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ATH30T05 Datasheet(PDF) 5 Page - Astec America, Inc

Part No. ATH30T05
Description  30-A, 5-V Input Non-Isolated Wide-Output Adjust Power Modules
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Maker  ASTEC [Astec America, Inc]
Homepage  http://www.astecinc.com/
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ATH30T05 Datasheet(HTML) 5 Page - Astec America, Inc

 
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Application Notes
North America (USA): 1-888-41-ASTEC
Europe (UK): 44(1384)842-211
Asia (HK): 852-2437-9662
ATH30T033 & ATH30T05 Series
Capacitor Recommendations for
the ATH30T033 &
ATH30T05 Series of Power Modules
Input Capacitor
The recommended input capacitor(s) is determined by
the 1,500 µF (1) minimum capacitance and 900 mArms
minimum ripple current rating.
Ripple current and <100 m
Ω equivalent series resistance
(ESR) values are the major considerations, along with
temperature, when designing with different types of
capacitors. Unlike polymer tantalum, conventional tan-
talum capacitors have a recommended minimum voltage
rating of 2
× (maximum DC voltage + AC ripple). This
is standard practice to ensure reliability.
For improved ripple reduction on the input bus, ceramic
capacitors may be used to complement electrolytic types
and achieve the minimum required capacitance.
Output Capacitors (Optional)
For applications with load transients (sudden changes in
load current), regulator response will benefit from an
external output capacitance. The recommended output
capacitance of 330 µF will allow the module to meet
its transient response specification (see product data sheet).
For most applications, a high quality computer-grade
aluminum electrolytic capacitor is most suitable. These
capacitors provide adequate decoupling over the frequency
range, 2 kHz to 150 kHz, and are suitable when ambient
temperatures are above 0 °C. For operation below 0 °C,
tantalum, ceramic or Os-Con type capacitors are recom-
mended. When using one or more non-ceramic capacitors,
the calculated equivalent ESR should be no lower than
4 m
Ω (7 mΩ using the manufacturer’s maximum ESR
for a single capacitor). A list of preferred low-ESR type
capacitors are identified in Table 1-1.
Ceramic Capacitors
Above 150 kHz the performance of aluminum electrolytic
capacitors becomes less effective. To further improve the
reflected input ripple current or the output transient
response, multilayer ceramic capacitors can also be added.
Ceramic capacitors have very low ESR and their resonant
frequency is higher than the bandwidth of the regulator.
When used on the output their combined ESR is not
critical as long as the total value of ceramic capacitance
does not exceed 300 µF. Also, to prevent the formation of
local resonances, do not place more than five identical ce-
ramic capacitors in parallel with values of 10 µF or greater.
Tantalum Capacitors
Tantalum type capacitors can be used at both the input
and output, and are recommended for applications where
the ambient operating temperature can be less than 0 °C.
The AVX TPS, Sprague 593D/594/595 and Kemet T495/
T510 capacitor series are suggested over many other
tantalum types due to their higher rated surge, power
dissipation, and ripple current capability. As a caution
many general purpose tantalum capacitors have consider-
ably higher ESR, reduced power dissipation and lower
ripple current capability. These capacitors are also less
reliable when determining their power dissipation and
surge current capability. Tantalum capacitors that do
not have a stated ESR or surge current rating are not
recommended for power applications.
When specifying Os-Con and polymer tantalum capacitors
for the output, the minimum ESR limit will be encoun-
tered well before the maximum capacitance value is
reached.
Capacitor Table
Table 1-1 identifies the characteristics of capacitors from a
number of vendors with acceptable ESR and ripple current
(rms) ratings. The recommended 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 (at 100kHz) are critical parameters necessary to insure
both optimum regulator performance and long capacitor life.
Designing for Very Fast Load Transients
The transient response of the DC/DC converter has been
characterized using a load transient with a di/dt of 1 A/µs.
The typical voltage deviation for this load transient is
given in the data sheet specification table using the
optional value of output capacitance. As the di/dt of a
transient is increased, the response of a converter’s regu-
lation circuit ultimately depends on its output capacitor
decoupling network. This is an inherent limitation with
any DC/DC converter once the speed of the transient
exceeds its bandwidth capability. If the target application
specifies a higher di/dt or lower voltage deviation, the
requirement can only be met with additional output
capacitor decoupling. In these cases special attention
must be paid to the type, value and ESR of the capacitors
selected.
If the transient performance requirements exceed that
specified in the data sheet, or the total amount of load
capacitance is above 3,000 µF, the selection of output
capacitors becomes more important. For further guidance
consult the separate application note, “Selecting Capaci-
tors for PTH Products in High-Performance Applications.”


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