MC44608
EQUATION 1
Start–up Phase Duration:
C
(V
UVLO2)
stup
Vcc
t
start–up
I
stup
where: I
is the start–up current flowing through V
pin
CC
stup
C
is the V capacitor value
Vcc
CC
EQUATION 2
Switching Phase Duration:
C
(V
stup
UVLO1)
Vcc
t
switch
I
I
ccS
G
where: I
is the no load circuit consumption in switching phase
ccS
I
G
is the current consumed by the Power Switch
EQUATION 3
Latched–off Phase Duration:
C
(UVLO1 UVLO2)
I
Vcc
t
latched off
I
ccL
pin3
where: I
is the latched off phase consumption
is the current drawn from pin3 adding a resistor
ccL
I
pin3
EQUATION 4
Burst Mode Duty Cycle:
t
switch
d
BM
t
t
t
start up
switch
latched off
EQUATION 5
C
(V
stup
UVLO1)
Vcc
I
I
ccS
(V
G
d
BM
C
(V
UVLO2)
C
UVLO1)
C
(UVLO1 UVLO2)
stup
I
stup
Vcc
Vcc
Vcc
I
I
I
I
stup
ccS
G
ccL pin3
EQUATION 6
1
d
BM
I
I
I
I
ccS
I
G
ccS
G
1
k
k
S Stup
S L
I
I
stup
ccL pin3
where: k
S/Stup
S/L
= (V
– UVLO2)/(V
– UVLO1)
– UVLO1)
stup
stup
k
= (UVLO1 – UVLO2)/(V
stup
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