MP3212 MPS, MP3212 Datasheet - Page 10

• Manufacturer Part Number: MP3212
• Description: 1.3a, 1mhz Step-up Regulator With Integrated Input Disconnect Switch
• Manufacturer: MPS

APPLICATION INFORMATION
Components referenced below apply to
Typical Application Circuit on page 1.
Setting the Output Voltage
Set the output voltage by selecting the resistive
voltage divider ratio. Use 10kΩ for the low-side
resistor R2 of the voltage divider. Determine the
high-side resistor R1 by the equation:
where V
For R2 = 10kΩ and V
R1 (kΩ) = 8.13 x (V
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. A low ESR capacitor is
required to keep the noise at the IC to a
minimum. Ceramic capacitors are preferred, but
tantalum or low-ESR electrolytic capacitors may
also suffice.
Use an input capacitor value greater than 4.7µF.
The capacitor can be electrolytic, tantalum or
ceramic. However since it absorbs the input
switching current it requires an adequate ripple
current rating. Use a capacitor with RMS current
rating greater than the inductor ripple current
(see Selecting The Inductor to determine the
inductor ripple current).
To ensure stable operation, place the input
capacitor as close to the IC as possible.
Alternately a smaller high quality ceramic 0.1µF
capacitor may be placed closer to the IC with the
larger capacitor placed further away. If using this
technique, the larger capacitor can be a tantalum
or electrolytic type. All ceramic capacitors should
be placed close to the MP3212.
Selecting the Output Capacitor
The output capacitor is required to maintain the
DC output voltage. Low ESR capacitors are
preferred to keep the output voltage ripple to a
minimum. The characteristic of the output
capacitor also affects the stability of the
regulation control system. Ceramic, tantalum, or
low
MP3212 Rev. 0.9
3/21/2008
ESR
OUT
is the output voltage.
R1
MP3212–1.3A, 1MHz, STEP-UP REGULATOR WITH INTEGRATED INPUT DISCONNECT SWITHCH
=
electrolytic
R2 (V
OUT
FB
´
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
– 1.23) kΩ.
= 1.23V, then
V
OUT
FB
-
V )
capacitors
FB
© 2011 MPS. All Rights Reserved.
www.MonolithicPower.com
are
recommended. In the case of ceramic capacitors,
the impedance of the capacitor at the switching
frequency is dominated by the capacitance, and
so the output voltage ripple is mostly independent
of the ESR. The output voltage ripple is
estimated to be:
Where V
V
respectively, I
switching frequency, and C
of the output capacitor.
In the case of tantalum or low-ESR electrolytic
capacitors, the ESR dominates the impedance at
the switching frequency, and so the output ripple
is calculated as:
Where R
the output capacitors.
Choose an output capacitor to satisfy the output
ripple and load transient requirements of the
design. A 3.3µF ceramic capacitor is suitable for
most applications.
Selecting the Inductor
The inductor is required to force the higher output
voltage while being driven by the input voltage. A
larger value inductor results in less ripple current
that results in lower peak inductor current,
reducing stress on the internal N-Channel.switch.
However, the larger value inductor has a larger
physical size, higher series resistance, and/or
lower saturation current.
A 10µH inductor is recommended for most
applications. However, a more exact inductance
value can be calculated. A good rule of thumb 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 current limit at the operating
duty cycle to prevent loss of regulation due to the
OUT
V
RIPPLE
are the DC input and output voltages
RIPPLE
»
ESR
(1
V
is the equivalent series resistance of
-
RIPPLE
LOAD
C
is the output ripple voltage, V
V
OUT
V
OUT
IN
´
»
is the load current, f
) I
´
f
æ
ç
ç
ç
ç è
SW
1 -
LOAD
C
V
OUT
V
OUT
IN
OUT
+
´
I
ö ÷
÷ ´
÷
÷
ø
LOAD
is the capacitance
f
SW
I
LOAD
´
R
V
ESR
IN
SW
´
V
IN
is the
OUT
and
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