MP2625B – SINGLE CELL SWITCHING CHARGER WITH POWER PATH CONTROL

MP2625B Rev. 1.01

www.MonolithicPower.com

26

1/15/2018

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Selecting the Input Capacitor

The input capacitor C1 from the typical

application circuit absorbs the maximum ripple

current from the PWM converter, which is given

by

MAX

_

IN

TC

MAX

_

IN

TC

MAX

_

CC

MAX

_

RMS

V

)

V

V

(

V

I

I









maximum ripple current is 1A. Select the input

capacitors so that the temperature rise due to

the ripple current does not exceed 10°C. Use

ceramic capacitors with X5R or X7R dielectrics

because

of

their

low

ESR

and

small

temperature coefficients.

For most applications, use a 10µF capacitor.

Besides, usually a small cap with at least 1uF

(C1) from IN to GND is required to be put as

much close as possible to the IC. For the input

voltage is high to 10V, consider the spike when

input insert, select the input capacitors (both the

22uF and 1uF) in 25V rating.

Selecting the Output Capacitor

application circuit is in parallel with the SYS

ripple current and smoothes the output voltage.

Its impedance must be much less than that of

the system load to ensure it properly absorbs

the ripple current.

Use a ceramic capacitor because it has lower

ESR and smaller size that allows us to ignore

the ESR of the output capacitor. Thus, the

output voltage ripple is given by:

SYS

SYS

IN

2

SYS

SYS

S

V

1

V

V

r%

V8 C

f

L













(12)

In order to guarantee the ±0.5% system voltage

accuracy, the maximum output voltage ripple

must not exceed 0.5% (e.g. 0.1%). The

maximum output voltage ripple occurs at the

minimum system voltage and the maximum

input voltage.

The output capacitor can be calculated with

Equation (13):

SYS _ MIN

IN

SYS

2

S

V

1

V

C

8f

L

r







 

(13)

When SYSFB pin is floating, output voltage

ripple is the main concern to select the output

selection guide about the SYS capacitance

selection under typical inputs.

Table 5: SYS Capacitance Selection Guide

NOTE:

7)

For different voltage rating, capacitance will have different DC bias characteristic. Suppose a general condition, capacitance drops

SPEC

SYS

IN

SYS

2

S

V

1

V

C

8f

L

r





  

∆r=0.1%

7)

When SYSFB is

Floating

7)

When SYSFB is

Programmed

Temperature

Characteristic

Package

5V

13.6

20

X5R;X7R

Application

Required

9V

13.3

20

X5R;X7R

Application

Required