MPQ8626 – 16V, 6A, HIGH EFFICIENCY SYNC, STEP-DOWN CONVERTER W/ ADJUSTABLE CURRENT LIMIT

MPQ8626 Rev. 1.1

www.MonolithicPower.com

13

8/16/2022

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

© 2022 MPS. All Rights Reserved.

OPERATION

Constant-On-Time (COT) Control

The MPQ8626 employs constant-on-time (COT)

control to achieve fast load transient response.

Figure 2 shows the details of the control stage

of the MPQ8626.

The operational amplifier (AMP) corrects any

error voltage between FB and REF. The

MPQ8626 can use AMP to provide excellent

load regulation over the entire load range,

whether it is operating in forced continuous

conduction mode (CCM) or pulse-skip mode.

The MPQ8626 has internal ramp compensation

to support low ESR MLCC output capacitor

solutions.

The

adaptive

internal

ramp

is

optimized so that the MPQ8626 is stable in the

entire operating input/output voltage range with

a proper design of the output L/C filter.

Adaptive

RAMP

ON

Timer

PWM

COMP +

VREF

FB

PWM

Comparator

AGND

AMP

Vsens+

Vsens-

Σ

+

L

COUT

VIN

PGND

SW

HSFET

LSFET

Figure 2: COT Control

Pulse-Width Modulation (PWM) Operation

Figure 3 shows how the pulse-width modulation

(PWM) signal is generated. AMP corrects any

error between FB and REF and generates a

fairly smooth DC voltage (COMP). The internal

ramp

is

superimposed

onto

COMP.

The

superimposed COMP is compared with the FB

signal.

Whenever

FB

drops

below

the

superimposed COMP, the integrated high-side

MOSFET (HS-FET) is turned on and remains

on for a fixed turn-on time. The fixed on time is

determined by the input voltage, output voltage,

and selected switching frequency. After the on

period elapses, the HS-FET turns off. The HS-

FET turns on again when FB drops below the

superimposed

COMP.

By

repeating

this

operation, the MPQ8626 regulates the output

voltage. The integrated low-side MOSFET (LS-

FET) turns on when the HS-FET is in its off

state to minimize conduction loss.

A dead short occurs between VIN and PGND if

both the HS-FET and the LS-FET are turned on

at the same time. This is called a shoot-

through. To avoid shoot-through, a dead time

(DT) is generated internally between the HS-

FET off and the LS-FET on period or the LS-

FET off and the HS-FET on period.

PWM

REF

RAMP

FB

COMP

TON

HS-FET

Driver

LS-FET

Driver

IL

IO

Figure 3: Heavy-Load Operation (PWM)

Continuous

Conduction

Mode

(CCM)

Operation

Continuous conduction mode (CCM) occurs

when the output current is high and the inductor

current is always above zero amps (see Figure

3). The MPQ8626 can also be configured to

operate in forced CCM operation when the

output current is low. See the MODE Selection

section on page 14 for details.

In CCM operation, the switching frequency is

fairly constant (PWM mode), so the output

ripple remains almost constant throughout the

entire load range.

Pulse-Skip Operation (PSM)

At light-load condition, the MPQ8626 can be

configured to work in pulse-skip mode (PSM) to

optimize efficiency. When the load decreases,

the inductor current decreases as well. Once

the

inductor

current

reaches

zero,

the

MPQ8626 transitions from CCM to PSM if the

MPQ8626 is configured in this way. See the

MODE Selection section on page 14 for details.