MP5505 – ENERGY STORAGE AND MANAGEMENT UNIT

MP5505 Rev. 1.01

www.MonolithicPower.com

9

1/12/2015

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© 2015 MPS. All Rights Reserved.

OPERATION

The MP5505 is an energy storage and

management unit in a 3mm×4mm 20-pin QFN

package. It provides very compact and efficient

energy management solution for a typical solid-

state–drive

or

hard-disk–drive

application.

MPS’s patented lossless energy storage and

release

management

circuits

use

a

bi-

directional Buck/Boost converter to achieve

optimal energy transfer and provide the most

cost-effective energy storage solution.

The integrated boost converter raises the

energy-storage voltage level. The storage

feedback resistor divider sets the storage

voltage. When the input suddenly shuts down,

the internal Buck converter transfers the energy

from the storage capacitor to the bus and keep

holds the bus voltage when the system

consumes the energy from the storage

capacitor. The buck converter can work in

100% duty cycle operation to fully deplete the

stored energy.

Start-Up

When VIN starts up, the bus voltage VB is

charged from 0 to nearly VIN. The VB rising

slew rate is controlled by DVDT capacitance.

This function avoids the input inrush current

and provides protection to the whole system.

EHCH is used to enable the storage charge and

release circuitry. When ENCH is already high

before VB finishing DVDT process, the storage

charge circuitry will work automatically when

VIN is higher than UVLO which is 2.5V typically.

The storage charge circuitry operates in two

modes: the pre-charge mode where the STRG

voltage is charged to VB voltage by using a

current source and the boost mode where the

STRG voltage is charged to finally setting

voltage. The pre-charge mode charges the

STRG voltage up to nearly VB voltage by using

almost constant current source. The current is

around 130mA. When STRG voltage is close to

VB, and VB voltage is higher than certain

threshold where the corresponding FBB is

higher than 0.813V, the boost mode initiates.

The boost mode charges the STRG voltage to

the target voltage finally. Figure 2 shows the

charging build-up process when ENCH is high

before VB starts up.

It is strongly recommended for our customers to

enable the ENCH after VB is well settled down

which is shown in Figure 3. Because the

release mode is triggered when FBB voltage is

lower than 0.79V, although there is a 23mV

hysteresis between boost mode and release

mode, in some high current charge boost mode

case which can be programmed by ICH, VB

voltage might be pulled low back and wrongly

enter the release mode. In order to avoid this,

the ENCH pin is suggested to be enabled after

VB settling down. Figure 3 shows the charging

build-up process when ENCH is enabled after

VB settles down.

EN&ENCH

Power ON Delay Time

STRG Pre-Charge Mode

VB

VB Dvdt

Charge Up

STRG Boost Mode

FBB=0.813V

Figure 2: Charging Process

EN

Power ON Delay Time

STRG Pre-Charge Mode

VB

VB Dvdt

Charge Up

ENCH

STRG Boost Mode

Figure.3 Charging Process when EN and ENCH

Separated