MP5505E – ENERGY STORAGE AND MANAGEMENT UNIT

MP5505E Rev. 1.01

www.MonolithicPower.com

12

5/15/2020

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

© 2020 MPS. All Rights Reserved.

MOSFET (LS-FET) control the switch. When

the LS-FET turns on, the inductor current

increases until it reaches its current limit. The

boost current limit can be programmed by a 68

- 200kΩ ICH resistor. After reaching the current

limit, the LS-FET turns off for the set minimum

off time. At the end of this minimum off time, if

the feedback voltage remains below the 0.795V

internal reference, the LS-FET turns on again.

Otherwise, the MP5505E waits until the voltage

drops below the threshold before turning on the

LS-FET.

Release

The MP5505E monitors the input and bus

voltages continuously. 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 released buck applies a fixed-frequency

constant-on-time (COT) control and enables a

fast transition between the 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 (see Figure 4).

VB

VSTRG

PGIN

Release VB Regulation

Voltage

Figure 4: Release Times

During the buck release mode, if the load is too

high and the buck switching peak current limit is

triggered, the MP5505E prolongs the HS-FET

off period. This way, the inductor current can

ramp down in each cycle and prevent a

switching current runaway.

Input Current Limit

The input current limiter controls the input

inrush current of the internal hot-swap MOSFET

carefully to prevent inrush current from the input

to the bus. A capacitor connected to dV/dt sets

the soft-start time. Despite the soft-start

process, ILIM can 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 when the energy

is released from the storage capacitors to the

bus. The hot-swap MOSFET turns on when the

input voltage exceeds the VIN UVLO threshold

during start-up (or when the input voltage is

about 0.2V higher than the VB voltage). The

hot-swap MOSFET turns off when the input

voltage falls below the bus voltage during

release (or the input falls below the PGIN

threshold).

Start-Up Sequencing

Connect a capacitor across DVDT to program

the

soft-start

time.

The

energy

storage

capacitors charge during the soft start. Very

short dV/dt times can trigger the current-limit

threshold. Select a DVDT capacitor based on

the storage capacity.

Storage Power-Good Indicator (PGS)

When the voltage on the storage feedback

(FBS) drops below 0.9 x VFBS, the MP5505E

pulls PGS low internally. When the FBS voltage

is above 0.95 x VFBS, PGS goes high.

Bus Power-Good Indicator (PGIN)

When the voltage on the bus feedback (FBB)

falls below 1.0 x VFBB, the MP5505E pulls PGIN

low to indicate the release status. When the

MP5505E works in boost mode, PGIN is pulled

high to indicate the charging status.