ADPL74101 datasheet(27/49 Pages) AD

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Data Sheet

ADPL74101

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Rev. 0

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Setting the Operating Frequency

Selecting the operating frequency is a trade-off between efficiency and component size. High-frequency operation

allows the use of smaller inductor and capacitor values. Operation at lower frequencies improves efficiency by

reducing gate charge and transition losses, but requires larger inductance values and/or more output capacitance

to maintain low output ripple voltage.

In higher voltage applications, transition losses contribute more significantly to power loss, and a proper balance

between size and efficiency is achieved with a switching frequency between 300kHz and 900kHz. Lower-voltage

applications benefit from lower switching losses, and can operate at switching frequencies up to 1MHz, if desired.

The switching frequency is set using the FREQ and PLLIN/SPREAD pins, as shown in Table 4.

Table 4. Setting the Switching Frequency Using FREQ and PLLIN/SPREAD

FREQ PIN

PLLIN/SPREAD PIN

FREQUENCY

370kHz

Resistor to GND

100kHz to 1MHz

Any of the Above

External Clock, 100kHz to 1MHz

Phase-locked to external clock

Any of the Above

INTVCC

Spread spectrum fOSC modulated 0% to +20%

Tying the FREQ pin to ground selects 370kHz. Placing a resistor between FREQ and ground allows the frequency to

be programmed anywhere between 100kHz and 1MHz. Choose a FREQ pin resistor (RFREQ) from Figure 32 or Equation

9, as follows:

RFREQ(in kΩ) =

37MHz

fosc

(9)

Figure 32. Relationship Between Oscillator Frequency and Resistor Value at the FREQ Pin

To improve EMI performance, the spread-spectrum mode can be selected by tying the PLLIN/SPREAD pin to INTVCC.

When spread spectrum mode is enabled, the switching frequency modulates around the frequency selected by the

FREQ pin, and +20%. Spread-spectrum mode can be used in any operating mode selected by the MODE pin (Burst

Mode, pulse-skipping, or forced continuous mode).

FREQ PIN RESISTOR (Ω)

40k

100k

500k

100k

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