ML4865 Datasheet, PDF (9/10 Pages) Fairchild Semiconductor – High Voltage High Current Boost Regulator

DESIGN EXAMPLE
In order to design a boost converter using the ML4865,
it is necessary to define the values of a few parameters.
For this example, assume the following design
parameters:
V_IN = 4.75 to 5.25V
V_OUT = 12V
I_OUT(MAX) = 150mA
Shutdown required
First, it must be determined whether the ML4865 is
capable of delivering the output current without an
external Schottky rectifier. This is done using Equation 1:
21 6 7 ^I_OUT(MAX)
@
V_IN
V_OUT
™
0.05 ™ V_IN + 0.4 ™ 0.65
20 5 7 ^I_OUT(MAX)
@
5.25
12
™
0.05 ™ 5.25 + 0.4 ™ 0.65 = 188mA
Next, select an inductor. As previously mentioned, the
recommended inductance is 22µH. Make sure that the
peak current rating of the inductor is at least 1.5A, and
that the DC resistance of the inductor is in the range of
110 to 220mW. A Sumida CD75-220 meets these
requirements.
Finally, the value of the output capacitor is determined
using Equation 2:
C_OUT
=
10 ™ L
V_OUT
=
10
™ 22mH
12V
=
18.3mF
The closest standard value would be a 22µF capacitor
with an ESR rating of 200mW. An AVX
TPSD226M025R0200 would be a good choice.
As mentioned previously, the use of an input supply
bypass capacitor is highly recommended. Since the
output capacitance meets the minimum input
capacitance recommended it can also be used for the
input.
ML4865
9