MP5505 – ENERGY STORAGE AND MANAGEMENT UNIT

MP5505 Rev. 1.01

www.MonolithicPower.com

10

1/12/2015

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Storage Voltage

After the start up period, the internal Boost

converter automatically regulates the storage

voltage to a set value. The MP5505 uses burst

mode to minimize the converter’s power loss.

When the storage voltage drops below the set

voltage, burst mode initiates and charges the

storage capacitor. During the burst period, the

current limit and the low-side MOSFET control

the switch. When the power MOSFET turns on,

the inductor current increases until it reaches its

current limit. The boost current limit can be

programmable by ICH resistor. By default, it is

around 500mA. After hitting the current limit, the

power MOSFET turns off for the set minimum

OFF time. At the end of this minimum OFF time,

if the feedback voltage remains below the

0.79V internal reference, the power MOSFET

turns on again; otherwise the MP5505 waits

until the voltage drops below the threshold

before turning on the MOSFET.

Release

The MP5505 continuously monitors the input

and bus voltages. Once the bus voltage drops

below the selected release voltage (such as

when losing input power), the internal boost

converter stops charging and works in buck

release mode. In buck mode, the part transfers

energy from the high-voltage storage capacitor

to the low-voltage bus capacitor. Determine the

release voltage by selecting resistor values for

the bus resistor divider. The buck release

current can be as high as 4.5A.

VB

Release VB regulation

voltage

Figure 4: Release Times

The released Buck applies the fixed-frequency

constant-on-time

(COT)

enables

the

fast

transition between charge and release modes.

The buck converter works at 100% duty cycle

until the storage capacitor voltage approaches

the bus voltage. Then the storage and bus

voltages drop until they reach the DC-DC

converter’s UVLO, as shown in Figure 4.

Input-Current Limit

The input-current limiter carefully controls the

input inrush current of the internal hot-swap

MOSFET to prevent an inrush current from the

input to the bus. A capacitor connected to dv/dt

pin can set the soft-start time. Despite of the

soft-start process, the ILIM pin can also limit the

steady-state

current.

Connect

a

resistor

between ILIM and GND to set the current limit.

Reverse-Current Protection

The hot-swapping circuit uses reverse-current

protection to prevent the storage energy from

transferring back to the input during energy

released from storage capacitors to bus. The

hot-swapping MOSFET turns on when input

voltage exceeds the VIN UVLO threshold

during start up, and turn off when input voltage

falls below the bus voltage during release.

Start-Up Sequencing

Connect a capacitor across the DVDT pin to

program the soft-start time. During soft-start,

the energy storage capacitors charge. Very

short dv/dt times can trigger the current-limit

threshold. Select the DVDT capacitor based on

the storage capacity.

When the voltage on the FBS pin (storage

internally pulls the storage PGS pin LOW.

pin goes HIGH.

When the voltage on FBB pin (bus feedback)

LOW to indicate releasing status. When

pulled high to indicate charging status.