MP9162A – 2A, 6V, 1.5MHz, SYNCHRONOUS, STEP-DOWN CONVERTER

MP9162A Rev. 1.01

www.MonolihicPower.com

11

7/5/2016

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© 2016 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Output Voltage

The external resistor divider sets the output

voltage (see the Typical Application on page 1).

The feedback resistor (R1) cannot be too large

or too small, considering the trade-off between

a dynamic circuit and stability in the circuit. Set

R1 to be around 120kΩ to 200kΩ. R2 can then

be calculated with Equation (2):

out

R1

R2

V

1

0.6





(2)

The feedback circuit is shown in Figure 2.

R1

R2

Vout

FB

MP9162A

Figure 2: Feedback Network

Table 1 lists the recommended resistor values

for common output voltages.

Table 1: Resistor Selection for Common Output

Voltages

R1 (kΩ)

R2 (kΩ)

1.0

200 (1%)

300 (1%)

1.2

200 (1%)

200 (1%)

1.8

200 (1%)

100 (1%)

2.5

200 (1%)

63.2 (1%)

3.3

200 (1%)

44.2 (1%)

Selecting the Inductor

A 0.68µH-to-2.2µH inductor is recommended

for most applications. For the highest efficiency,

choose an inductor with a DC resistance of less

than 15mΩ. For most designs, the inductance

value can be derived from Equation (3):

OUT

IN

OUT

1

IN

L

OSC

V(V

V

)

L

VI

f





 

(3)

Set the inductor current to be approximately

30% of the maximum load current. The

maximum inductor peak current is calculated in

Equation (4):

2

I

I

I

L

LOAD

)

MAX

(

L







(4)

Selecting the Input Capacitor

The input current to the step-down converter is

discontinuous and requires a capacitor to

supply the AC current to the step-down

converter while maintaining the DC input

voltage. For best performance, use low ESR

capacitors. Ceramic capacitors with X5R or

X7R dielectrics are highly recommended

because of their low ESR values and small

temperature coefficients. For most applications,

a 10µF capacitor is sufficient. For a higher

output voltage, a 47µF capacitor may be

needed to improve system stability.

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 with Equation (5):

























IN

OUT

IN

OUT

LOAD

1

C

V

V

1

V

V

I

I

(5)

shown in Equation (6):

2

I

I

LOAD

1

(6)

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, use a small, high-quality ceramic

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

as possible. When using ceramic capacitors,

ensure that they have enough capacitance to

provide a sufficient charge to prevent excessive

voltage ripple at the input. The input voltage

ripple caused by capacitance can be estimated

with Equation (7):

LOAD

OUT

OUT

IN

IN

SIN

IV

V

V1

fC1

V

V







 







(7)