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

MP2113 Rev. 1.0

www.MonolithicPower.com

10

4/4/2011

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2011 MPS. All Rights Reserved.

APPLICATION INFORMATION

Output Voltage Setting

The external resistor divider sets the output

voltage. The resistor R1 also sets the feedback

loop bandwidth for the step-down converter. (see

Figure 1).

Choose R1 to be between 200k-300kΩ for

optimal transient response. R2 is calculated

using

the

desired

output

voltage

for

asynchronous mode:

1

6

.

0

1

2

_

−

=

V

V

R

R

ASYNC

OUT

R3 is then calculated using R1, R2 and the

desired output voltage for forced PWM mode:

1

2

1

2

6

.

0

2

1

3

_

−

+

⋅

=

R

R

R

V

V

R

R

R

FPWM

OUT

If one want to have the same output voltage

level for both operation mode, R3 will not be

needed.

Table 1—Resistor Selection vs. Output

Voltage Setting

R1

R2

R3

0.9V/1.8V

301kΩ

(1%)

604kΩ

(1%)

200kΩ

(1%)

1.2V/1.8V

301kΩ

(1%)

301kΩ

(1%)

301kΩ

(1%)

1.2V/2.5V

301kΩ

(1%)

301kΩ

(1%)

137kΩ

(1%)

1.5V/3.3V

301kΩ

(1%)

200kΩ

(1%)

100kΩ

(1%)

Inductor Selection

A 1µH to 10µH inductor with DC current rating

at least 25% higher than the maximum load

current is recommended for most applications.

For best efficiency, the inductor DC resistance

shall be <200mΩ. For most designs, the

inductance value can be derived from the

following equation:

()

OSC

L

IN

OUT

IN

OUT

f

I

V

V

V

V

L

×

∆

×

−

×

=

inductor ripple current approximately 30% of the

maximum load current, 1.5A.

The maximum inductor peak current is:

2

I

I

I

L

LOAD

)

MAX

(

L

∆

+

=

Table 2—Suggested Inductors

Manufacturer

Part

Number

Inductance

(µH)

Dimensions

LxWxH

(mm

Wruth

7447745022

2.2

5.8X5.2X2

Toko

636CY-

2R2M

2.2

6.8X6X3.5

TDK

VLCF5020T-

2R2N2R6-1

2.2

5X5X2

The input capacitor reduces the surge current

drawn from the input and switching noise from

the device. Ceramic capacitors with X5R or

X7R dielectrics are highly recommended

because

of

their

low

ESR

and

small

temperature coefficients. For most applications,

a 4.7µF capacitor is sufficient.

The output capacitor keeps output voltage

ripple small and ensures regulation loop stable.

The output capacitor impedance shall be low at

the switching frequency. Ceramic capacitors

with X5R or X7R dielectrics are recommended.

For forced PWM mode operation, the output

)

1

8

1

(

)

(

OUT

OSC

ESR

OSC

IN

OUT

IN

OUT

OUT

C

f

R

L

f

V

V

V

V

V

⋅

⋅

+

⋅

⋅

−

⋅

=

∆

For asynchronous mode operation, the output

ripple is the scaled amplitude of the feedback

threshold hysteresis window:

()

2

2

1

594

.

0

606

.

0

R

R

R

V

V

V

OUT

+

⋅

−

=

∆

Thermal Dissipation

Power dissipation shall be considered when

MP2113 operates at maximum 1.5A output

current. If the junction temperature rises above

150

°C, MP2113 will be shut down by internal

thermal protection circuitry.

The junction-to-ambient thermal resistance of

The maximum allowable power dissipation is