BD8158FVM(2010) Ver la hoja de datos (PDF) - ROHM Semiconductor

Número de pieza

componentes Descripción

Fabricante

BD8158FVM
(Rev.:2010)

High-efficiency Step-up Switching Regulators with Built-in Power MOSFET

ROHM Semiconductor 

BD8152FVM, BD8158FVM

Technical Note

Selecting Application Components

(1) Setting the output L constant

The coil L to use for output is decided by the rating current ILR and input current maximum value IINMAX of the coil.

IL

IINMAX + IL should not

VCC

reach the rating value level

L

IL

ILR

IINMAX average

Vo

current

Co

t

Fig. 23 Coil current waveform

Fig. 24 Output Application Circuit Diagram

Adjust so that IINMAX + ∆IL does not reach the rating current value ILR. At this time, ∆IL can be obtained by the following

equation.

1

Vo - Vcc

1

∆IL= L Vcc 

Vo

f

[A] Where, f is the switching frequency.

Set with sufficient margin because the coil L value may have the dispersion of approx. 30%. If the coil current exceeds

the rating current ILR of the coil, it may damage the IC internal element.

BD8152FVM,BD8158FVM use the current mode DC/DC converter control and has the optimized design at the coil value.

The following coil values are recommended from the aspects of power efficiency, response and safety. When the coil out

of this range is selected, the stable continual operation is not guaranteed such as the switching waveform becomes

irregular. Please pay attention to it.

Switching frequency: L = 10 uH to 22 uH at 600 kHz

Switching frequency: L = 4.7 uH to 15 uH at 1,200 kHz

(2) Setting the output capacitor

For the capacitor C to use for the output, select the capacitor which has the larger value in the ripple voltage VPP

allowance value and the drop voltage allowance value at the time of sudden load change. Output ripple voltage is

decided by the following equation.

∆VPP

= ILMAX  RESR + 1  Vcc  (ILMAX -

fCo

Vo

∆IL )

2

[V] Where, f is the switching frequency.

Perform setting so that the voltage is within the allowable ripple voltage range.

For the drop voltage during sudden load change; VDR, please perform the rough calculation by the following equation.

VDR = ∆I

Co

 10u sec

[V]

However, 10 s is the rough calculation value of the DC/DC response speed. Please set the capacitance considering the

sufficient margin so that these two values are within the standard value range.

(3) Selecting the input capacitor

Since the peak current flows between the input and output at the DC/DC converter, a capacitor is required to install at the

input side. For this reason, the low ESR capacitor is recommended as an input capacitor which has the value more than

10μF and less than 100 mΩ. If a capacitor out of this range is selected, the excessive ripple voltage is superposed on the

input voltage, accordingly it may cause the malfunction of IC.

However these conditions may vary according to the load current, input voltage, output voltage, inductance and switching

frequency. Be sure to perform the margin check using the actual product.

www.rohm.com

© 2010 ROHM Co., Ltd. All rights reserved.

8/17

2010.03 - Rev.B

Share Link: