MAX17014EVKIT+ Maxim Integrated Products, MAX17014EVKIT+ Datasheet - Page 27

• Manufacturer Part Number: MAX17014EVKIT+
• Description: KIT EVAL FOR MAX17014
• Manufacturer: Maxim Integrated Products

Specifications of MAX17014EVKIT+

• Main Purpose: Special Purpose DC/DC, LCD Supply
• Outputs And Type: 4, Non-Isolated
• Power - Output: 32.9W
• Voltage - Output: 3.3V, 16V, -6V, 35V
• Current - Output: 2A, 1.5A, 100mA, 50mA
• Voltage - Input: 10.8 ~ 13.2V
• Regulator Topology: Boost, Buck
• Frequency - Switching: 1.2MHz
• Board Type: Fully Populated
• Utilized Ic / Part: MAX17014
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The worst case is I
V
For most applications, ceramic capacitors are used
because of their high ripple current and surge current
capabilities. For optimal circuit long-term reliability,
choose an input capacitor that exhibits less than +10°C
temperature rise at the RMS input current corresponding
to the maximum load current.
Since the MAX17014’s step-down regulator is internally
compensated, it is stable with any reasonable amount
of output capacitance. However, the actual capacitance
and equivalent series resistance (ESR) affect the regu-
lator’s output ripple voltage and transient response. The
rest of this section deals with how to determine the out-
put capacitance and ESR needs according to the
ripple-voltage and load-transient requirements.
The output voltage ripple has two components: varia-
tions in the charge stored in the output capacitor, and
the voltage drop across the capacitor’s ESR caused by
the current into and out of the capacitor:
where I
of the Step-Down Regulator section, C
capacitance, and R
capacitor C
current is 0.77A. If the voltage-ripple requirement of
Figure 1’s circuit is ±1% of the 3.3V output, then the
total peak-to-peak ripple voltage should be less than
66mV. Assuming that the ESR ripple and the capacitive
ripple each should be less than 50% of the total peak-
to-peak ripple, then the ESR should be less than 43mΩ
and the output capacitance should be more than 2.43µF
to meet the total ripple requirement. A 22µF capacitor
with ESR (including PCB trace resistance) of 10mΩ is
selected for the standard application circuit in Figure 1,
which easily meets the voltage-ripple requirement.
The step-down regulator’s output capacitor and ESR can
also affect the voltage undershoot and overshoot when
the load steps up and down abruptly. The step-down
regulator’s transient response is typically dominated by
its loop response and the time constant of its internal
integrator. However, excessive inductance or insufficient
output capacitance can degrade the natural transient
VIN
V
OUT RIPPLE
= 2 x V
V
OUT RIPPLE ESR
OUT
_
_
V
_
OUT
OUT
OUT RIPPLE C
RIPPLE
. In Figure 1’s circuit, the inductor ripple
.
=
_
V
______________________________________________________________________________________
(
OUT RIPPLE ESR
RMS
is defined in the Inductor Selection
ESR
)
_
=
( )
_
= 0.5 x I
I
OUT
OUT RIPPLE
Output Capacitor Selection
=
8
_
I
is the ESR of the output
(
OUT RIPPLE
×
C
OUT
OUT
)
_
+
, which occurs at
V
×
OUT
×
OUT RIPPLE C
R
f
SW
ESR OUT
is the output
_
_
( )
Power Supply for LCD TVs
Low-Cost Multiple-Output
response. Calculating the ideal transient response of
the inductor and capacitor, which assumes an ideal
response from the regulator, can ensure that these
components do not degrade the IC’s natural response.
The ideal undershoot and overshoot have two compo-
nents: the voltage steps caused by ESR, and the voltage
sag and soar due to the finite capacitance and the induc-
tor current slew rate. Use the following formulas to check
if the ESR is low enough and the output capacitance is
large enough to prevent excessive soar and sag.
The amplitude of the ESR step is a function of the load
step and the ESR of the output capacitor:
The amplitude of the capacitive sag is a function of the
load step, the output capacitor value, the inductor
value, the input-to-output voltage differential, and the
maximum duty cycle:
The amplitude of the capacitive soar is a function of the
load step, the output capacitor value, the inductor
value, and the output voltage:
Keeping the full-load overshoot and undershoot less
than 3% ensures that the step-down regulator’s natural
integrator response dominates. Given the component
values in the circuit of Figure 1 and assuming a full 2A
step load transient, the voltage step due to capacitor
ESR is negligible. The voltage sag and soar are 44.3mV
and 71.6mV, or a little over 1% and 2%, respectively.
The MAX17014’s high switching frequency demands a
high-speed rectifier. Schottky diodes are recommended
for most applications because of their fast recovery time
and low forward voltage. In general, a 2A Schottky diode
works well in the MAX17014’s step-down regulator.
The inductance value, peak current rating, and series
resistance are factors to consider when selecting the
inductor. These factors influence the converter’s effi-
ciency, maximum output load capability, transient
response time, and output voltage ripple. Physical size
and cost are also important factors to be considered.
V
OUT SAG
_
V
OUT ESR STEP
V
OUT SOAR
=
_
2
×
_
C
_
OUT
=
×
L
=
L
2
(
OUT
V
OUT
Δ
×
VIN MIN
I
C
OUT
OUT
(
×
Step-Up Regulator
×
(
(
Δ
×
Δ
I
)
R
×
Inductor Selection
OUT
I
OUT
×
ESR OUT
V
D
OUT
Rectifier Diode
MAX
)
)
_
2
2
−
V
OUT
)
27