MP1410
2A Step Down
DC to DC Converter
MPS
Functional Description
The MP1410 is a current-mode step-down
switch-mode regulator.
It regulates input
voltages from 4.75V to 15V down to an output
voltage as low as 1.22V, and is able to supply
up to 2A of load current. The MP1410 uses
current-mode control to regulate the output
voltage. The output voltage is measured at FB
through a resistive voltage divider and
amplified through the internal error amplifier.
The output current of the transconductance
error amplifier is presented at COMP where a
network compensates the regulation control
system. The voltage at COMP is compared to
the switch current measured internally to
control the output voltage.
The converter uses an internal n-channel
MOSFET switch to step down the input voltage
to the regulated output voltage. Since the
MOSFET requires a gate voltage greater than
the input voltage, a boost capacitor connected
between SW and BS drives the gate. The
capacitor is internally charged while the switch
is off. An internal 10Ω switch from SW to GND
is used to insure that SW is pulled to GND
when the switch is off to fully charge the BS
capacitor.
Inductor
The inductor is required to supply constant
current to the output load while being driven by
the switched input voltage. A larger value
inductor results in less ripple current that in
turn results in lower output ripple voltage.
However, the larger value inductor has a larger
physical size, higher series resistance, and/or
lower saturation current. Choose an inductor
that does not saturate under the worst-case
load conditions. A good rule for determining
the inductance is to allow the peak-to-peak
ripple current in the inductor to be
approximately 30% of the maximum load
current.
Also, make sure that the peak
inductor current (the load current plus half the
peak-to-peak inductor ripple current) is below
the 2.4A minimum current limit. The
inductance value can be calculated by the
equation:
L = (V
OUT
) * (V
IN
-V
OUT
) / V
IN
* f *
∆I
Where V
OUT
is the output voltage, V
IN
is the
input voltage, f is the switching frequency, and
∆I
is the peak-to-peak inductor ripple current.
Table 2 lists a number of suitable inductors
from various manufacturers.
Table 2: Inductor Selection Guide
Core
Type
Core
Material
Package
Dimensions (mm)
W
L
H
7.0
7.3
5.5
5.5
6.7
10.1
5.0
7.6
10.0
9.7
9.4
9.4
7.8
8.0
5.7
5.7
6.7
10.0
5.0
7.6
10.0
11.5
13.0
13.0
5.5
5.2
5.5
5.5
3.0
3.0
3.0
5.1
4.3
4.0
3.0
5.1
Application Information
The output voltage is set using a resistive
voltage divider from the output voltage to FB
(see Figure 3). The voltage divider divides the
output voltage down by the ratio:
V
FB
= V
OUT
* R3 / (R2 + R3)
Vendor/Model
Sumida
CR25
CDH74
CDRH5D28
CDRH5D28
CDRH6D28
CDRH104R
Toko
D53LC Type A
D75C
D104C
D10FL
Coilcraft
DO3308
DO3316
Thus the output voltage is:
V
OUT
= 1.222 * (R2 + R3) / R3
Open
Open
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Open
Open
Open
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
R3 can be as high as 100KΩ, but a typical
value is 10KΩ.
Using that value, R2 is
determined by:
R2 ~= 8.18 * (V
OUT
– 1.222) (KΩ)
For example, for a 3.3V output voltage, R3 is
10KΩ, and R2 is 17KΩ.
MP1410 Rev 1.6_ 07/25/03
4
MPS [ MONOLITHIC POWER SYSTEMS ]
