MAX16841ASA+T Maxim Integrated Products, MAX16841ASA+T Datasheet - Page 12

• Manufacturer Part Number: MAX16841ASA+T
• Description: LED Drivers Wide Input Offline LED Driver with Dim
• Manufacturer: Maxim Integrated Products

Choose the transformer’s magnetizing inductance (Lm)
in such a way so that the transformer operates in DCM
above 120V AC input. DCM operation at higher voltages
reduces switching losses in the Q4 MOSFET. Use the fol-
lowing equation to calculate Lm:
where D is the switching duty cycle at 170V DC and f
is the switching frequency.
In DCM conditions, the peak current in Lm can be
calculated with the help of the following equation:
where V
The switching converter small-signal transfer function
contains a pole at origin and a zero. The zero location
is inversely related to inductor current and inductance
value. The minimum frequency of the zero location is:
Design the loop compensation in such a way so that the
loop crossover is near f
zero formed by R17 and C4 at f
INmax
Controller IC for Dimmable Offline LED Lamps
is the maximum peak input voltage.
f
C4
Zmin
I
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P
R17
Lm
=
=
2
I
=
IN
=
Nonisolated Buck (R17, C3, C4)
2 I
=
× π ×
2
I
Feedback Compensation
×
Zmin
=
I
IN
170V D
G
× π × ×
Lmax
Lm f
IN
P
m
×
340V
IN
f
V
Zmin
f
×
. Place the compensation
×
×
SW
5
LED
L I
× π
×
V
Loop Compensation for
×
V
Zmin
SW
INmax
P P
R20
×
−
×
Lmax
2
2
R17
/5. R20 is given by:
SW
where G
amplifier and V
Place the compensation pole formed by R17 and
C3 at 5 x f
The switching converter small-signal transfer function is
identical to the buck transfer function. The zero location
is inversely related to primary-magnetizing inductance
and its current. The minimum frequency of the zero
location is:
Design the loop compensation in such a way so that the
loop crossover is near f
zero formed by R17 and C4 at f
where Lm is the magnetizing inductance of the flyback
transformer, G
error amplifier, and V
Place the compensation pole formed by R17 and
C3 at 5 x f
=
m
Zmin
Zmin
is the transconductance of the internal error
f
Zmin
m
:
:
P-P
C3
C3
C4
is the transconductance of the internal
R17
=
=
is 2.4V.
=
2
2
2
P-P
× π × ×
2
× π × ×
× π ×
=
for Flyback Driver (R17, C3, C4)
× π ×
I
is 2.4V.
Lmmax
Zmin
G
V
5 f
5 f
Lm I
m
LED
f
Zmin
. Place the compensation
×
1
5
1
×
Zmin
Zmin
V
Zmin
MAX16841
×
Lmax
P P
R20
−
×
Loop Compensation
×
×
R17
/5. R20 is given by:
R17
R17
×
N
N
P
S