MAX15035 Maxim Integrated Products, MAX15035 Datasheet - Page 21

• Manufacturer Part Number: MAX15035
• Description: 15A Step-Down Regulator
• Manufacturer: Maxim Integrated Products

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Including an additional resistor between ILIM and the
output automatically creates a current-limit threshold that
folds back as the output voltage drops (see Figure 8).
The foldback current limit helps limit the inductor current
under fault conditions, but must be carefully designed to
provide reliable performance under normal conditions.
The current-limit threshold must not be set too low, or the
controller will not reliably power up. To ensure the con-
troller powers up properly, the minimum current-limit
threshold (when V
the maximum load during startup (which at least consists
of leakage currents), plus the maximum current required
to charge the output capacitors:
The output filter capacitor must have low enough equiv-
alent series resistance (ESR) to meet output ripple and
load-transient requirements. Additionally, the ESR
impacts stability requirements. Capacitors with a high
ESR value (polymers/tantalums) do not need additional
external compensation components.
Figure 8. Standard Application with Foldback Current-Limit Protection
15A Step-Down Regulator with Internal Switches
I
START
LO
AGND
GND/OPEN/REF/V
HI
= C
5V BIAS
SUPPLY
OUT
OUT
______________________________________________________________________________________
ON
97.6kΩ
Output Capacitor Selection
R3
AGND
AGND
= 0V) must always be greater than
AGND
OFF
x 1mV/µs + I
DD
1000pF
54.9kΩ
1µF
C2
C3
Foldback Current Limit
49.9kΩ
100kΩ
R2
1µF
R10
C1
R1
PWR
LOAD(START)
37
38
36
34
35
4
2
3, 28, EP1
PGOOD
EN
REF
V
V
SKIP
REFIN
PWR
DD
CC
MAX15035
AGND
AGND
PGND
ILIM
TON
BST
LX
FB
IN
29
18–26, EP3
6–15
32
33
30
5, 16, EP2
In core and chipset converters and other applications
where the output is subject to large-load transients, the
output capacitor’s size typically depends on how much
ESR is needed to prevent the output from dipping too
low under a load transient. Ignoring the sag due to
finite capacitance:
In low-power applications, the output capacitor’s size
often depends on how much ESR is needed to maintain
an acceptable level of output ripple voltage. The output
ripple voltage of a step-down controller equals the total
inductor ripple current multiplied by the output capaci-
tor’s ESR. The maximum ESR to meet ripple require-
ments is:
where f
200kΩ
PWR
R
TON
R8
100kΩ
R5
49.4kΩ
AGND
49.9kΩ
SW
R4
C
0.1µF
is the switching frequency.
R
BST
ESR
(
R
REF
ESR
≤
L1
⎡
⎢
⎢
⎣
(
+
V
IN
R
V
PCB
IN
−
SEE TABLE 1 FOR COMPONENT SELECTION.
V
×
OUT
)
f
SW
≤
∆
)
PWR
C
C
PWR
×
I
OUT
V
IN
LOAD MAX
L
OUT
V
STEP
7V TO 24V
(
⎤
⎥
⎥
⎦
1.50V 10A
INPUT
V
1.05V 7A
OUTPUT
RIPPLE
)
21
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