MAX15005 Maxim Integrated Products, MAX15005 Datasheet - Page 16

• Manufacturer Part Number: MAX15005
• Description: (MAX15004 / MAX15005) 4.5V to 40V Input Automotive Flyback/Boost/SEPIC Power-Supply Controllers
• Manufacturer: Maxim Integrated Products

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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
FET plus the voltage drop across the inductor ESR. ΔI
is peak-to-peak inductor ripple current as calculated
above. ΔV
4.5V to 40V Input Automotive
Flyback/Boost/SEPIC Power-Supply Controllers
Figure 5. Application Schematic
16
DS
Input Capacitor Selection in Boost Configuration
is the total voltage drop across the external MOS-
______________________________________________________________________________________
Q
V
IN
is the portion of input ripple due to the
C
IN
ESR
C
Δ
C
IN
I
FF
L
RF
=
=
=
CT
RT
4 f
(V
Δ
V
×
Δ
IN
CF
ESR
L f
I
L
Δ
OUT
−
×
C
0.1μF
I
REG5
V
L
OUT
DS
×
11
10
×
6
D
) ) D
Δ
×
RTCT
COMP
FB
V
13
SLOPE
Q
REG5
4
C
MAX15004A/B
MAX15005A/B
SLOPE
D
VIN
1
9
SS
IN
C
OUT
L
V
SS
CS
CC
16
15
12
C
1μF
VIN
capacitor discharge and ΔV
to ESR of the capacitor. Assume the input capacitor rip-
ple contribution due to ESR (ΔV
charge (ΔV
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.
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.
Output Capacitor Selection in Boost Configuration
C
CS
R
D
C
4.7μF
VCC
VCC
VCC
R
CS
Q
) is equal when using a combination of
PGND
Q
L
RS
D3
ESR
ESR
is the contribution due
C
OUT
) and capacitor dis-
V
RA
RB
OUT
18V
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