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A higher value of ripple current reduces inductance, but increases the conductance loss, core loss, and current

stress for the inductor and switch devices. It also requires a bigger output capacitor for the same output voltage ripple

requirement. A reasonable value is setting the ripple current to be 30% of the DC output current. Since the ripple

current increases with the input voltage, the maximum input voltage is always used to determine the inductance. The

DC resistance of the inductor is a key parameter for the efficiency. Lower DC resistance is available with a bigger

winding area. A good tradeoff between the efficiency and the core size is letting the inductor copper loss equal 2% of

the output power. A good starting point for most applications is a 4.7

μH to 15μH with 1A or greater current rating for

the

. Using such a rating will enable the

to current limit without saturating the inductor. This is

preferable to the

going into thermal shutdown mode and the possibility of damaging the inductor if the

output is shorted to ground or other long term overload.

Output Capacitor

The selection of Co is driven by the maximum allowable output voltage ripple. The output ripple in the constant

frequency, PWM mode is approximated by:

RIPPLE

RIPPLE

SW

1

V

=I

*(ESR +

)

8 * f *Co

The ESR term usually plays the dominant role in determining the voltage ripple. Low ESR ceramic capacitors are

recommended. Capacitors in the range of 22μF-100μF are a good starting point with an ESR of 0.1Ω orless.

Booststrap Capacitor

A 0.15μF ceramic capacitor or larger is recommended for the bootstrap capacitor (Cboot). For applications where

the input voltage is less than twice the output voltage a larger capacitor

is recommended, generally 0.15μF to 1μF to

Soft-Start

The built-in soft start, controlled by the clock signal frequency, in order to prevent the current overshoort when

opening.

Shutdown Operation

The EN pin of the

is designed so that it may be controlled using 1.5V or higher logic signals. If the

shutdown function is not to be used the EN pin may be tied to VIN with a resistor（A 1M

Ω or larger resistor is

recommended between the input voltage and the EN pin to protect the device.）. The maximum voltage to the EN pin

should not exceed 5V.

Schottky Diode

The breakdown voltage rating of the diode (D1) is preferred to be 25% higher than the maximum input voltage. The