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Application Notes
Table 1: Input/Output Capacitors
(1) N/R –Not recommended. The surge and normal voltage rating does not meet the minimum operating limits.
Capacitor Recommendations for
the
PT5540 Boost Regulator Regulator Series
Input Capacitors:
The minimum input capacitance required is 100F, with
a 200-mA(rms) ripple current rating and 150m
typical
equivalent series resistance (ESR). Electrolytic capacitors
have marginal ripple performance at frequencies greater
than 400kHz but have excellent low-frequency transient
response. Above the ripple frequency, ceramic capacitors
are necessary to improve the transient response and reduce
any high frequency noise components apparent during
higher current excursions. Preferred ESR type capacitor
part numbers are identified in Table 2-1.
Output Capacitor:
The recommended output capacitance is determined by
0.5-A(rms) ripple current rating and 100F minimum
capacitance. The maximum output capacitance is 560F.
Ripple current and >50m
ESR value are the major
considerations, along with temperature, when designing
with different types of capacitors. Tantalum capacitors
have a recommended minimum voltage rating of 2
× (the
maximum DC voltage + AC ripple). This is necessary to
insure reliability for input voltage bus applications.
PT5540 Series
Tantalum Capacitors (Optional Input Capacitors)
Tantalum type capacitors can be used for the input bus
but only the AVX TPS, Sprague 593D/594/595, or Kemet
T495/T510 series. These capacitors are recommended
over many other tantalum types due to their higher rated
surge, power dissipation, and ripple current capability.
As a caution the TAJ series by AVX is not recommended.
This series has considerably higher ESR, reduced power
dissipation, and lower ripple current capability. The TAJ
series is less reliable than the AVX TPS series when deter-
mining power dissipation capability. Tantalum or Oscon
types are recommended for applications where ambient
temperatures fall below 0°C. Do not use tantalum capaci-
tors on the output bus.
Capacitor Table
Table 1 identifies the characteristics of capacitors from a
number of vendors with acceptable ESR and ripple current
ratings. The number of capacitors required at both the
input and output buses is identified for each capacitor type.
This is not an extensive capacitor list. Capacitors from other
vendors are available with comparable specifications. Those listed
are for guidance. The RMS ripple current rating and ESR
(Equivalent Series Resistance at 100kHz) are critical parameters
necessary to insure both optimum regulator performance and
long capacitor life.
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