MP2149 –6V, 1A, LOW QUIESCENT CURRENT, DUAL, SYNC BUCK REGULATOR

MP2149 Rev.1.01

www.MonolithicPower.com

9

5/31/2013

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© 2013 MPS. All Rights Reserved.

OPERATION

MP2149 is a fully-integrated, dual-channel,

synchronous,

step-down

converter.

Both

channels have peak-current modes with internal

compensation for faster transient responses

and cycle-by-cycle current limits.

MP2149 is optimized for low-voltage, portable

applications where efficiency and small size are

critical.

180° Phase-Shift

By default, the MP2149’s two channels operate

at a 180° phase-shift to reduce input current

ripple: The smaller current ripple allows for a

smaller input bypass capacitor. In CCM, two

internal clocks control the switching: The high-

side MOSFET turns on at the corresponding

CLK’s rising edge.

CLK1

CLK2

SW1

SW2

t

Figure 2: Clock/Switching Timing

However, the switching frequency for each

channel falls when operating at low dropout, so

the MP2149 operates at a default switching

frequency of 1MHz with a fixed OFF time. After

the input voltage recovers, switching for PWM

mode resumes normally and synchronizes with

the master oscillator for phase-shifted operation.

Light-Load Operation

In light loads, the MP2149 uses a proprietary

control scheme to save power and improve

efficiency. The MP2149 will turn off the low side

switch when inductor current starts to reverse.

Then

MP2149

works

in

discontinuous

conduction mode (DCM) operation.

When either channel enters DCM or low-

dropout operation, this channel will not be

controlled by the internal 1MHz oscillator.

Condition

Mode

CH1

CH2

CH1

CH2

1

Heavy Load

1MHz

CCM

1MHz

CCM,0°

Phase

2

Light Load

DCM

DCM

3

Low Dropout

Fixed OFF

Time

Fixed OFF

Time

4

Heavy

Load

Light

Load

0.95MHz

CCM

DCM

5

Light

Load

Heavy

Load

DCM

0.95MHz

CCM

6

Heavy

Load

Low

Dropout

0.95MHz

CCM

Fixed OFF

Time

7

Low

Dropout

Heavy

Load

Fixed OFF

Time

0.95MHz

CCM

8

Light

Load

Low

Dropout

DCM

Fixed OFF

Time

9

Low

Dropout

Light

Load

Fixed OFF

Time

DCM

Soft Start

MP2149 has a built-in soft start that ramps up

the output voltage at a controlled slew rate to

start-up overshoot. The soft-start time is ~0.5ms.

Current Limit and Short-Circuit Recovery

Each channel’s high-side switch has a 2.5A

(typ.) current limit. The MP2149 treats any

current-limit condition that remains for 400us as

a short and enter hiccup mode.

The MP2149 disables its output power stage in

hiccup mode, and then slowly discharges the

soft-start capacitor before initiating soft-start. If

the short-circuit condition remains, the MP2149

repeats this operation till the short circuit

disappears and output returns to the regulation

level.