Application Notes
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Table 3-1; Input/Output Capacitors
Capacitor Recommendations for the PT5800 &
PT5810 Step-Down Regulator Series
Input Capacitor:
The recommended input capacitance is determined by a
700-mA ripple current rating and the following minimum
capacitance requirements.
PT5800 = 820 F minimum capacitance
PT5810 = 1000 F minimum capacitance
Ripple current and <100 m
equivalent series resistance
(ESR) values are the major considerations, along with
temperature, when designing with different types of
capacitors. Tantalum capacitors have a recommended
minimum voltage rating of twice the maximum DC
voltage + AC ripple. This is necessary to ensure reliabil-
ity for input voltage bus applications
Output Capacitors
The ESR of the capacitors is less than 100m
. Electrolytic
capacitors have marginal ripple performance at frequen-
cies greater than 400 kHz, but excellent low frequency
transient response. Above the ripple frequency ceramic
capacitors are necessary. Ceramic capacitors improve the
transient response and reduce any high frequency noise
components apparent during high current excursions.
Preferred low-ESR electrolytic capacitor part numbers
are identified in Table 3-1.
PT5800/5810 Series
Tantalum Capacitors (Optional Output Capacitors)
Tantalum type capacitors can be used for the output but
only the AVX TPS series, Sprague 593D/594/595 series,
or Kemet T495/T510 series. These capacitors are rec-
ommended 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 determining power dissipation capa-
bility. Tantalum or Oscon types are recommended for
applications where ambient temperatures fall below 0°C.
Capacitor Table
Table 2-1 identifies the characteristics of capacitors from a
number of vendors with acceptable ESR and ripple current
(rms) 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 100 kHz are critical param-
eters necessary to insure both optimum regulator performance
and long capacitor life.
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