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Fabricante

ISL6315
(Rev.:2006)

Two-Phase Multiphase Buck PWM Controller with Integrated MOSFET Drivers

Intersil 

ISL6315

maximum input voltage. The input RMS current required for

a multiphase converter can be approximated with the aid of

Figure 12.

0.3

0.2

0.1

IL,P-P = 0

IL,P-P = 0.5 x IO

IL,P-P = 0.75 x IO

0

0

0.1

0.2

0.3

0.4

0.5

DUTY CYCLE (VO /VIN)

FIGURE 12. NORMALIZED INPUT RMS CURRENT vs DUTY

CYCLE FOR A 2-PHASE CONVERTER

As the input capacitors are responsible for sourcing the AC

component of the input current flowing into the upper

MOSFETs, their RMS current capacity must be sufficient to

handle the AC component of the current drawn by the upper

MOSFETs. Figure 12 can be used to determine the input-

capacitor RMS current function of duty cycle, maximum

sustained output current (IO), and the ratio of the peak-to-

peak inductor current (IL,P-P) to the maximum sustained

load current, IO. Figure 12 can also be used as a reference

demonstrating the dramatic reduction in input capacitor RMS

current in a 2-phase DC/DC converter, as compared to a

single-phase regulator.

Use a mix of input bypass capacitors to control the input

voltage ripple. Use ceramic capacitance for the high

frequency decoupling and bulk capacitors to supply the

RMS current. Minimize the connection path inductance of

the high frequency decoupling ceramic capacitors (from

drain of upper MOSFET to source of lower MOSFET).

For bulk capacitance, several electrolytic or high-capacity MLC

capacitors may be needed. For surface mount designs, solid

tantalum capacitors can be used, but caution must be

exercised with regard to the capacitor surge current rating.

These capacitors must be capable of handling the surge-

current at power-up.

19

FN9222.0

February 10, 2006

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