MP2116 –2A, 6V, 100% DUTY CYCLE SYNCHROOUS STEP-DOWN CONVERTER WITH 0.5A LDO

MP2116 Rev.1.0

www.MonolithicPower.com

11

1/17/2013

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© 2013 MPS. All Rights Reserved.

APPLICATION INFORMATION

Output Voltage Setting

The external resistor divider sets the output

voltage. The feedback resistor R1 of the switcher

also sets the feedback loop bandwidth with the

internal compensation capacitor (see Figure1).

Choose R1 feedback resistor of the switcher

between 450kΩ and 800kΩ for optimal transient

response. R2 is then given by:

OUT1

R1

R2

V

1

0.6V

=

−

See Table1 for recommended R1 & R2 resistor

values.

Choose R4 of the LDO between 10kΩ and

100kΩ. R3 is then given by:

OUT2

V

R3 R4 (

1)

0.6V

=×

−

Table 1—Resistor Selection vs. Output

Voltage Setting

R1

R2

1.2V

499k

499k

1.5V

499k

332k

1.8V

499k

249k

2.5V

499k

158k

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

<100mΩ.

See

Table

2

for

recommended inductors and manufacturers.

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

×

Δ

×

−

×

=

inductor ripple current approximately 30% of the

maximum load current, up to 2A.

The maximum inductor peak current is:

L

L(MAX)

LOAD(MAX)

I

II

2

Δ

=+

The input capacitor reduces the surge current

drawn from the input and switching noise from

the device. The input capacitor impedance at

the switching frequency shall be less than input

source impedance to prevent high frequency

switching current passing to the input. Ceramic

capacitors with X5R or X7R dielectrics are

highly recommended because of their low ESR

and small temperature coefficients. For most

applications,

a

10μF~22μF

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 most applications, a 22μF~47μF capacitor

is sufficient.

(

)

OUT1

IN1

OUT1

OUT1

IN1

OSC

OSC

O1

VV

V

1

V

ESR

Vf

L

8 f

C

×−

⎛⎞

Δ≤

×

+

⎜⎟

××

××

⎝⎠

Table 2—Suggested Surface Mount Inductors

Manufacturer

Part Number

Inductance (uH)

Max DCR

(mΩ)

Saturation

Current (A)

Dimensions

L x W x H (mm3)

TOKO

D62LCB

1.0

17

3.5

6.2 X6.3 X 2.0

SUMIDA

CDRH4D28C

1.0

17.5

3.0

5.1 X 5.1 X 3

DELTA

SIL525-1R0

1.0

38

3.2

5.0 X 5.0 X 2.5