MP2113 – 1.5A, SYNCHRONOUS STEP-DOWN CONVERTER WITH DYNAMIC VOLTAGE CONTROL

MP2113 Rev. 1.0

www.MonolithicPower.com

8

4/4/2011

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© 2011 MPS. All Rights Reserved.

OPERATION

Main

Switch

(PCH)

Synchronous

Rectifier

(NCH)

+

-

COMP

DL

DH

0.04

Reverse-

Current Stop

Comparator

PWM

Control

Logic

IAMP

10X

+

-

Current

Sense Amp

EAMP

+

-

Feedback

Error Amp

PWM

Slope Comp

+

+

-

PWMCMP

ICS

1.5MHz

Oscillator

OSC

FB

Bias

&

Voltage

Reference

0.6V

EN

FB

SW

EAO

CC

17pF

RZ

1.2Meg

CTRL

DRN

PGOOD

+

-

PG_COMP

0.66V

0.66V

Schottky

Diode

DC

Vth

NOFF

Async.

Control

(fixed-on

PFM)

0.60V

0.54V

-

+

0.54V

IN

GND

Figure 1-Functional Block Diagram

The MP2113 is a fixed frequency 1.5MHz

current mode 1.5A step-down converter with

dynamic voltage control. It has user selectable

two operation modes: forced PWM mode for

high load and asynchronous mode for light

load. The output voltage for each mode can be

set independently, through an external resistor

divider and a control pin.

MP2113 is optimized for low voltage, Li-Ion

battery

powered

applications

where

high

efficiency and small size are critical.

Forced PWM Mode

The forced PWM mode uses a high side PFET

main switch and a low side synchronous

rectifier, and always operates in continuous

conduction mode. Thus it simplifies the control

scheme and eliminates the random spectrum

noise due to discontinuous conduction mode.

The steady state duty cycle D for this mode can

be calculated as:

%

100

V

V

%

100

f

T

D

IN

OUT

OSC

ON

×

≈

×

×

=

is the oscillator frequency (1.5MHz typ.).

Current Mode PWM Control

Slope compensated current mode PWM control

provides stable switching and cycle-by-cycle

current limiting for superior load and line

response as well as protection of the internal

main switch and synchronous rectifier. The

MP2113 switches at a constant frequency

(1.5MHz) and modulates the inductor peak

current

to

regulate

the

output

voltage.

Specifically, for each cycle the PWM controller

forces the inductor peak current to an internal

reference level derived from the feedback error

voltage. At normal operation, the main switch is

turned on at each rise edge of the internal

oscillator, and remains on for a certain period of

time to ramp up the inductor current. As soon

as the inductor current reaches the reference

level, the main switch is turned off and

immediately the synchronous rectifier will be

turned on to provide the inductor current. In

forced PWM mode, the synchronous rectifier

will stay on until the next oscillator cycle.