An368 – Cirrus Logic AN368 User Manual
Page 55
AN368
AN368REV2
55
Calculate the MOSFET ‘ON’ time T1
CH1
in Mode 1 using Equation 20:
Calculate the MOSFET ‘ON’ time T1
CH2
in Mode 2 using Equation 21:
Calculate the MOSFET ‘OFF’ time T2
CH1
in Mode 1 using Equation 22:
Calculate the MOSFET ‘OFF’ time T2
CH2
in Mode 2 using Equation 23:
f. Calculate the Flyback Primary-side Inductance
Calculate the flyback transformer primary-side inductance, L
P
, using Equation 24:
g. Calculate Peak Current on the Flyback Primary-side
Calculate peak current I
PK1(FB)
during Mode 1 using Equation 25:
Calculate peak current I
PK2(FB)
during Mode 2 using Equation 26:
Calculate the average current I
MODE1(avg)
during Mode 1 using Equation 27:
Calculate the average current I
MODE2(avg)
during Mode 2 using Equation 28:
T1
CH1
TT
CH1
T3
CH1
–
D
MODE1
14.29
s 0.37
5.3
s
=
=
=
[Eq. 99]
T1
CH2
TT
CH2
T3
CH2
–
D
MODE2
18.76
s 0.22
4.2
s
=
=
=
[Eq. 100]
T2
CH1
TT
CH1
T1
CH1
–
T3
CH1
–
15.29
s 5.3s
–
1
s
–
9.0
s
=
=
=
[Eq. 101]
T2
CH2
TT
CH2
T1
CH2
–
T3
CH2
–
19.76
s 4.2s
–
1
s
–
14.6
s
=
=
=
[Eq. 102]
L
P
N
2
V
BST
2
V
MODE1
2
V
BST
N V
MODE1
+
2
I
MODE1
TT F
sw1
2
-----------------------------------------------------------------------------------------------------------------------
=
[Eq. 103]
5.57
2
=
200V
2
20.95V
2
200V
5.57 20.95V
+
2
213mA 35.05
s 70kHz
2
-------------------------------------------------------------------------------------------------------------------------------------------------------------
3543
H
=
I
PK1 FB
V
BST
T1
CH1
L
P
----------------
200V
5.3
s
3543
H
---------------------
299mA
=
=
=
[Eq. 104]
I
PK2 FB
V
BST
T1
CH2
L
P
----------------
200V
4.2
s
3543
H
---------------------
237mA
=
=
=
[Eq. 105]
I
MODE1 avg
I
PK1 FB
N
T2
CH1
2 TT
----------------
299mA 5.57
9.0
s
2 35.05
s
------------------------------
214mA
=
=
=
[Eq. 106]
I
MODE2 avg
I
PK2 FB
N
T2
CH2
2 TT
----------------
237mA 5.57
14.7
s
2 35.05
s
------------------------------
277mA
=
=
=
[Eq. 107]