MP111 View Datasheet(PDF) - Monolithic Power Systems
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MP111 Datasheet PDF : 13 Pages
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MP111 – DYING GASP STORAGE AND RELEASE CONTROL IC
application. Assume the input release current is
IRELEASE when input voltage is regulated at
VRELEASE for the DCDC converter. The storage
voltage of MP111 is VSTORAGE, and the required
dying gasp time is TDASP. The necessary storage
capacitance can be calculated as following
equation:
Cs
IRELEASE TDASP
V V STORAGE
RELEASE
If IRELEASE=1A, TD=20ms, VSTORAGE=20V,
VRELEASE=10V, the needed storage capacitance is
2000μF. Generally, the storage capacitance
should be chosen a little bit large to avoid
capacitance reduction at high voltage offset.
In typical xDSL applications using a 12V input
supply, it is recommended to set the storage
voltage higher than 20V to fully utilize the high
voltage energy and minimize storage
capacitance requirements. Generally, a 25V
rated electrolytic capacitor can be used. The
lifetime of electrolytic capacitors can be severely
impacted by both environmental and electrical
factors. One of the most critical electrical factors
is the AC RMS ripple current through the
capacitor which leads to increased capacitor core
temperatures. Normally, for typical industrial uses,
it is recommended to derate the capacitor voltage
rating by as much as 70%-80%. For example, a
25V rated electrolytic capacitor would be used for
a 16V to 20V application.
However, since the MP111 tightly regulates the
storage voltage, the storage capacitor almost has
no AC ripple current going through it. The
resulting refresh rate of the MP111 is very low
which allows customers to safely use a 90%
capacitor derating (6). For example, a 25V
electrolytic capacitor, can safely handle a storage
voltage of up to 22V. Table 3 is some
recommended storage electrolytic capacitors
which can be used in typical xDSL application
PCB Layout Guide
PCB layout is very important to achieve stable
operation. Please follow these guidelines and
take the EVB board layout for references.
1) Connect the BST pin as close as possible to
the SW node of DCDC converter through a
resistor and a small ceramic capacitor. Try to
avoid interconnect the feedback path.
2) Ensure all feedback connections are short
and direct. Place the feedback resistors and
compensation components as close to the
chip as possible.
3) Keep the connection of the storage
capacitors and STRG pin as short and wide
as possible.
Table 3 – Recommended Storage Capacitors
Part #
Vender
Capacitance
Voltage Operating Temp
25ME1500WX
PEH526HAB4270M3
EEUFR1E152B
Sanyo
Kemet
Panasonic
1500μF
2700μF
1500μF
25V
-40 to +105C
25V
-40 to +105C
25V
-40 to +105C
Notes:
6) “Applying voltage does not affect the life time because the self heating by applying voltage can be ignored”, from Sanyo.
MP111 Rev. 1.0 1
www.MonolithicPower.com
11
4/25/2018
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