MAX15004_11 Datasheet, PDF (16/27 Pages) Maxim Integrated Products – 4.5V to 40V Input Automotive Flyback/Boost/SEPIC Power-Supply Controllers

4.5V to 40V Input Automotive
Flyback/Boost/SEPIC Power-Supply Controllers
VIN
CIN
CREG5
0.1μF
RT
13
REG5
DVIN
CVIN
1μF
1
IN
16
VCC
CT
C_FF
RF
CF
6
RTCT
MAX15004A/B
MAX15005A/B
OUT ¹⁵
11 _COMP
10 _FB
SLOPE
4
CSLOPE
12
CS
SS
9
CSS
RVCC
DVCC
CVCC
4.7μF
RCS
CCS
L
D3
Q
RS
PGND
V_OUT
18V
COUT
RA
RB
Figure 5. Application Schematic
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:
C_IN
=
4
×
ΔI_L × D
f_OUT × ΔV_Q
ESR = ^ΔVESR
ΔI_L
ΔI_L
=
(V_IN − V_DS) × D
L × f_OUT
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.
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