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

MP28162 Rev. 1.0

MonolithicPower.com

13

3/16/2023

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

© 2023 MPS. All Rights Reserved.

OPERATION

The MP28162 is a high-efficiency, dual-mode,

buck-boost converter that provides an output

voltage (VOUT) exceeding, below, equal to the

input voltage (VIN). VOUT is sensed via the FB

pin

through

an

external

resistor

divider

connected from the output to ground (see

Figure 1 on page 12). The difference between

the FB pin voltage (VFB) and the internal

reference voltage (VREF) is amplified by the

error amplifier (EA) to generate a control signal

(VC_BUCK).

By

comparing

VC_BUCK

with

the

internal current ramp signal (the sensed SWA

current with slope compensation) via the buck

comparator, a pulse-width modulation (PWM)

control signal for the buck legs (SWA and SWB)

is generated.

Another control signal (VC_BOOST) is derived from

VC_BUCK through the level shift. VC_BOOST is

compared with the sensed SWA current with

slope compensation via the boost comparator

and generates a PWM control signal for the

boost legs (SWC and SWD). Figure 2 shows

the buck-boost converter

’s switching topology.

SWA

SWB

SWC

SW1

SW2

SWD

VIN

VOUT

Figure 2: Buck-Boost Switching Topology

Buck Region (VIN > VOUT)

If VIN significantly exceeds VOUT, the MP28162

can deliver energy to the load within

SWA’s

maximum duty cycle by switching SWA and

SWB. The converter operates in buck mode. In

this mode, SWD remains on and SWC is off.

VC_BUCK is typically compared with the current

ramp signal

to generate

a PWM output.

Therefore, SWA and SWB are pulse-width

modulated to produce the required duty cycle

and eventually support VOUT.

Buck-Boost Region (VIN ≈ VOUT)

If VIN is close to VOUT, the MP28162 is unable to

provide sufficient energy to the load due to

SWA’s maximum duty cycle. As a result, the

current ramp signal cannot trigger VC_BUCK

during the first period, and SWA remains on

with 100% duty cycle. If SWB does not turn on

during the first period, the converter enters

boost mode in the secondary period (where

SWC switches) and an offset voltage is added

to the current ramp signal to enable it to reach

VC_BUCK. SWC turns off when the current ramp

signal

intersects

with

VC_BOOST during

the

secondary period, and SWD conducts the

inductor current (IL) when SWC is off. This is

called boost operation.

SWA turns off when the current ramp signal

intersects with VC_BUCK in the secondary period,

and SWB turns on to conduct IL after SWA turns

off. This is called buck operation.

If SWB turns on during the secondary period,

boost operation (SWC on) is disabled in the

following cycle. If SWA continues to conduct

with 100% duty in the secondary cycle, the

boost operation is also enabled in the following

duty cycle. SWA and SWB, and SWC and SWD

switch during this condition simultaneously.

This is called buck-boost mode.

Boost Region (VIN < VOUT)

If VIN is significantly below VOUT, VC_BUCK

remains above the current ramp signal. The

offset voltage is added to the current signal,

which prevents SWB from turning on in all

cycles. The boost operation (SWC on) is

enabled in every cycle based on the logic,

resulting in only SWC and SWD switching. This

is called boost mode. In this mode, SWC and

SWD are pulse-width modulated to produce the

required duty cycle and eventually support VOUT

regulation.