Data Sheet

ADPL76030

analog.com

Rev.0

25 of 40

APPLICATIONS INFORMATION

Figure 1 shows a typical ADPL76030 application circuit. This section serves as a guideline to select external

components for typical applications. The examples and equations in this section assume continuous conduction

mode, unless otherwise specified.

Switching Frequency Selection

The ADPL76030 uses a constant frequency control scheme between 600 kHz and 1.4 MHz. Selection of the switching

frequency is a trade-off between efficiency and component size. Low frequency operation improves efficiency by

reducing MOSFET switching losses, but requires larger inductor and capacitor values. For high power applications,

consider operating at lower frequencies to minimize MOSFET heating from switching losses. For low power

applications, consider operating at higher frequencies to minimize the total solution size.

In addition, the specific application also plays an important role in switching frequency selection. In a noise-sensitive

system, the switching frequency is usually selected to keep the switching noise out of a sensitive frequency band.

Switching Frequency Setting

The switching frequency of the ADPL76030 can be set by the internal oscillator. With the SYNC/SPRD pin pulled to

ground, the switching frequency is set by a resistor from the RT pin to ground. Table 5 shows RT resistor values for

common switching frequencies.

Table 5. RT Resistor Values for Common Switching Frequencies

fOSC (MHz)

RT (k)

0.6

267

0.8

191

1.0

147

1.2

118

1.4

97.6

Spread Spectrum Frequency Modulation

Switching regulators can be particularly troublesome for applications where electromagnetic interference (EMI) is a

concern. To improve the EMI performance, the ADPL76030 implements a triangle spread spectrum frequency

modulation scheme. With the SYNC/SPRD pin tied to INTVCC, the ADPL76030 starts to spread its switching frequency

25% above the internal oscillator frequency. Figure 43 and Figure 44 show the noise spectrum of the front-page

application when spread spectrum is enabled.