MP2166

– 6V, DUAL 2A/2A OR 3A/1A, SYNC, BUCK REGULATOR WITH PG AND SS

MP2166 Rev. 1.0

www.MonolithicPower.com

16

3/14/2017

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

© 2017 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Output Voltage

The external resistor divider sets the output

voltage. The feedback resistor (R1) also sets

the feedback loop bandwidth with the internal

compensation (see Figure 5).

FB

VOUT

R1

R2

Figure 5: External Resistor Divider

In the case of ceramic capacitors used as

switching

frequency

for

optimal

transient

performance and good phase margin. If an

electrolytic

capacitor

is

used,

the

loop

bandwidth is no higher than 1/4 of the ESR zero

Equation (2):

ESR

ESR

O

1

f

2

R

C



 



(2)

R1 is estimated to be 10

0kΩ. R2 can then be

calculated with Equation (3):

OUT

R1

R2

V

1

0.6V





(3)

Use Table 1 to select resistor values based on

different output voltages.

Table 1: Resistor Selection vs. Output Voltage

Setting

R1

R2

1.2V

100k

Ω

100k

Ω

1.5V

100k

Ω

66.5k

Ω

1.8V

100k

Ω

49.9k

Ω

2.5V

100k

Ω

31.6k

Ω

3.3V

100k

Ω

22.1k

Ω

Inductor Selection

An inductor with a DC current rating at least

25% higher than the maximum load current is

recommended for most applications. For best

efficiency, the inductor DC resistance should be

less

than

20mΩ. For most designs, the

inductance value can be derived from Equation

(4):

SW

L

IN

OUT

IN

OUT

f

I

V

)

V

-

(V

V

L











(4)

Where

inductor ripple current to be approximately 30%

of the maximum load current.

The maximum inductor peak current can be

calculated with Equation (5):

L

L(MAX)

LOAD

ΔI

I

= I

+

2

(5)

Input Capacitor Selection

The input capacitor reduces the surge current

drawn from the input and the switching noise

from the device. The input capacitor impedance

at the switching frequency should be less than

the input source impedance to prevent high-

frequency switching current from passing to the

input source. Ceramic capacitors with X5R or

X7R

dielectrics

are

highly

recommended

because

of

their

low

ESR

and

small

temperature coefficients. For most applications,

a 22µF capacitor is sufficient.

Output Capacitor Selection

voltage ripple small and ensures a stable

regulation

loop.

The

output

capacitor

impedance should be low at the switching

frequency. Use ceramic capacitors with X5R or

X7R dielectrics. If an electrolytic capacitor is

used, pay close attention to the output ripple

voltage, extra heating, and the selection of the

upper feedback resistor due to the large ESR of

electrolytic capacitor (refer to the Setting the

Output Voltage section). The output ripple

(

∆V

)

8

1

(

Co

f

ESR

f

L

V

)

V

-

(V

V

V

SW

SW

IN

OUT

IN

OUT

OUT



















(6)