MP2176 – 6V, 6A, SYNCHRONOUS, STEP-DOWN CONVERTER

MP2176 Rev. 1.0

www.MonolithicPower.com

19

4/17/2018

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© 2018 MPS. All Rights Reserved.

For simplification, the output ripple can be

approximated with Equation (24):

OUT

OUT

OUT

ESR

SW

IN

VV

V

(1

) R

f

L

V





 





(24)

Selecting the Inductor

An inductor is required to supply constant

current to the output load while being driven by

the switching input voltage. A larger-value

inductor results in less ripple current and lower

output ripple voltage but also has a larger

physical size, higher series resistance, and

lower saturation current. A good rule for

determining the inductor value is to allow the

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

approximately 10 ~ 30% of the maximum output

current. Also, ensure that the peak inductor

current is below the current limit of the device.

The inductance value can be calculated with

Equation (25):

OUT

OUT

SW

L

IN

VV

L

(1

)

f

I

V



 



(25)

Where

∆IL is 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

with

Equation (26):

OUT

OUT

LP

OUT

SW

IN

VV

I

I

(1

)

2 f

L

V





 



(26)

The inductors listed in Table 1 are highly

recommended for the high efficiency they can

provide.

Typical Design Parameter Tables

The tables on page 20 include recommended

component values for typical output voltages

(1.0V,

1.2V,

1.8V,

3.3V)

and

switching

frequencies (600kHz, 800kHz, 1MHz). Refer to

Table 2 and Table 3 for design cases without

external ramp compensation. Refer to Table 4

and Table 5 for design cases with external

ramp compensation. An external ramp is not

required when high ESR capacitors, such as

electrolytic or POSCAPs, are used. An external

ramp is required when low ESR capacitors,

such as ceramic capacitors, are used. For

cases not listed in this datasheet, a calculator in

an Excel spreadsheet can also be requested

through an MPS sales representative to assist

with the calculation.