MCP16301_15 Datasheet, PDF (18/40 Pages) Microchip Technology – High-Voltage Input Integrated Switch Step-Down Regulator

MCP16301/H
5.4 Input Capacitor Selection
The step-down converter input capacitor must filter the
high input ripple current as a result of pulsing or
chopping the input voltage. The input voltage pin of the
MCP16301/H devices is used to supply voltage for the
power train and as a source for internal bias. A low
equivalent series resistance (ESR), preferably a
ceramic capacitor, is recommended. The necessary
capacitance is dependent upon the maximum load
current and source impedance. Three capacitor
parameters to keep in mind are the voltage rating,
equivalent series resistance and the temperature
rating. For wide temperature range applications, a
multi-layer X7R dielectric is mandatory, while for
applications with limited temperature range, a
multi-layer X5R dielectric is acceptable. Typically, input
capacitance between 4.7 µF and 10 µF is sufficient for
most applications. For applications with 100 mA to
200 mA load, a 1 µF X7R capacitor can be used,
depending on the input source and its impedance.
The input capacitor voltage rating should be a minimum
of V_IN plus margin. Table 5-2 contains the
recommended range for the input capacitor value.
5.5 Output Capacitor Selection
The output capacitor helps in providing a stable output
voltage during sudden load transients, and reduces the
output voltage ripple. As with the input capacitor, X5R
and X7R ceramic capacitors are well suited for this
application.
The MCP16301/H devices are internally compensated,
so the output capacitance range is limited. See
Table 5-2 for the recommended output capacitor range.
The amount and type of output capacitance and
equivalent series resistance will have a significant
effect on the output ripple voltage and system stability.
The range of the output capacitance is limited due to
the integrated compensation of the MCP16301/H
devices.
The output voltage capacitor voltage rating should be a
minimum of V_OUT, plus margin.
Table 5-2 contains the recommended range for the
input and output capacitor value:
TABLE 5-2:
Parameter
C_IN
C_OUT
CAPACITOR VALUE RANGE
Min
Max
2.2 µF
20 µF
none
none
5.6 Inductor Selection
The MCP16301/H devices are designed to be used
with small surface mount inductors. Several
specifications should be considered prior to selecting
an inductor. To optimize system performance, the
inductance value is determined by the output voltage
(Table 5-1) so the inductor ripple current is somewhat
constant over the output voltage range.
EQUATION 5-4: INDUCTOR RIPPLE
CURRENT
_IL = -V-L--^L-  t_ON
EXAMPLE 5-3:
V_IN = 12V
V_OUT = 3.3V
I_OUT = 600 mA
EQUATION 5-5: INDUCTOR PEAK
CURRENT
I_LPK = ^---2--I--^L- + I_OUT
Inductor ripple current = 319 mA
Inductor peak current = 760 mA
An inductor saturation rating minimum of 760 mA is
recommended. Low ESR inductors result in higher
system efficiency. A trade-off between size, cost and
efficiency is made to achieve the desired results.
DS20005004D-page 18
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