MP2328 – 28V, 2A, SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS

MP2328 Rev. 1.0

www.MonolithicPower.com

17

12/11/2020

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APPLICATION INFORMATION

Setting the Output Voltage

The external resistor divider sets the output

voltage. Choose a value for R2. R2 should be

chosen reasonably, as a smaller-value resistor

results in considerable quiescent current loss,

while a larger-value resistor makes FB sensitive

to noise. Typically, set the current through R2 to

be between 5µA and 50µA for an optimal

balance between system stability and no-load

loss. Then R1 can be calculated with Equation

(4):

OUT

REF

REF

VV

R1

R2

V





(4)

Figure 3 shows the feedback circuit. RT is an

optional resistor for feedback compensation.

MP2328

FB

R1

R2

VOUT

RT

CFF

Figure 3: Feedback Network

Table 1 lists the recommended parameters for

common output voltages.

Table 1: Parameter Selection for Common

Output Voltages

VOUT

(V)

R1

(kΩ)

R2

(kΩ)

RT

(kΩ)

CFF

(pF)

L

(μH)

1

51

51

10

82

3.3

1.8

51

16.9

10

470

4.7

2.5

51

12.7

10

470

6.8

3.3

51

9.09

10

470

10

5

90.9

10

10

300

10

12

255

11

10

82

15

Selecting the Inductor

The inductor must 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 a lower output

ripple voltage. However, a larger-value inductor

has a larger physical footprint, higher series

resistance, and lower saturation current. The

inductance value can be calculated with

Equation (5):

OUT

OUT

sw

L

IN

VV

L=

(1-

)

fI

V





(5)

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 estimated with Equation

(6):

OUT

OUT

LP

OUT

sw

IN

VV

I=I

(1-

)

2f

L

V





(6)

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-AL

2.2µH to

15µH

MPS

MPL-AL-6050-3R3

3.3μH

MPS

MPL-AL-6060-4R7

4.7μH

MPS

MPL-AL6060-6R8

6.8μH

MPS

MPL-AL6060-100

10μH

MPS

MPL-AL6060-150

15μH

MPS

Visit MonolithicPower.com under Products >

Inductors for more information.

Selecting the Input Capacitor

The step-down converter has a discontinuous

input current, and requires a capacitor to supply

the

AC

current

to

the

converter

while

maintaining the DC input voltage. Ceramic

capacitors are recommended for the best

performance, and they should be placed as

close to the VIN pin as possible. Capacitors

with

X5R

and

X7R

dielectrics

are

recommended because they are fairly stable

with temperature fluctuations.

The capacitors must also have a ripple current

rating greater than the maximum input ripple

current of the converter.