MP5505 – ENERGY STORAGE AND MANAGEMENT UNIT

MP5505 Rev. 1.01

www.MonolithicPower.com

12

1/12/2015

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Consider of the power loss during releasing

where the Buck converter can run up to 90%

efficiency in most application, select storage

capacitance to 1.1xCs to ensure enough

storage capacitance is 1500μF.

For typical applications using a 5V input supply,

set the storage voltage above 10V to fully utilize

the high-voltage energy and minimize the storage

capacitance requirements. Generally, use the

16V POS capacitor or 25V electrolytic capacitors.

Selecting the External Diode

The external diode is strongly recommended for

normal operation of charge mode where the

boost converter works. The voltage rating should

be higher than the storage voltage and the

current rating should be high than the current

programmed by ICH pin.

Setting the Input Hot-Swap Current Limit

Connect a resistor from ILIM to GND to set the

current limit value. For example, a 1.2kΩ resistor

sets the current limit to about 4.1A. Table 3 lists

the recommended resistors for different current

limit values.

4.6

1.07

4.1

1.2

3.7

1.4

1.6

3.2

Selecting Inductor

The inductor is necessary to supply constant

current to the load. Since the Boost mode and

Buck mode are sharing the same inductor, and

generally the Buck mode current is higher, the

inductor supporting at least the Buck mode

releasing current is recommended.

Selecting the inductor based on Buck releasing

mode. If the storage voltage is VS, the release

voltage is VR, and Buck running at fixed 500kHz

frequency. The inductance

value

can

be

calculated by:

RR

LSW

S

VV

L(1

)

IF

V

=× −

Δ×

current which can be set in the range of 30% to

40% of full releasing current.

The inductor should not saturate under the

maximum inductor peak current.

Setting the Power-On Reset Delay Time

Connect a capacitor to the TPOR pin to set the

power on reset delay time. Leave it floating for

the default delay time of around 0.4ms. Table 4

lists the recommended capacitors for different

delay times. In order to eliminate the power on

reset delay, connect the TPOR pin directly to VIN.

Table 4: Reset Delay vs. Capacitor Value

100

100

500

500

Setting the Bus Voltage Rise Time

Connect a capacitor to the DVDT to set the bus

voltage start-up slew rate and soft-start time.

Leave it floating for the default soft start time of

around 0.9ms from 0V to 5V. Table 5 lists the

recommended capacitors for different soft-start

times.

Table 5: Soft-Start vs. Capacitor Value

10

10

100

100

Layout Recommendation

1) The high current paths (VIN, VB, VBO,

SW, STRG, GND) should use short, wide

and direct traces.

2) Put the decoupling capacitor across VB

and GND as close as possible.

3) Put the decoupling capacitor across

STRG and GND as close as possible.

4) Keep the switching node SW short and

away from the feedback network.

5) The external feedback resistors should be

placed next to FB pins.

6) Keep the BST voltage path (BST, C6, R5

and SW) as short as possible.

7) Four-layout is recommended to achieve

better thermal performance and easily

layout.