Datasheet
Input Capacitor Selection in Boost Configuration
The input current for the boost converter is continuous
and the RMS ripple current at the input capacitor is low.
Calculate the minimum input capacitor value and maxi-
mum ESR using the following equations:
where:
V
DS
is the total voltage drop across the external MOS-
FET plus the voltage drop across the inductor ESR. ΔI
L
is peak-to-peak inductor ripple current as calculated
above. ΔV
Q
is the portion of input ripple due to the
capacitor discharge and ΔV
ESR
is the contribution due
to ESR of the capacitor. Assume the input capacitor rip-
ple contribution due to ESR (ΔV
ESR
) and capacitor dis-
charge (ΔV
Q
) is equal when using a combination of
ceramic and aluminum capacitors. During the convert-
er turn-on, a large current is drawn from the input
source especially at high output to input differential.
The MAX15004/MAX15005 are provided with a pro-
grammable soft-start, however, a large storage capaci-
tor at the input may be necessary to avoid chattering
due to finite hysteresis.
Output Capacitor Selection in Boost Configuration
For the boost converter, the output capacitor supplies
the load current when the main switch is on. The
required output capacitance is high, especially at higher
duty cycles. Also, the output capacitor ESR needs to be
low enough to minimize the voltage drop due to the ESR
while supporting the load current. Use the following
equations to calculate the output capacitor, for a speci-
fied output ripple. All ripple values are peak-to-peak.
I
(V V
L
IN DS
=
−
Δ
))D
Lf
OUT
×
×
C
ID
4f V
ESR
V
I
IN
L
OUT Q
ESR
L
=
×
××
=
Δ
Δ
Δ
Δ
4.5V to 40V Input Automotive
Flyback/Boost/SEPIC Power-Supply Controllers
Figure 5. Application Schematic
MAX15004A/B
MAX15005A/B
IN
C
VCC
4.7μF
R
VCC
D
VCC
D
VIN
R
CS
D3
PGND
Q
L
RS
C
OUT
RB
RA
C
VIN
1μF
REG5
SS
SLOPE
11
6
13
16
15
12
1
4
9
10
RT
CT
V
CC
OUT
CS
V
OUT
RTCT
COMP
C
REG5
0.1μF
V
IN
18V
C
IN
C
CS
C
SS
C
SLOPE
RF
CF
FB
C
FF
MAX15004A/B/MAX15005A/B
16
Maxim Integrated