MP4572

– 60V, 2A, SYNCHRONOUS STEP-DOWN CONVERTER

MP4572 Rev. 1.0

www.MonolithicPower.com

27

3/9/2020

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

© 2020 MPS. All Rights Reserved.

The worst case condition occurs at VIN = 2VOUT,

calculated with Equation (6):

OUT

CIN

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, use a small, high-quality ceramic

capacitor (0.1μF), placed as close to the IC as

possible. The input capacitance value determines

the input voltage ripple of the converter. If there

is an input voltage ripple requirement in the

system design, choose an input capacitor that

meets the specification.

The

input

voltage

ripple

caused

by

the

capacitance can be estimated with Equation (7):







 



OUT

OUT

OUT

IN

SW

IN

IN

IN

I

V

V

V

(1

)

f

C

V

V

(7)

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

estimated with Equation (8):



 



OUT

IN

SW

IN

I

1

V

4

f

C

(8)

Selecting the Output Capacitor

The output capacitor maintains the output DC

voltage. Ceramic capacitors with low ESR are

recommended for their small size and low output

voltage

ripple.

Electrolytic

and

polymer

capacitors may also be used. The output voltage

ripple can be estimated with Equation (9):

OUT

OUT

OUT

ESR

SW

IN

SW

OUT

VV

1

V

(1

) (R

)

f

L

V

8f

C





 







(9)

Where RESR is the equivalent series resistance of

the output capacitor.

For

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 calculated with Equation (10):





 



 

OUT

OUT

OUT

2

SW

OUT

IN

VV

V

(1

)

8 f

L C

V

(10)

For tantalum or electrolytic capacitors, the ESR

dominates

the

impedance

at

the

switching

frequency. For simplification, the output ripple

can be calculated with Equation (11):





 





OUT

OUT

OUT

ESR

SW

IN

VV

V

(1

) R

f

L

V

(11)

Another consideration for the output capacitance

is the allowable overshoot in VOUT if the load is

suddenly removed. In this case, energy stored in

the inductor is transferred to COUT, causing its

voltage to rise. To achieve a desired overshoot

relative to the regulated voltage, the output

capacitance can be estimated with Equation (12):







2

OUT

OUT

22

OUT

OUTMAX

OUT

IL

C

V

((V

/ V

)

1)

(12)

Where VOUTMAX / VOUT is the allowable maximum

overshoot.

After calculating the capacitance required for

both the ripple and overshoot, choose the larger

value.

The characteristics of the output capacitor also

affect the stability of the regulation system. The

MP4572 can be optimized for a wide range of

capacitance and ESR values.

VIN Under-Voltage Lockout (UVLO) Setting

The MP4572 has an internal, fixed under-voltage

lockout (UVLO) threshold. The rising threshold is

4.0V, while the falling threshold is about 3.5V.

For applications that require a higher UVLO point,

place an external resistor divider between EN

and IN to obtain a higher equivalent UVLO

threshold (see Figure 5 and Figure 6). Add a 6V

Zener diode between EN to GND if the EN pin is

connected to VIN through a resistor.

VIN

EN

IN

R4

1.8M

Ω

R5

8

12

6V

Zener

Figure 5: Adjustable UVLO using EN Divider

when EN Rises