BD9011EKN 查看數據表（PDF） - ROHM Semiconductor

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BD9011EKN

Dual-output, high voltage, high-efficiency step-down Switching Regulator (Controller type)

ROHM Semiconductor 

●Application component selection

(1) Setting the output L value

ΔIL

Fig-17

VCC

IL

L

VOUT

Co

Fig-18

Output ripple current

The coil value significantly influences the output ripple current.

Thus, as seen in equation (5), the larger the coil, and the higher

the switching frequency, the lower the drop in ripple current.

ΔIL = （VCC-VOUT）×VOUT [A]・・・（5）

L×VCC×f

The optimal output ripple current setting is 30% of maximum current.

ΔIL = 0.3×IOUTmax.[A]・・・（6）

L = （VCC-VOUT）×VOUT [H]・・・（7）

ΔIL×VCC×f

（ΔIL：output ripple current f：switching frequency）

※Outputting a current in excess of the coil current rating will cause magnetic saturation of the coil and decrease

efficiency.

Please establish sufficient margin to ensure that peak current does not exceed the coil current rating.

※Use low resistance (DCR, ACR) coils to minimize coil loss and increase efficiency.

(2) Setting the output capacitor Co value

Select the output capacitor with the highest value for ripple voltage (VPP) tolerance and maximum drop voltage

(at rapid load change). The following equation is used to determine the output ripple voltage.

ΔIL

Vo

1

Step down ΔVPP = ΔIL × RESR +

×

×

[V]

Co

Vcc

f

Note: f：switching frequency

Be sure to keep the output Co setting within the allowable ripple voltage range.

※Please allow sufficient output voltage margin in establishing the capacitor rating. Note that low-ESR capacitors enable

lower output ripple voltage.

Also, to meet the requirement for setting the output startup time parameter within the soft start time range, please factor

in the conditions described in the capacitance equation (9) for output capacitors, below.

TSS × (Limit – IOUT)

Co ≦

VOUT

・・・ （9）

Tss： soft start time

ILimit：over current detection value（2/16）reference

Note: less than optimal capacitance values may cause problems at startup.

(3) Input capacitor selection

VIN

Cin

L

VOUT

Co

Fig-19

Input capacitor

The input capacitor serves to lower the output impedance of the power

source connected to the input pin (VCC). Increased power supply output

impedance can cause input voltage (VCC) instability, and may negatively

impact oscillation and ripple rejection characteristics. Therefore, be

certain to establish an input capacitor in close proximity to the VCC and

GND pins. Select a low-ESR capacitor with the required ripple current

capacity and the capability to withstand temperature changes without

wide tolerance fluctuations. The ripple current IRMSS is determined

using equation (10).

IRMS = IOUT × VOUT（VCC - VOUT） [A]・・・（10）

VCC

Also, be certain to ascertain the operating temperature, load range and

MOSFET conditions for the application in which the capacitor will be used,

since capacitor performance is heavily dependent on the application’s

input power characteristics, substrate wiring and MOSFET gate drain

capacity.

8/28

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