BD9302FP-E Datasheet, PDF(9/17 Page) Rohm – A wide input voltage range of 6 V to 18 V, Easy switching frequency setting in the range of 200 k to 2.5 MHz.

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BD9302FP-E Datasheet, PDF (9/17 Pages) Rohm – A wide input voltage range of 6 V to 18 V, Easy switching frequency setting in the range of 200 k to 2.5 MHz.

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External component setting procedure

(1) Setting of output L constant

The coil L used for output is determined according to the rated current ILR and the maximum load current value IOMAX

of the coil.

Adjust so that (IOMAX + DIL) will

VCC

not conflict with the rating.

ILR

Average IOMAX current

Fig.22

Fig.23

Adjust so that (IOMAX + DIL) will not conflict with the rating. At this time, DIL can be obtained according to the formula

shown below.

Step-down DIL =

Â¥ (VCC â VO) Â¥

VCC

Â¥

[A] . . . (1.1)

,where f: Switching frequency

Furthermore, since the coil L value may also vary by approximately Â±30%, set this value with an adequate margin. If the

coil current IL exceeds the rated coil current ILR, the internal IC element may be damaged. It is recommended to make

setting of coil value in the range of 4.7 Î¼F to 100 Î¼F.

(2) Setting of output Co constant

For output capacitor, select the allowable ripple voltage VPP or the allowable drop voltage at a sharp change of load,

whichever larger for the capacitor. The output ripple voltage can be obtained according to the formula shown below.

Step-down

DVPP = DIL Â¥ RESR +

DIL

2CO

Â¥

VCC

Â¥

[V]

,where f: Switching frequency

Design the component so that this constant will fall within the allowable ripple voltage.

Furthermore, estimate the drop voltage VDR at a sharp change of load according to the formula shown below.

VDR =

Â¥ 10Î¼sec

[V]

However, 10 Î¼sec will be the estimated value of the DC/DC converter response speed.

Make setting of capacitance with thorough consideration given to the margin so that these two values will fall into the

specified values. It is recommended to make setting of the capacitance in the range of 10 Î¼F to 100 Î¼F. if a short circuit

occurs, an inverse current passes through the parasitic diode to cause damage to the internal circuits. To prevent that,

insert a backflow prevention diode.

9/16

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