MAX15005 Maxim Integrated Products, MAX15005 Datasheet - Page 15

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

www.DataSheet.co.kr
When the voltage produced by this current (through the
current-sense resistor) exceeds the current-limit com-
parator threshold, the MOSFET driver (OUT) quickly ter-
minates the on-cycle. In most cases, a short-time
constant RC filter is required to filter out the leading-
edge spike on the sense waveform. The amplitude and
width of the leading edge depends on the gate capaci-
tance, drain capacitance (including interwinding capac-
itance), and switching speed (MOSFET turn-on time).
Set the RC time constant just long enough to suppress
the leading edge. For a given design, measure the lead-
ing spike at the highest input and rated output load to
determine the value of the RC filter.
The low 305mV current-limit threshold reduces the
power dissipation in the current-sense resistor. The cur-
rent-limit threshold can be further reduced by adding
an offset to the CS input from REG5 voltage. Do not
reduce the current-limit threshold below 150mV as it
may cause noise issues. See Figure 4. For a new value
of the current-limit threshold (V
value of R1 using the following equation.
Figure 4. Reducing Current-Sense Threshold
Flyback/Boost/SEPIC Power-Supply Controllers
CURRENT-LIMIT
MAX15004A/B
MAX15005A/B
COMPARATOR
R
1
______________________________________________________________________________________
=
0 290
.
0.3V
4 75
REG5
.
−
V
×
CS
R
CS-LOW
CS
−
R1
C
Low
CS
R
CS
), calculate the
4.5V to 40V Input Automotive
V
IN
N
R
S
The MAX15004A/B/MAX15005A/B can be configured
for step-up conversion. The boost converter output can
be fed back to V
can function even during cold-crank input voltage
(≤ 2.5V). Use a Schottky diode (D
avoid backfeeding the input source. A current-limiting
resistor (R
output to V
put voltage. The total current sink into V
ited to 30mA. Use the equations in the following
sections to calculate R
capacitor (C
using the converter in boost operation.
Using the following equation, calculate the minimum
inductor value so that the converter remains in continu-
ous mode operation at minimum output current (I
where:
and
The higher value of I
tance; however, it increases the peak and RMS currents
in the switching MOSFET and inductor. Use I
10% to 25% of the full load current. The V
ward voltage drop of the external Schottky diode, D is
the duty cycle, and V
external switch. Select the inductor with low DC resis-
tance and with a saturation current (I
than the peak switch current limit of the converter.
VCC
CC
Inductor Selection in Boost Configuration
L
I
OMIN
MIN
IN
) is also needed from the boost converter
depending upon the boost converter out-
), and output capacitor (C
Applications Information
CC
D
=
=
=
2 f
(see Figure 5) so that the controller
×
OMIN
V V
(0.1 I ) to (0.25 I
V
DS
OUT
OUT
OUT
is the voltage drop across the
VCC
V
×
IN
reduces the required induc-
+
+
O
×
2
V
V
, inductor (L
V
D
×
D
OUT
D
−
−
VIN
V
Boost Converter
×
V
DS
IN
×
η
) in the V
SAT
I
OMIN
×
CC
) rating higher
O
must be lim-
)
D
MIN
OUT
OMIN
is the for-
IN
), input
) when
path to
OMIN
from
15
).
Datasheet pdf - http://www.DataSheet4U.net/