MP2276

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

MP2276 Rev.1.0

www.MonolithicPower.com

15

3/22/2017

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

© 2017 MPS. All Rights Reserved.

Figure 4 shows pulse-skip mode operation at

light-load condition. When FB drops below the

superimposed COMP, the HS-FET turns on for

a fixed interval. When the HS-FET turns off, the

LS-FET turns on until the inductor current

reaches zero. In pulse-skip mode operation, FB

does not reach the superimposed COMP when

the inductor current approaches zero. The LS-

FET driver turns into tri-state (Hi-Z) when the

inductor current reaches zero. Therefore, the

output capacitors discharge slowly to PGND

through the FB resistors (R1 and R2). At light-

load condition, the HS-FET is not turned on as

frequently in pulse-skip mode as it is in forced

CCM. As a result, the efficiency in pulse-skip

mode is improved greatly compared to that in

forced CCM operation.

PWM

REF

RAMP

FB

COMP

HS-FET

Driver

LS-FET

Driver

Figure 4: Pulse Skip in Light Load

As the output current increases from the light-

load condition, the time period the current

modulator regulates in becomes shorter. The

HS-FET is turned on more frequently, and the

switching frequency increases accordingly. The

output current reaches the critical level when

the current modulator time is zero. The critical

level of the output current is determined with

Equation (1):

IN

SW

OUT

OUT

IN

OUT

V

F

L

2

V

)

V

V

(

I













(1)

The MP2276 enters PWM mode once the

output

current

exceeds

the

critical

level.

Afterward, the switching frequency remains

fairly constant over the output current range.

The MP2276 can be configured to operate in

forced CCM even in light-load condition (see

Table 1).

FREQ/MODE Selection

The

MP2276

provides

both

forced

CCM

operation and pulse-skip operation in light-load

condition. The MP2276 has three options for

switching

frequency

selection:

600kHz,

1100kHz, and 2000kHz. Select the operation

mode

under

light-load

condition

and

the

switching frequency by choosing the resistance

value of the resistor connected between MODE

and AGND or VCC (see Table 1).

Table 1: FREQ/MODE Selection

MODE

Light-Load

Mode

Switching

Frequency

AGND

Forced CCM

1100kHz

30.1kΩ (±20%)

to AGND

Forced CCM

2000kHz

60.4kΩ (±20%)

to AGND

Forced CCM

600kHz

121kΩ (±20%)

to AGND

Pulse Skip

600kHz

243kΩ (±20%)

to AGND

Pulse Skip

2000kHz

VCC

Pulse Skip

1100kHz

Soft Start (SS)

The minimum soft-start time is limited to 1.7ms.

This

can

be

increased

by

choosing

the

capacitor between SS/TRK and AGND. A

minimum value of 3.3nF for this capacitor is

always required to stabilize the reference

voltage.

The capacitance of this capacitor can be

determined with Equation (2) and Equation (3):

22

3

.

3

)

(





nF

C

SS

V

A

x

ms

t

nF

C

ss

SS

8

.

0

10

)

(

)

(



