BL3406B-15CRN 데이터 시트보기 (PDF) - Shanghai Belling Co., Ltd.

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BL3406B-15CRN

1.5 MHz, 800mA Synchronous Buck Converter

Shanghai Belling Co., Ltd. 

BL3406B

1.5 MHz, 800mA Synchronous Buck Converter

Application Information

Figure 2 below shows the basic application

circuit with BL3406B fixed output versions.

2.7V - 4.2V

VIN

C1

4.7uF

4 VIN

L1

SW 3 2.2µH

BL3406B-18

1 Run

VOUT 5

GND

2

VOUT1.8V

C2

10uF

Figure 2. Basic Application Circuit

with fixed output versions

Setting the Output Voltage

Figure 1 above shows the basic application

circuit with BL3406B adjustable output

version. The external resistor sets the output

voltage according to the following equation:

VOUT

= 0.6V × (1 +

R2)

R1

Table 1—Resistor Selection vs.

Output Voltage Setting

VOUT

R1

R2

1.0V

180 kΩ(1%) 120 kΩ(1%)

1.2V

180 kΩ(1%) 180 kΩ(1%)

1.5V

180 kΩ(1%) 270 kΩ(1%)

1.8V

180 kΩ(1%) 360 kΩ(1%)

2.5V

158 kΩ(1%) 499 kΩ(1%)

3.3V

180 kΩ(1%) 810 kΩ(1%)

Inductor Selection

The output inductor is selected to limit the

ripple current to some predetermined value,

typically 20%~40% of the full load current at

the maximum input voltage. In continuous

mode, the ripple current is determined by:

∆I L =

f

1

×

L VOUT

(1− VOUT

VIN

)

A reasonable starting point for setting ripple

current is ∆IL=320mA (40% of 800mA). For

output voltages above 2.0V, when efficiency

at light load condition is important, the

minimum recommended inductor is 2.2µH.

For optimum voltage-positioning load

transients, choose an inductor with DC series

resistance below 150mΩ. For higher

efficiency at heavy loads (above 200mA), or

minimal load regulation (but some transient

overshoot), the resistance should be kept

below 100mΩ. The DC current rating of the

inductor should be at least equal to the

maximum load current plus half the ripple

current to prevent core saturation. Thus, a

1120mA rated inductor should be enough for

most applications (800mA+320mA).

Input Capacitor Selection

The input capacitor reduces the surge current

drawn from the input and switching noise

from the device. The input capacitor

impedance at the switching frequency shall

be less than input source impedance to

prevent high frequency switching current

passing to the input. In continuous mode, the

source current of the main switch is a square

wave of duty cycle VOUT/VIN. To prevent large

voltage transients, a low ESR input capacitor

sized for the maximum RMS current must be

used. The maximum RMS capacitor current is

given by:

I RMS

≈

I OMAX

[VOUT (VIN −VOUT )]0.5

VIN

This formula has a maximum at VIN =2VOUT,

where IRMS = IOUT/2. This simple worst-case

condition is commonly used for design

because even significant deviations do not

offer much relief. Ceramic capacitors with

X5R or X7R dielectrics are recommended

due to their low ESR and high ripple current.

Output Capacitor Selection

The output capacitor is required to keep the

output voltage ripple small and to ensure

regulation loop stability. The output capacitor

must have low impedance at the switching

PPMIC BU

www.belling.com.cn

8

BL3406B Rev 1.5

Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited

10/2009

©2009 Belling All Rights Reserved

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