MP5505A

– ENERGY STORAGE AND MANAGEMENT UNIT

MP5505A Rev. 1.1

www.MonolithicPower.com

12

12/13/2016

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

© 2016 MPS. All Rights Reserved.

APPLICATION INFORMATION

Selecting Input Capacitor and TVS

Capacitors at VIN are recommended to absorb

possible voltage spikes during input-power turn

on, input-switch hard off (during power off), or

other

special

conditions.

The

application

determines the capacitor. For example, if the

input-power

trace

is too

long

(with

higher

parasitic inductance) during the input-switch

hard-off period, more energy pumps into the

input. This means more input capacitors are

needed to ensure the input voltage spike stays in

a safe range. Use a 0.1uF (or larger) capacitor

based on the spike condition.

Keep inrush-current requirements in mind when

selecting an input capacitor. Typically, more input

capacitors result in a higher input-inrush current

during hot-plugging. A smaller input capacitor is

needed for a smaller inrush current. MP5505A

works normally with a very small input capacitor.

However, this leads to a possible high-voltage

spike. An efficient solution is to add a TVS diode

at the input to absorb the possible input-voltage

spike. At the same time, keep the inrush current

small during hot-plugging. A typical TVS diode,

like SMA6J5.0A, is recommended.

Setting the Storage Voltage

Set the storage voltage by choosing the external

feedback resistors R11 and R12 shown in Figure

5.

Figure 5. Storage Feedback Circuit

The storage voltage is determined by:

STORAGE

FBS

R11

V

(1

) V

R12

 



not critical for normal operation. Select R11 and

R12

higher than 10kΩ to account for the bleed

current. For example, if R12 is 14k

Ω, R11 is then:

STORAGE

FBS

FBS

14k

(V

V

)

R11

V







For a 12V storage voltage, R11 is 200k

Ω.

Table 1 lists the recommended resistors for

different storage voltages.

R11 (k

Ω)

R12 (k

Ω)

8

127

14

12

200

14

20

340

14

Select Release Voltage and VBus Capacitors

Select the release voltage by choosing the

external feedback resistors R1 and R2 (see

Figure 6).

Similarly, the release voltage is:

RELEASE

FBB

R1

V

(1

) V

R2

 



only determine the release voltage, but also

affect stability. Since the release-buck mode

works in COT mode, avoid small resistor values

to ensure a sufficient voltage ramp. Generally,

choose R1//R2

≥20kΩ for stable performance with

values for different release voltages.

Figure 6. Release Feedback Circuit

R1 (k

Ω)

R2 (k

Ω)

4.2

105

24.3

2.9

107

40.2

Selecting the Storage Capacitor

The storage capacitor stores energy during

normal operation and releases this energy to VB