MAX8664EVKIT+ Maxim Integrated Products, MAX8664EVKIT+ Datasheet - Page 20

• Manufacturer Part Number: MAX8664EVKIT+
• Description: KIT EVAL FOR MAX8664
• Manufacturer: Maxim Integrated Products

Specifications of MAX8664EVKIT+

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 2, Non-Isolated
• Voltage - Input: 4.5 ~ 28V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: MAX8664
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Output: -
• Power - Output: -
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Connect a resistor from OSC/EN12 to GND to set the
switching frequency between 100kHz and 1000kHz.
Calculate the resistor value (R10 in Figures 2–5) as follows:
There are several parameters that must be examined
when determining which inductor is to be used. Input
voltage, output voltage, load current, switching fre-
quency, and LIR. LIR is the ratio of inductor-current rip-
ple to maximum DC load current (I
LIR value allows for a smaller inductor, but results in
higher losses and higher output ripple. A good compro-
mise between size and efficiency is an LIR of 0.3. Once
all the parameters are chosen, the inductor value is
determined as follows:
where f
value inductor close to the calculated value. The exact
Low-Cost, Dual-Output, Step-Down
Controller with Fast Transient Response
Figure 6d. Sequencing Startup and Shutdown Waveforms with System Enable 2 Signal
20
______________________________________________________________________________________
S
is the switching frequency. Choose a standard
Setting the Switching Frequency
L
=
R
10
V
IN
=
V
×
OUT
2 24 10
f
S
.
×
×
I
LOAD MAX
×
Design Procedure
(
V
f
S
IN
10
−
(
Inductor Selection
(
V
Hz
OUT
LOAD(MAX)
)
)
( )
×
Ω
)
LIR
). A higher
inductor value is not critical and can be adjusted to make
trade-offs among size, cost, and efficiency. Lower induc-
tor values minimize size and cost, but they also increase
the output ripple and reduce the efficiency due to higher
peak currents. On the other hand, higher inductor values
increase efficiency, but eventually resistive losses due to
extra turns of wire exceed the benefit gained from lower
AC current levels. This is especially true if the inductance
is increased without also increasing the physical size of
the inductor. Find a low-loss inductor having the lowest
possible DC resistance that fits the allotted dimensions.
The chosen inductor’s saturation current rating must
exceed the peak inductor current determined as:
The key selection parameters for the output capacitor
are the actual capacitance value, the equivalent series
resistance (ESR), the equivalent series inductance
(ESL), and the voltage-rating requirements. These
parameters affect the overall stability, output voltage
ripple, and transient response. The output ripple has
three components: variations in the charge stored in
the output capacitor, the voltage drop across the
capacitor’s ESR, and ESL caused by the current into
and out of the capacitor. The maximum output voltage
ripple is estimated as follows:
OFF
ON
I
PEAK
OFF
=
ENABLE
I
ON
CHIP
LOAD MAX
(
V
CC
EXTERNAL
)
+
REF
LIR
2
Output Capacitor
×
I
LOAD MAX
REFIN2
OSC/EN12
(
MAX8664
)