High Efficiency 1.5MHz, Step up Regulator

EC9211

Page 14 of 15

3G24N-Rev.P001

Application Information(Cont.)

I Output Capacitor Selection (Cont.)

For ceramic capacitor application, the output voltage ripple is

dominated by the

ceramic capacitors, the X5R or X7R with their good temperature

and voltage characteristics are recommended.

Output Voltage Setting

The output voltage is set by a resistive divider. The external

resistive divider is connected to the output which allows remote

voltage sensing as shown in

“Typical Application Circuits”. A

suggestion of the maximum value of R1 is 2M

Ω and R2 is

200k

Ω for keeping the minimum current that provides enough

noise rejection ability through the resistor divider. The output

voltage can be calculated as below:

Diode Selection

To achieve the high efficiency, a Schottky diode must be used.

The current rating of the diode must meet the peak current rating

of the converter.

Layout Consideration

For all switching power supplies, the layout is an important step in

the design especially at high peak currents and switching

frequencies. If the layout is not carefully done, the regulator might

show noise problems and duty cycle jitter.

1. The input capacitor should be placed close to the VIN and the

GND without any via holes for good input voltage filtering.

2. To minimize copper trace connections that can inject noise into

the system, the inductor should be placed as close as possible to

the LX pin to minimize the noise coupling into other circuits.

3. Since the feedback pin and network is a high impedance circuit

the feedback network should be routed away from the inductor.

The feedback pin and feedback network should be shielded with a

ground plane or trace to minimize noise coupling into this circuit.

4. A star ground connection or ground plane minimizes ground

shifts and noise is recommended.