MP2160 – 1.2A PEAK, 6V, 3.5MHz SYNCHRONOUS STEP-DOWN SWITCHER

MP2160 Rev. 1.03

www.MonolihicPower.com

10

7/5/2016

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APPLICATION INFORMATION

COMPONENT SELECTION

Setting the Output Voltage

The external resistor divider is used to set the

output voltage (see Typical Application on page

1). The feedback resistor R1 can not be too

large neither too small considering the trade-off

for stability and dynamic. Choose R1 to be

around 40kΩ to 80kΩ. R2 is then given by:

out

R1

R2

V

1

0.6





The feedback circuit is shown as Figure 2.

R1

R2

Vout

FB

MP2160

Figure 2: 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)

1.0

40(1%)

60(1%)

1.2

40(1%)

40(1%)

1.8

60(1%)

30(1%)

2.5

80(1%)

25(1%)

3.3

80(1%)

17.7(1%)

Selecting the Inductor

A 0.15µH to 1µH inductor is recommended for

most applications. For highest efficiency, the

inductor DC resistance should be less than

15mΩ. For most designs, the inductance value

can be derived from the following equation.

OUT

IN

OUT

1

IN

L

OSC

V(V

V

)

L

VI

f





 

Choose inductor current to be approximately

30% of the maximum load current. The

maximum inductor peak current is:

2

I

I

I

L

LOAD

)

MAX

(

L







Selecting the Input Capacitor

The input current to the step-down converter is

discontinuous, therefore a capacitor is required

to supply the AC current to the step-down

converter while maintaining the DC input

voltage. Use low ESR capacitors for the best

performance. Ceramic capacitors with X5R or

X7R dielectrics are highly recommended

because

of

their

low

ESR

and

small

temperature coefficients. For most applications,

a 10µF capacitor is sufficient. For higher output

voltage, 22μF may be needed for more stable

system.

Since the input capacitor 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 the input capacitor

whose 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, a small and high quality ceramic

capacitor, i.e. 0.1μF, should be 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 by:

LOAD

OUT

OUT

IN

IN

SIN

IV

V

V1

fC1

V

V







 





