MPM3606 – SYNCHRONOUS STEP-DOWN MODULE WITH INTEGRATED INDUCTOR

MPM3606 Rev. 1.0

www.MonolithicPower.com

13

8/11/2014

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

© 2014 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Output Voltage

The external resistor divider sets the output

voltage (see Typical Application on page 1).

The feedback resistor R1 also sets the

feedback loop bandwidth with the internal

compensation

capacitor

(see

Typical

Application on page 1). Choose R1 refer to

Table 1, R2 is then given by:

OUT

R1

R2

V

1

0.798V





Figure 5: Feedback Network

Table 1 lists the recommended resistors value

for common output voltages.

Table 1: Resistor Selection for Common Output

Voltages

R1 (kΩ)

R2 (kΩ)

(9)

1.0

221

887

9.09

1.2

191

383

11.3

1.5

158

180

13

1.8

102

82

18.2

2.5

75

34.8

25.5

3.3

75

24

33

5

100

19.1

45.3

Notes:

please refer to Figure 7 for full input and output voltage

Normally output voltage is recommended to be

set from 0.8V to 5.5V. Actually it can be set

larger than 5.5V. Output voltage ripple will be

larger in this case. Additional output capacitor

may be needed to reduce the output voltage

ripple.

When output voltage is high, the chip’s heat

dissipation become more important, please

refer to PC Board layout guidelines on page 14-

15 to achieve better thermal effect.

Selecting the Input Capacitor

The input current to the step-down converter is

discontinuous, therefore requires a capacitor is

to supply the AC current to the step-down

converter while maintaining the DC input

voltage. Use low ESR capacitors for the best

performance. Use ceramic capacitors with X5R

or X7R dielectrics for best results because of

their

low

ESR

and

small

temperature

coefficients. For most applications, use a 10µF

capacitor.

Since C1 absorbs the input switching current, it

requires an adequate ripple current rating. The

RMS current in the input capacitor can be

estimated by:

























IN

OUT

IN

OUT

LOAD

1

C

V

V

1

V

V

I

I

where:

2

I

I

LOAD

1

For simplification, choose an input capacitor

with an RMS current rating greater than half of

the maximum load current.

The input capacitor can be electrolytic, tantalum

or ceramic. When using electrolytic or tantalum

capacitors, add a small, high quality ceramic

capacitor (e.g. 0.1μF) placed as close to the IC

as possible. When using ceramic capacitors,

make sure that they have enough capacitance

to

provide

sufficient

charge

to

prevent

excessive voltage ripple at input. The input

voltage ripple caused by capacitance can be

estimated as:

LOAD

OUT

OUT

IN

IN

SIN

IV

V

V1

fC1

V

V







 







Setting the AAM Voltage

The AAM voltage is used to set the transition

point from AAM to CCM. It should be chosen to

provide the best combination of efficiency,

stability, ripple, and transient.

If the AAM voltage is set lower, then stability

and ripple improves, but efficiency during AAM

mode and transient degrades. Likewise, if the

AAM voltage is set higher, then the efficiency

during AAM and transient improves, but stability