MP2624GL datasheet(42/45 Pages) MPS

42 / 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.

When using ceramic capacitors, make sure they

have enough capacitance to provide sufficient

charge to prevent excessive voltage ripple at the

input.

Selecting the Output Capacitor

The output capacitor CSYS from the typical

application circuit is in parallel with the SYS load.

CSYS absorbs the high-frequency switching ripple

current and smoothes the output voltage. Its

impedance must be much less than the system

load to ensure it properly absorbs the ripple

current.

Use a ceramic capacitor because it has a lower

ESR and a smaller size. This allows the ESR of

the output capacitor to be ignored. Thus, the

output voltage ripple is given with Equation (7):













SYS

V8 C

(7)

In order to guarantee ±0.5% system voltage

accuracy, the maximum output voltage ripple

must not exceed 0.5% (e.g. 0.1%). The

maximum output voltage ripple occurs at the

minimum system voltage and the maximum input

voltage.

For VIN = 7V, VSYS_MIN = 3.6V, L = 2.2µH, fS =

1.6MHz, and

r =0.1%. The output capacitor can

be calculated as 11µF using Equation (8):





  

SYS _ MIN

SYS

(8)

Then, choose a 22µF ceramic capacitor.

Resistor Selection for the NTC Sensor

Figure 9 shows an internal resistor divider

reference circuit that limits both the high and low

temperature thresholds at VTH_High and VTH_Low,

respectively. For a given NTC thermistor, select

an appropriate RT1 and RT2 to set the NTC

window using Equation (9) and Equation (10):

NTC_Cold

TH_Low

NTC_Cold

NTC

R//R

RR //R





(9)

TH_High

NTC_Hot

R//R

R //R

VCC





(10)

RNTC_Hot is the value of the NTC resistor at a high

temperature (within the required temperature

operating range), and RNTC_Cold is the value of the

NTC resistor at a low temperature.

The two resistors (RT1 and RT2) allow the high and

low temperature limits to be programmed

independently. With this feature, the MP2624 can

fit most types of NTC resistors and different

temperature operating range requirements.

RT1 and RT2 values depend on the type of the

NTC resistor selected.

For example, for a 103AT thermistor, the

thermistor

has

the

following

electrical

characteristics:

At 0°C, RNTC_Cold = 27.28kΩ;

at 60°C, RNTC_Hot = 3.02kΩ.

The following equation calculations are derived

assuming that the NTC window is between 0°C

and 50°C. According to Equation (9) and

Equation (10), use

TH_Low

NTC

and

TH_High

NTC

from the

EC table to calculate RT1 = 2.27kΩ and RT2 =

6.86kΩ.

MP2624GL 数据表(PDF) 42 Page - Monolithic Power Systems

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