MP28162 – SINGLE-INDUCTOR, BUCK-BOOST CONVERTER WITH 1.5A MOSFETS

MP28162 Rev. 1.0

MonolithicPower.com

16

3/16/2023

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© 2023 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Output Voltage

The external resistor divider sets VOUT. Select

the R2 value first. A small R2 value leads to

considerable quiescent current (IQ) loss while a

too large R2 value makes the FB sensitive to

noise. It is recommended to choose a value

between

10kΩ and 100kΩ for R2. R1 can then

be calculated with Equation (1):

2

R

)

1

V

V

(

1

R

FB

OUT



−

=

(1)

Selecting the Inductor

Optimized Performance with MPS Inductor

MPL-AT2010 Series

With

one

buck-boost

topology

circuit,

the

inductor must support the buck application with

the

maximum

VIN

(VIN_MAX)

and

boost

application with the minimum VIN (VIN_MAX). The

minimum buck inductance (LMIN_BUCK) can be

determined based on the buck mode current

ripple, which is calculated with Equation (2):

OUT

IN _ MAX

OUT

MIN _ BUCK

IN _ MAX

REQ

L

V

(V

V

)

L

V

f

I

−

=



 

(2)

Where fREQ is the switching frequency, and ∆IL

is the peak-to-peak IL ripple.

The minimum boost inductance (LMIN_BOOST) can

be determined based on the boost mode

current ripple, which is calculated with Equation

(3):

IN _ MIN

OUT

IN _ MIN

MIN _ BOOST

OUT

REQ

L

V

(V

V

)

L

V

f

I

−

=



 

(3)

The minimum inductance for the application

must exceed the calculated LMIN_BUCK and

LMIN_BOOST from Equation (2) and Equation (3),

respectively.

The inductor must also support the peak buck

current (IPEAK_BUCK) and peak boost current

(IPEAK_BOOST) to avoid saturation:

IPEAK_BUCK can be calculated Equation (4):

OUT

IN _ MAX

OUT

PEAK _ BUCK

OUT

IN _ MAX

REQ

V

(V

V

)

II

2 V

f

L

−

=+







(4)

IPEAK_BOOST can be calculated with Equation (5):

IN _ MIN

OUT

IN _ MIN

OUT

OUT

PEAK _ BOOST

IN _ MIN

OUT

REQ

V

(V

V

)

VI

I

V

2 V

f

L

−



=+









(5)

Where η is the estimated efficiency.

MPS inductors are optimized and tested for use

with a complete line of integrated circuits. Table

1 lists the power inductor recommendations.

Select a part number based on the design

requirements.

Table 1: Power Inductor Selection

Part Number

Inductance

Manufacturer

MPL-AT2010-1R0

1

μH

MPS

MPL-AT2010-1R5

1.5

μH

MPL-AT2010-2R2

2.2

μH

Visit MonolithicPower.com under Products >

Inductors for more information.

Selecting the Input and Output Capacitors

It is recommended to select ceramic capacitors

with a low ESR for the input capacitor (CIN) and

output

capacitor

(COUT).

This

filters

any

disturbances in the input and output line and

achieves stable operation.

COUT affects loop stability. CIN and COUT must be

placed as close as possible to the device. See

Figure 4 on page 18 for more details on

optimizing the capacitor selection.

Design Example

Table 2 shows a design example following the

application guidelines for the specifications

below.

Table 2: Design Example

Start-Up VIN

(V)

Operating VIN

(V)

VOUT (V)

1.8 to 5.5

1.2 to 5.5

3.3

Figure 4 on page 18 shows the detailed

application circuit. The typical performance and

waveforms

are

shown

in

the

Typical

Performance Characteristics section on page 7.