Document Number: 002-09201 Rev. *C

Page 13 of 36

MB39C006A

10. Application Notes

10.1 Selection of Components

Basically it dose not need to design inductor. The MB39C006A is designed to operate efficiently with a 2.2 µH (2.0 MHz operation) or

1.5 µH (3.2 MHz operation) external inductor.

The inductor should be rated for a saturation current higher than the LX peak current value during normal operating conditions, and

should have a minimal DC resistance. (100 mΩ or less is recommended.)

L : External inductor value

D : ON- duty to be switched(

fosc : Switching frequency (2.0 MHz or 3.2 MHz)

currents on the output capacitor which, in turn, causes ripple voltages an output equal to the amount of variation multiplied by the

ESR value. The output capacitor value has a significant impact on the operating stability of the device when used as a DC/DC

converter. Therefore, Cypress generally recommends a 4.7 µF capacitor, or a larger capacitor value can be used if ripple voltages

Ceramic capacitors are effective for reducing the ESR and afford smaller DC/DC converter circuit. However, power supply functions

as a heat generator, therefore avoid to use capacitor with the F-temperature rating

(

Normal electrolytic capacitors are not recommended due to their high ESR.

Tantalum capacitor will reduce ESR, however, it is dangerous to use because it turns into short mode when damaged. If you insist

on using a tantalum capacitor, Cypress recommends the type with an internal fuse.

10.2 Output Voltage Setting

from an external power supply, or set the VREF output by dividing it with resistors.

The output voltage when the VREFIN voltage is set by dividing the VREF voltage with resistors is shown in the following formula.

×

D

×

1

Lfosc

2

2

(3.7 V

≈ 0.89 A

2

2

R4

R3