MP2326 Rev. 1.1

www.MonolithicPower.com

12

1/28/2016

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

© 2016 MPS. All Rights Reserved.

OPERATION

PWM Operation

The MP2326 is a fully integrated, synchronous,

rectified, step-down, switch converter. The device

uses constant-on-time (COT) control to provide

fast

transient

response

and

easy

loop

compensation. Fig. 2 shows the MP2326s

simplified ramp compensation block. At the

beginning of each cycle, the high-side MOSFET

is lower than the error amplifier output voltage

The input voltage and the frequency-set resistor

After the on period elapses, the HS-FET enters

the off state. By cycling the HS-FET between the

on and off states, the converter regulates the

output voltage. The integrated low-side MOSFET

(LS-FET) turns on during the HS-FETs off state

to minimize the conduction loss.

Shoot-through occurs when both the HS-FET

and the LS-FET are turned on at the same time,

causing a dead short between the input and GND.

Shoot-through reduces efficiency dramatically.

The MP2326 avoids shoot-through by internally

generating a dead-time (DT) between the HS-

FET off-time and the LS-FET on-time, and the

LS-FET off-time and the HS-FET on-time.

Depending on the output current, the device

enters either heavy-load operation or light-load

operation.

FIGURE 2. Simplified Ramp Compensation Block

MODE Selection

Connecting a resistor (R6) from FREQ/MODE to

VIN sets the switching frequency (see Fig. 3).

Meanwhile, the part works in forced PWM mode.

Connect a resistor (R7) from FREQ/MODE to

GND to set the switching frequency. Meanwhile,

the part works in auto PFM/PWM mode.

FIGURE 3.Mode Selection

Switching Frequency

MP2326 uses constant-on-time (COT) control;

there is no dedicated oscillator in the IC. The

input voltage is feed-forwarded to the on-time

one-shot timer through the frequency resistor.

switching frequency is fairly constant over the

input voltage range. The approximate typical

switching frequency can be determined with the

following equation:

6

SW

IN

on

OUT

10

F(kHz)

V(V)

T(ns)

V(V)





(1)

and auto PFM/PWM mode.

The approximate

Forced PWM mode:

FREQ

ON _ PWM

DELAY _ PWM

IN

14.5 R

(k )

TT

(ns)

V(V) 0.4









(2)

Auto PFM/PWM mode:

FREQ

ON _ PFM

DELAY _ PFM

IN

13 R

(k )

TT

(ns)

V(V) 0.4









(3)

comparator delay. The typical value equals

approximately 15ns and 10ns, respectively.

When the part enters CCM mode, the duty ratio

changes slightly from light load to full load due to

power loss. This causes the frequency to change

slightly from light load to full load even in CCM

mode.