MP2733 datasheet(46/51 Pages) MPSIND

46 / 51 page

MP2733

– 4.5A SW CHARGER WITH I2C CONTROL, NVDC POWER PATH, USB OTG

MP2733 Rev. 1.1

www.MonolithicPower.com

5/18/2023

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

APPLICATION INFORMATION

Setting the Input Current Limit

The input current limit (IIN_LIM) is set according to

the input power source. IIN_LIM can be set through

the I2C using the MP2733

’s GUI. If a user wants

to set a current limit that cannot be set by the I2C,

it can be set using the ILIM pin. Connect a

resistor from the ILIM pin to AGND to program

IIN_LIM. The MP2733 selects the lower value

between the I2C setting and the resistor setting.

The ILIM pin resistance can be calculated with

Equation (1) on page 22.

See Table 1 on page 22 to determine how to set

IIN_LIM for USB inputs.

Selecting the Inductor

Inductor selection is a tradeoff between cost,

size, and efficiency. A smaller-value inductor is

physically small, but results in higher ripple

current, magnetic hysteretic loss, and output

capacitance. A larger-value inductor provides

lower ripple current and smaller output filter

capacitors, but results in higher inductor DC

resistance (DCR) loss.

For the best results, the inductor ripple current

should not exceed 30% of the maximum load

current under the worst-case conditions. For the

MP2733 to operate with a typical 5V input

voltage, the maximum inductor current ripple

occurs at the corner point between pre-charge

and constant current charge. The inductance (L)

can be estimated with Equation (2):

SYS

L_MAX

V -V

(

μH)

ΔI

(MHz)



(2)

Where VIN is the input voltage, VSYS is the system

voltage, fSW is the switching frequency, and

∆IL_MAX is the maximum inductor ripple current,

(usually 30% of the CC charge current).

IPEAK can be calculated with Equation (3):

L_MAX

PEAK

LOAD(MAX)

= I

(1+

)(A)





(3)

The maximum charge current can be set to 4.5A,

but the real charge current cannot reach this

value due to the input current limit. For typical

applications, the maximum inductor current

ripple is set to 0.5A with a 5V input voltage, and

the inductance is 1.5µH. Select a 1µH inductor

for low-profile operation.

To optimize efficiency, choose an inductor with a

low DC resistance.

Selecting the Input Capacitor

The converter has a discontinuous input current,

and requires a capacitor to supply the AC current

to the converter while maintaining the DC input

voltage. Use low-ESR capacitors for the best

performance.

Ceramic

capacitors

are

recommended,

but

tantalum

low-ESR

electrolytic capacitors are sufficient.

Choose

ceramic capacitors with X5R or X7R dielectrics.

Since the input capacitor (CIN) absorbs the input

switching current, it requires an adequate ripple

current rating. The RMS current in the input

capacitor can be estimated with Equation (4):













−

SYS

CIN

LOAD

(4)

The worst-case condition occurs when VIN =

2VSYS, and ICIN = ISYS / 2. For simplification,

choose an input capacitor with an RMS current

rating that exceeds half of the maximum load

current.

For the MP2733, the RMS current in the input

capacitor is from PMID to GND. This means a

small, high-quality ceramic capacitor (e.g. 10

μF)

should be placed from VPMID to PGND, as close

to the IC as possible. The remaining capacitor

should be placed from VIN to GND.

When using ceramic capacitors, ensure that they

have enough capacitance to provide a sufficient

charge that prevents excessive voltage ripple at

the input.

Selecting the Output Capacitor

In the typical application circuit, the output

capacitor (CSYS) is in parallel with the SYS load.

CSYS absorbs the high-frequency switching ripple

current and smooths the output voltage. Its

impedance must be below that of the system

load to ensure that it properly absorbs the ripple

current.

It is recommended to use a ceramic capacitor

because its lower ESR and smaller size allow the

ESR of the output capacitor to be ignored.

MP2733 Datasheet(PDF) 46 Page - MPS Industries, Inc.

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