MP3209 MPS, MP3209 Datasheet - Page 7

• Manufacturer Part Number: MP3209
• Description: 1.4mhz, 350ma Boost Converter
• Manufacturer: MPS

APPLICATIONS INFORMATION
COMPONENT SELECTION
Setting the Output Voltage
Set the output voltage by selecting the resistive
voltage divider ratio. Use 510kΩ for the high-
side resistor R1 of the voltage divider.
Determine the low-side resistor R2 by the
equation:
where V
resistor R3 and C3 to improve the transient
performance.) (Figure 2)
Selecting the Input Capacitor
An input capacitor is required to supply the AC
ripple current to the inductor, while limiting noise
at the input source. This capacitor must have low
ESR, so ceramic is the best choice.
Use an input capacitor value of 4.7μF or greater.
This capacitor must be placed physically close
to the IN pin. Since it reduces the voltage ripple
seen at IN, it also reduces the amount of EMI
passed back along that line to the other circuitry.
Selecting the Output Capacitor
A single 4.7μF to 10μF ceramic capacitor
usually provides sufficient output capacitance
for most applications. If larger amount of
capacitance is desired for improved line support
and transient response, tantalum capacitors
can be used in parallel with the ceramic. The
impedance of the ceramic capacitor at the
switching frequency is
capacitance, and so the output voltage ripple is
mostly independent of the ESR. The output
voltage ripple V
Where V
current, C2 is the capacitance of the output
capacitor, and f
frequency.
MP3209 Rev.0.93
9/21/2007
(It is recommended to add feed-forward
OUT
IN
is the input voltage, I
V
is the output voltage.
RIPPLE
R2
RIPPLE
MPS CONFIDENTIAL AND PROPRIETARY INFORMATION – INTERNAL USE ONLY
SW
=
=
I
LOAD
V
is calculated as:
V
is the 1.4MHz switching
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
R1
O
OUT
UT
(
×
V
×
−
V
dominated
O
C
V
UT
FB
2
FB
×
−
f
LOAD
V
SW
IN
)
is the load
© 2007 MPS. All Rights Reserved.
by
www.MonolithicPower.com
the
MP3209 – 1.4MHZ, 350mA BOOST CONVERTER
Selecting the Inductor
The inductor is required to force the output
voltage higher while being driven by the lower
input voltage. Choose an inductor that does not
saturate at the SW current limit. A good rule for
determining the inductance is to allow the peak-
to-peak ripple current to be approximately 30%-
50% of the maximum input current. Make sure
that the peak inductor current is below 75% of
the typical current limit at the duty cycle used to
prevent loss of regulation due to the current
limit variation.
Calculate the required inductance value L using
the equations:
Where I
is the peak-to-peak inductor ripple current, and η
is
recommended for input voltages less than 3.3V
and 22µH for inputs greater than 3.3V.
Selecting the Diode
The output rectifier diode supplies current to the
inductor when the internal MOSFET is off. To
reduce losses due to diode forward voltage and
reverse recovery, use a Schottky diode. Choose a
diode whose maximum reverse voltage rating is
greater than the maximum output voltage. For
output voltage less than 20V, it is recommended
to choose the CMH5H-3 for most applications.
This diode is used for load currents less than
300mA. For ultra-low-profile applications, choose
BAT54-02 Schottky diode. Use two BAT54-02 in
parallel for high load current.
efficiency.
LOAD(MAX)
I
IN
Δ
(
MAX
I
L
=
For
is the maximum load current, ΔI
=
(
)
30
=
V
V
%
IN
OUT
V
OUT
(V
the
−
50
OUT
×
V
×
f
SW
%
IN
I
LOAD
MP3209,
-
)
×
I
V
IN
×
η
IN
(
Δ
MAX
(
)
MAX
I
)
)
10µH
is
7