mp6001dn MPS, mp6001dn Datasheet - Page 9

• Manufacturer Part Number: mp6001dn
• Description: Monolithic Flyback/forward Dc-dc Converter
• Manufacturer: MPS

2. Ripple Factor of the Magnetizing Current
The conduction loss in S, D2, the transformer,
the snubber, and in the ESR of the input/output
capacitors will increase as the ripple of the
magnetizing current increases. The ripple factor
(K
ripple current vs. the average current as shown
in Figure 3.
Where I
output current;
The
increase with a high ripple factor, which makes
the filter bigger and more expensive. On the
other hand, it can help to minimize the turn-on
loss of S and reverse-recovery loss due to D2.
With nominal input voltage, K
at 60%~120% for most DC-DC converters.
The primary side (or magnetizing) inductance
can be determined by:
3. Core Selection
Pick a core based on experience or through a
catalog (Refer to http://www.ferroxcube.com).
Select an ER, EQ, PQ, or RM core to minimize
the transformer’s leakage inductance.
4. Winding Selection
MP6001 Rev. 0.91
9/21/2007
I
M
r
Transformer (Reflected to Primary Side)
) is defined as the ratio of the peak-to-peak
Figure 3—Magnetic Current of Flyback
input/output
0
M
can be derived either from input or
TM
I
M
L
F
=
DT
=
I
D
K
IN
S
ripple
V
r
=
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
IN
=
K
N
×
Δ
I
r
I
M
×
M
D
I
×
M
1 (
I
I
I
D2
0
×
M
voltage
−
T
/N
r
D
S
T
)
can be selected
MP6001 – MONOLITHIC FLYBACK/FORWARD DC-DC CONVERTER
S
will
© 2007 MPS. All Rights Reserved.
MP6001_F03
www.MonolithicPower.com
also
Solid wire, Litz wire, PCB winding, Flex PCB
winding or any combination thereof can be used
as
applications, solid wire is the most cost effective
choice. Consider using several wires in parallel
and interleaving the winding structure for better
performance of the transformer.
The number of primary turns can be determined
by:
Where B
density (usually below 300mT) and A
effective area of the core.
The air gap can be estimated by:
5. Right Half Plane Zero
A Flyback converter operating in continuous
mode has a right half plane (RHP) zero. In the
frequency domain, this RHP zero adds not only
a phase lag to the control characteristics but
also increases the gain of the circuit. Typical
rule of thumb states that the highest usable
loop crossover frequency is limited to one third
the value of the RHP zero. The expression for
the location of the RHP zero in a continuous
mode flyback is given by:
Where R
magnetizing inductance on transformer primary
side, and N is the transformer’s turn ratio.
Reducing the primary inductance increases the
RHP zero frequency which results in higher
crossover frequencies.
transformer
f
LOAD
RHPZ
MAX
is the load resistance, L
Gap
=
is the allowed maximum flux
N
R
P
LOAD
winding.
=
=
μ
B
o
×
MAX
L
×
2
F
N
π
L
1 (
×
×
2
F
×
I
−
P
A
×
L
For
D
F
E
A
)
×
2
E
D
×
low
N
2
E
F
current
is the
is the
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