MAX15038EVKIT+ Maxim Integrated Products, MAX15038EVKIT+ Datasheet - Page 14

• Manufacturer Part Number: MAX15038EVKIT+
• Description: EVALUATION KIT FOR MAX15038
• Manufacturer: Maxim Integrated Products

Specifications of MAX15038EVKIT+

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.8V
• Current - Output: 4A
• Voltage - Input: 2.9 ~ 5.5V
• Regulator Topology: Buck
• Frequency - Switching: 1MHz
• Board Type: Fully Populated
• Utilized Ic / Part: MAX15038
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

where the output ripple due to output capacitance,
ESR, and ESL is:
or:
or whichever is larger.
The peak-to-peak inductor current (I
Use these equations for initial output capacitor selec-
tion. Determine final values by testing a prototype or an
evaluation circuit. A smaller ripple current results in less
output-voltage ripple. Since the inductor ripple current
is a factor of the inductor value, the output-voltage rip-
ple decreases with larger inductance. Use ceramic
capacitors for low ESR and low ESL at the switching
frequency of the converter. The ripple voltage due to
ESL is negligible when using ceramic capacitors.
Load-transient response depends on the selected out-
put capacitance. During a load transient, the output
instantly changes by ESR x ΔI
troller can respond, the output deviates further,
depending on the inductor and output capacitor val-
ues. After a short time, the controller responds by regu-
lating the output voltage back to its predetermined
value. The controller response time depends on the
closed-loop bandwidth. A higher bandwidth yields a
faster response time, preventing the output from deviat-
ing further from its regulating value. See the Compen-
sation Design section for more details.
The input capacitor reduces the current peaks drawn
from the input power supply and reduces switching
noise in the IC. The total input capacitance must be
equal or greater than the value given by the following
equation to keep the input-ripple voltage within
specification and minimize the high-frequency ripple
current being fed back to the input source:
4A, 2MHz Step-Down Regulator
with Integrated Switches
14
______________________________________________________________________________________
I
V
P P
V
V
V
RIPPLE C
−
RIPPLE ESR
RIPPLE ESL
RIPPLE ESL
C
IN MIN
=
_
V
( )
(
(
(
IN
Input-Capacitor Selection
f
=
S
−
=
)
)
)
8
×
V
=
=
=
D x T x I
OUT
L
x C
V
I
I
t
I
P P
P P
t
P P
OFF
IN RIPPLE
ON
−
−
−
I
P P
OUT
−
S
LOAD
−
x
x ESR
x ESL
x ESL
V
P-P
V
x f
OUT
OUT
IN
. Before the con-
S
) is:
where V
voltage across the input capacitors and is recommended
to be less than 2% of the minimum input voltage. D is
the duty cycle (V
od (1/f
The impedance of the input capacitor at the switching
frequency should be less than that of the input source so
high-frequency switching currents do not pass through
the input source, but are instead shunted through the
input capacitor. The input capacitor must meet the ripple
current requirement imposed by the switching currents.
The RMS input ripple current is given by:
where I
The power transfer function consists of one double pole
and one zero. The double pole is introduced by the
inductor L and the output capacitor C
output capacitor determines the zero. The double pole
and zero frequencies are given as follows:
where R
(DC resistance) and the internal switch resistance,
R
MOSFET) and 31mΩ (high-side MOSFET). R
put load resistance, which is equal to the rated output
voltage divided by the rated output current. ESR is the
total equivalent series resistance of the output capacitor.
If there is more than one output capacitor of the same
type in parallel, the value of the ESR in the above equa-
tion is equal to that of the ESR of a single output capacitor
divided by the total number of output capacitors.
The high switching frequency range of the MAX15038
allows the use of ceramic output capacitors. Since the
ESR of ceramic capacitors is typically very low, the fre-
quency of the associated transfer function zero is higher
than the unity-gain crossover frequency, f
cannot be used to compensate for the double pole creat-
ed by the output filtering inductor and capacitor. The dou-
ble pole produces a gain drop of 40dB/decade and a
phase shift of 180°. The compensation network error
DS(ON)
f
P
1
_
S
LC
I
RIPPLE
RIPPLE
).
L
. A typical value for R
IN-RIPPLE
is equal to the sum of the output inductor’s DCR
=
f
P
2
is the input RMS ripple current.
f
=
Z ESR
_
I
LC
_
LOAD
OUT
is the maximum allowed input ripple
=
/V
2
=
×
IN
π
2π
) and T
x L x C
V
OUT
Compensation Design
x ESR x C
DS(ON)
1
×
S
O
(
V
is the switching peri-
V
IN
IN
1
x
O
⎛
⎜
⎝
O
is 24mΩ (low-side
−
. The ESR of the
R
V
R
C
OUT
O
O
, and the zero
+
O
+
ESR
)
R
is the out-
L
⎞
⎟
⎠