MPQ4560

– 2A, 2MHz, 55V, STEP-DOWN CONVERTER

MPQ4560 Rev. 1.1

www.MonolithicPower.com

12

5/24/2016

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

© 2016 MPS. All Rights Reserved.

APPLICATION INFORMATION

COMPONENT SELECTION

Setting the Output Voltage

A resistive voltage divider from the output voltage

to FB pin sets the output voltage. The voltage

divider divides the output voltage down to the

feedback voltage by the ratio:

FB

OUT

R2

V =V

R1+R2



Thus the output voltage is:

OUT

FB

R1+R2

V

=V

R2



For example, the

value for R2 can be 10kΩ. With

this value, R1 is:

OUT

R1=12.5 (V

-0.8)(K

Ω)



So for a 3.3V output voltage, R2 is

10kΩ, and R1

is 31.6

kΩ.

Inductor

The inductor provides constant current to the

output load while being driven by the switched

input voltage. A larger-value inductor will result in

lower ripple current that will lower the output

ripple voltage. However, a larger inductor value

will be physically larger, have higher series

resistance, or lower saturation current.

To determine the inductance, allow the

inductor’s

peak-to-peak ripple current to approximately

equal 30% of the maximum switch current limit.

Make sure that the peak inductor current is less

than the maximum switch current limit. The

inductance value can be calculated by:

OUT

OUT

s

L

IN

VV

L1=

(1-

)

f

ΔI

V





the peak-to-peak inductor ripple current.

Choose an inductor that will not saturate under

the maximum inductor peak current. The peak

inductor current can be calculated by:

























IN

OUT

S

OUT

LOAD

LP

V

V

1

1

L

f

2

V

I

I

Table 1 lists several suitable inductors from

various manufacturers. The different inductor

choices include price vs. size requirements and

any EMI requirements.