MP5512 – 18V, 4.5A ENERGY STORAGE AND MANAGEMENT UNIT

MP5512 Rev. 1.1

www.MonolithicPower.com

17

4/27/2016

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© 2016 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Storage Voltage

Set the storage voltage by choosing the

external feedback resistors R5 and R6 (see

Figure 5)..

Figure 5: Storage Feedback Circuit

The storage voltage is determined by:

STORAGE

FBS REF

R5

V(1

) V

R6







not critical for normal operation. Select an R6

resistor higher than 10kΩ to reduce the bleed

current and lower than 50kΩ to enhance noise

immunity. For example, if R6 is 10kΩ, R5 is

calculated as:

REF

FBS

REF

FBS

STORAGE

V

V

V

k

R













)

(

10

5

For a 24V storage voltage, R5 is 290kΩ.

Table 1 lists the recommended feedback

resistance for different storage voltages.

R5 (kΩ)

R6 (kΩ)

12

140

10

24

290

10

40

490

10

Setting VIN Power-Failure Threshold Voltage

and VB Release-Regulation Voltage

Set the release-trigger voltage by choosing the

external feedback resistors R1 and R2 (see

Figure 6). Release-trigger voltage is determined

The input power-failure release threshold is:

V

R

R

V

PFI

792

.

0

)

2

1

1

(







R1

R2

VIN

DET

C1

Figure 6: Release-Feedback Circuit

(see Figure 7).

R3

R4

VB

FBB

C2

Figure 7: VB Regulation Feedback Circuit

The bus-regulation voltage can be calculated by:

)

2

(

)

4

3

1

(

RAMP

REF

FBB

RLS

V

V

R

R

VB











Where,

is

buck

FBB

internal

compensation ramp voltage, and can be

estimated as:

)

220

10

)

1

(

6

SW

STRG

RAMP

F

D

D

V

V













R3 and R4 are related to buck-release stability.

Since the release-buck mode works in COT

mode, try to avoid small resistor values that

affect the internal voltage ramp. Generally,

choose R3//R4≥10kΩ for stable performance

Selecting the Storage Capacitor

The storage capacitor stores energy during

normal operation and releases this energy to

VB when VIN loses input power. Use a general-