
1
𝑁 ∙ (𝑉
𝑜𝑢𝑡,𝑠𝑒𝑡𝑝𝑜𝑖𝑛𝑡
+ 𝑉
𝑑
)
]
(18)
Where V
in,high(pk)
is √2 times of V
in,high
and c is the ratio recommended to be between 1.05 and 1.15.
Taking c = 1.12,
𝑉
𝑂𝐶𝑃1,𝑎𝑡,𝑉,𝑖𝑛,ℎ𝑖𝑔ℎ
= 1.12 ∙ 0.2 ∙ 544 ∙ 10
−6
∙ 2.606
2
∙ 52 ∙ 10
3
∙ [
1
√2 ∙ 326
+
1
3.2 ∙ (54 + 0.7)
]
𝑽
𝑶𝑪𝑷𝟏,𝒂𝒕,𝑽,𝒊𝒏,𝒉𝒊𝒈𝒉
= 𝟎. 𝟑𝟒 𝑽
Note: V
OCP1,at,V,in,high
parameter minimum configurable value is fixed as 0.34 V. If the calculation result of
equation (18) is below 0.34 V, parameter setting of V
OCP1,at,Vin,high
= 0.34 V should be selected.
V
start,OCP1
0
2 t
SS
time
Soft start phase
(based on n
ss
= 3 configuration as example)
Output
charging
phase
Pre-Startup Check
(e.g. input voltage,
IC temperature)
t
SS
t
out,charge
V
out,start
Startup phase
3 t
SS
V
OCP1
(V
in
)
Start of regulation according to
feedback voltage mapping
V
out
CS pin voltage level 1 for MOSFET
max current cycle by cycle limit
Voltage
(0.5ms typ.) (1.0ms typ.) (1.5ms typ.)
V
OCP1,init
Startup with 1
st
soft start step
Regulated Mode
V
outUV,start
t
start,max
Figure 8 Pre-start-up check, start-up phase and regulated mode
Pre-start-up check ensures the estimated input voltage V
in
and IC junction temperature T
j
are within the
configured protection limits before start-up, as shown in Figure 8 . The parameter configurations of the input
voltage levels and maximum T
j
for start-up are covered in Section 11 and Section 15.3 respectively.