MP1660

– SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS

MP86953 Rev. 1.0

www.MonolithicPower.com

12

6/9/2020

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© 2020 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Output Voltage

The external resistor divider is used to set the

output voltage. First, carefully choose a value

for R2. A small R2 leads to considerable

quiescent current loss, while a large R2 makes

FB noise-sensitive. R2 should be between 5

kΩ

and

100kΩ. Typically, it is recommended to set

the R2 current to be between 5

μA and 30μA for

a good balance between system stability and

no-load

loss.

R1

can

be

calculated

with

Equation (2):

OUT

REF

REF

VV

R1

R2

V





(2)

Figure 4 shows the feedback circuit.

MP1660

FB

R1

R2

VOUT

RT

Figure 4: Feedback Network

Table 1 lists the recommended resistor values

for common output voltages.

Table 1: Parameters Selection for Common

Output Voltages (9)

VOUT (V)

R1

(kΩ)

R2

(kΩ)

RT (

kΩ)

L

(μH)

5

40.2

5.49

18

4.7

3.3

40.2

8.87

18

4.7

2.5

40.2

12.7

30

3.3

1.8

40.2

20

39

2.2

1.5

40.2

26.7

28

2.2

1.2

40.2

40.2

62

1.5

1

40.2

60.4

82

1.5

Note:

9)

For a detailed design circuit, see the Typical Application

Circuits section on page 15.

Selecting the Inductor

Optimized Performance with

MPS Inductor

An inductor is necessary to supply constant

current to the output load while being driven by

the switched input voltage. A larger-value

inductor results in less ripple current and lower

output ripple voltage, but also has a larger

physical footprint, higher series resistance, and

lower

saturation

current.

A

good

rule

to

determine the inductance value is to design the

peak-to-peak ripple current in the inductor to be

between 30% and 40% of the maximum output

current. The peak inductor current should be

below the maximum switch current limit. The

inductance

value

can

be

calculated

with

Equation (3):

OUT

OUT

SW

L

IN

VV

L

(1

)

f

I

V



 



(3)

Where

∆IL is the peak-to-peak inductor ripple

current.

The inductor should not saturate under the

maximum inductor peak current. The peak

inductor

current

can

be

calculated

with

Equation (4):

OUT

OUT

LP

OUT

SW

IN

VV

I

I

(1

)

2f

L

V





 



(4)

MPS inductors are optimized and tested for use

with our complete line of integrated circuits.

Table

2

lists

our

power

inductor

recommendations. Select a part number based

on your design requirements.

Table 2: Power Inductor Selection

Part Number

Inductor

Value

Manufacturer

MPL-AL6050-4R7

4.7

μH

MPS

MPL-AL6050-3R3

3.3

μH

MPS

MPL-AL6050-2R2

2.2

μH

MPS

MPL-AL6050-1R5

1.5

μH

MPS

Visit MonolithicPower.com under Products >

Inductors for more information.

Selecting the Input Capacitor

The step-down converter has discontinuous

input current, and requires a capacitor to supply

AC current to the step-down converter while

maintaining the DC input voltage. Ceramic

capacitors are recommended for the best

performance, and should be placed as close to

VIN as possible. Capacitors with X5R and X7R

ceramic dielectrics are recommended because

they

are

fairly

stable

amid

temperature

fluctuations.