MP2624GL datasheet(41/45 Pages) MPS

41 / 45 page

MP2624 – 4.5A SW CHARGER W/ I2C CONTROL, NVDC POWER PATH, USB OTG

MP2624 Rev.1.05

www.MonolithicPower.com

4/9/2018

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

APPLICATION INFORMATION

Component Selection

Setting the Input Current Limit

The input current limit setting is set according to

the input power source. For an adapter input, the

input current limit can be set through I2C by the

GUI. To set a value that is not provided by the

I2C, the input current limit can be set through

ILIM. Connect a resistor from ILIM to AGND to

program the input current limit. The relationship

is calculated using Equation (3):

）

（

）

（

ILIM

IN_LMT



(3)

The MP2624 selects the lower one of the I2C and

resistor setting for its input current limit setting.

For resistor setting, use 1% accuracy resistor.

For a USB input, the input current limit is set

according to Table 2.

Selecting the Inductor

Inductor selection is a trade off between cost,

size, and efficiency. A lower inductance value

corresponds to a smaller size, but it results in a

higher

ripple

current,

higher

magnetic

hysteretic loss, and a higher output capacitance.

Choosing a higher inductance value gives the

benefit of a lower ripple current and smaller

output filter capacitors, but it may result in higher

inductor DC resistance (DCR) loss and larger

size.

From a practical standpoint, the inductor ripple

current should not exceed 30% of the maximum

load current under worst-case conditions. When

operating with a typical 5V input voltage, the

maximum inductor current ripple occurs at the

corner point between the trickle charge and the

CC charge (VBATT = 3V). Estimate the required

inductance with Equation (4) and Equation (5):

)

(

MHz

BATT

MAX

BATT









(

H)

(4)

)

ripple

(

)

MAX

(

LOAD

PEAK







(A)

(5)

Where, VIN, VBATT, and fS are the typical input

voltage, battery voltage, and switching frequency,

respectively.

∆IL_MAX is the maximum inductor

ripple current, which is usually 30% of the CC

charge current.

Although the maximum charge current can be set

to a high 4.5A, the real charge current cannot

reach this value as the input current limit. For

most applications, allow a large enough margin

to avoid hitting the peak current limit of the high-

side switch (7A, typically). The maximum inductor

current ripple is set to 1.0A with 5Vin (30% of the

max load- about 3.5A considering the input

current limit); the inductor is 0.75µH. Select

1.0µH in the application with the saturation

current over 4.5A Select 1.0µH in the application

with the saturation current over 4.5A

Choose a larger inductance such as 2.2uH is

good for the EMI consideration with smaller

current ripple, while the size may be larger.

Selecting the Input Capacitor

The input current to the step-down converter is

discontinuous, therefore a capacitor is required to

supply the AC current to the step-down converter

while maintaining the DC input voltage. Use low

ESR capacitors for the best performance.

Ceramic capacitors are preferred, but tantalum or

low ESR electrolytic capacitors will suffice.

Choose X5R or X7R dielectrics when using

ceramic capacitors.

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 (6):















OUT

CLOAD

(6)

Where, VOUT is VSYS.

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

where ICIN = ILOAD/2. For simplification, choose the

input capacitor with a RMS current rating greater

than half of the maximum load current.

For the MP2624, the RMS current in the input

capacitor comes from PMID to GND, so a small,

high-quality ceramic capacitor (e.g., 4.7μF),

should be placed as close to the IC as possible

from VPMID to PGND. The remaining capacitor

should be placed from VIN to GND.

MP2624GL 数据表(PDF) 41 Page - Monolithic Power Systems

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