MP111 – DYING GASP STORAGE AND RELEASE CONTROL IC

MP111 Rev. 1.0 1

www.MonolithicPower.com

11

4/25/2018

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2018 MPS. All Rights Reserved.

application. Assume the input release current is

capacitance can be calculated as following

equation:

RELEASE

DASP

STORAGE

RELEASE

IT

Cs

VV







If

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%

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

Sanyo

1500μF

25V

-40 to +105

C

PEH526HAB4270M3

Kemet

2700μF

25V

-40 to +105

C

EEUFR1E152B

Panasonic

1500μF

25V

-40 to +105

C

Notes:

6) “Applying voltage does not affect the life time because the self heating by applying voltage can be ignored”, from Sanyo.