MP2192

– 2A, SYNCHRONOUS STEP-DOWN CONVERTER WITH 25µA IQ

MP2192 Rev. 1.0

MonolithicPower.com

17

5/12/2021

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© 2021 MPS. All Rights Reserved.

The worst-case condition occurs at VIN = 2VOUT,

calculated with Equation (6):

LOAD

C1

I

I

2



(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, add a small, high-quality,

0.1μF ceramic capacitor 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 the capacitance can be

estimated with Equation (7):

LOAD

OUT

OUT

IN

IN

SW

IN

I

V

V

V1

f

C1

V

V



















(7)

Selecting the Output Capacitor

The output capacitor (C2) stabilizes the DC

output voltage. Low-ESR ceramic capacitors

are recommended to limit the output voltage

ripple. Estimate the output voltage ripple with

Equation (8):

OUT

OUT

OUT

ESR

SW

1

IN

SW

VV

1

V

1

R

f

L

V

8 f

C2



























 

(8)

Where L1 is the inductor value, and RESR is the

equivalent series resistance (ESR) value of the

output capacitor.

When

using

ceramic

capacitors,

the

capacitance dominates the impedance at the

switching frequency and causes most of the

output voltage ripple. For simplification, the

output voltage ripple can be estimated with

Equation (9):

OUT

OUT

OUT

2

SW

1

IN

VV

ΔV1

8 f

L

C2

V





 





 



(9)

For tantalum or electrolytic capacitors, the ESR

dominates the impedance at the switching

frequency. For simplification, the output ripple

can be calculated with Equation (10):

OUT

OUT

OUT

ESR

IN

SW

1

VV

ΔV

1

R

f

L

V





 









(10)

The characteristics of the output capacitor also

affect the stability of the regulation system.

Design Example

Table 3 lists a design example following the

application guidelines for the specifications

below.

Table 3: Design Example

VIN

5V

VOUT

1.2V

fSW

1100kHz

For the detailed application schematic, see

Figure

11

on

page

19.

For

the

typical

performance and circuit waveforms, see the

Typical Performance Characteristics section on

page 6. For more device applications, refer to

the related evaluation board datasheets.