MP5403

– CONFIGURABLE 2.7V-6V MINI PMIC WITH DUAL 2.5A/3.5A BUCK,

ONE LOAD SWITCH, AND INPUT POWER SUPERVISORY

MP5403 Rev. 1.0

www.MonolithicPower.com

19

9/20/2016

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

© 2016 MPS. All Rights Reserved.

APPLICATION INFORMATION

Output Voltage Setting

The output voltage of the two switchers can be

adjusted with external resistor dividers (see

Figure 5). The typical reference voltage of both

FB1 and FB2 is 600mV. The maximum allowed

voltage for the outputs is close to the input

voltage minus the voltage drop when the high-

side switch is 100% turned on.

MP5403

SW2

FB1

FB2

SW1

R1

R2

R3

R4

Figure 5: Feedback Resistor Dividers to Set the

Output Voltages

The divider current is recommended to be

higher than 500nA to avoid influence from the

feedback node leakage current (which is in the

10nA level). Additionally, considering control

loop

optimization,

the

pull-up

resistor

is

recommended to be between

100kΩ to 500kΩ.

Then, the pull-down resistor can be calculated

with Equation (2):

1

V

6

.

0

V

)

3

orR

(

1

R

)

4

orR

(

2

R

OUT





(2)

Table 2 shows some typical output voltages

and their corresponding recommended resistor

divider values.

Table 2: Output Voltage vs. Resistor Values

R1

R2

1.2V

300k

Ω

300k

Ω

1.5V

300k

Ω

200k

Ω

1.8V

300k

Ω

150k

Ω

2.5V

300k

Ω

95.3k

Ω

3.3V

300k

Ω

66.5k

Ω

Inductor Selection

The inductor has a great impact on several key

performances for the step-down switcher, such as

inductor

current

ripple,

output

voltage

ripple,

efficiency, and load transient response.

Calculate the inductor current ripple with Equation

(3):

SW

IN

OUT

IN

OUT

L

f

L

V

)

V

V

(

V

I











(3)

Calculate the inductor peak current with Equation

(4):

2

L

Load

Lpk

I

I

I







(4)

Choosing the inductance is a trade-off between the

output ripple, efficiency, and transient response. The

larger the inductance is, the smaller the output

ripple, but the slower the response. Choose an

inductance to make the ripple current 30% to 40% of

the max load current.

The inductor saturation current must be higher than

the inductor peak current.

The inductor also impacts the solution efficiency in

terms of conduction loss and coil-related loss.

Generally,

the

DC

resistance

provides

DC

conduction loss information. For AC conduction loss

and coil-related loss, please refer to the vendor

datasheet for more detailed information.

Input Capacitor Selection

The input capacitor reduces the surge current

drawn from the input and the switching noise

from the device. Select an input capacitor with a

switching frequency impedance less than the

input

source

impedance

to

prevent

high-

frequency switching current from passing to the

input source. Use low ESR ceramic capacitors

with

X5R

or

X7R

dielectrics

and

small

temperature coefficients. For most applications,

a

22μF capacitor is sufficient.