MP2276

– 16V, 8A, HIGH EFFICIENCY, SYNC, STEP-DOWN CONVERTER

MP2276 Rev.1.0

www.MonolithicPower.com

14

3/22/2017

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© 2017 MPS. All Rights Reserved.

OPERATION

Constant-On-Time (COT) Control

The MP2276 employs constant-on-time (COT)

control to achieve a fast load transient response.

Figure 2 shows details of the control stage of

the MP2276.

The operational amplifier (AMP) corrects any

MP2276 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 MP2276 has internal RAMP compensation

to support low ESR MLCC output capacitor

solutions.

The adaptive

internal RAMP

is

optimized so that the MP2276 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

VREF

FB

PWM

Comparator

AGND

AMP

Vsens+

Vsens-

Σ

+

L

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) turns 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 MP2276 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 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

HS-FET

Driver

LS-FET

Driver

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 MP2276 can also be configured to

operate in forced CCM operation when the

output current is low. See the FREQ/MODE

Selection section on page 15 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

At light-load condition, the MP2276 can be

configured to work in pulse-skip mode to

optimize efficiency. When the load decreases,

the inductor current decreases as well. Once

the inductor current reaches zero, the MP2276

transitions from CCM to pulse-skip mode if the

MP2276

is

configured

so.

See

the

FREQ/MODE Selection section on page 15 for

details.