DUAL CHANNEL1.5 MHZ, 600MA SYNCHRONOUS STEP-DOWN CONVERTER

2007-7-11

7/10

FSP3112

APPLICATION INFORMATION

Fig.1 FSP3112 Typical Application Circuit

SETTING THE OUTPUT VOLTAGE

The external resistor sets the output voltage according to the following equation:

OUT

R2

V0.6V 1+

R1

⎛⎞

=

⎜⎟

⎝⎠

Table 1 ----Resistor select for output voltage setting

R1(R3)

R2(R4)

1.2V

316K

316K

1.5V

316K

474K

1.8V

316K

634K

2.5V

316K

1001K

INDUCTOR SELECTION

For most designs, the FSP3112 operates with inductors of 1µH to 4.7µH. Low inductance values are physically

smaller but require faster switching, which results in some efficiency loss. The inductor value can be derived from

the following equation:

()

OUT

IN

OUT

IN

L

OSC

VV

V

L

VI

f

×−

=

×∆ ×

high ripple currents. Choose inductor ripple current approximately 35% of the maximum load current 600mA, or

For output voltages above 2.0V, when light-load efficiency is important, the minimum recommended inductor is

2.2µH. For optimum voltage-positioning load transients, choose an inductor with DC series resistance in the 50mΩ

to 150mΩ range. For higher efficiency at heavy loads (above 200mA), or minimal load regulation (but some transient

overshoot), the resistance should be kept below 100mΩ. The DC current rating of the inductor should be at least

equal to the maximum load current plus half the ripple current to prevent core saturation (600mA+105mA). Table2

lists some typical surface mount inductors that meet target applications for the FSP3112.