3MHz 2.4A Synchronous Buck Converter

8

Theory of Operation / Application Information

Basic Operation

The operation of the controller consists of comparing the VFB voltage to an internal reference. When

the VFB voltage is lower than the VREF, the upper switch turns on. When the VFB voltage is higher

than VREF, the upper switch turns off and the lower switch turns on. An internal ramp is used to

stabilize the switching frequency and keep the VFB immune to the output capacitor, CO, value or

parasitic components (i.e. esr, esl).

In addition, a frequency control loop ensures the switching

frequency is constant under continuous conduction mode of operation.

At light load, the converter automatically reduces the switching frequency to optimize efficiency while

ensuring the ripple voltage is low.

Setting of the Output Voltage

The LX7167A develops a 0.6V reference voltage between the feedback pin, FB, and the signal

ground. The output voltage is set by a resistive divider according to the following formula:

(

)

The output component values are recommended below.

VOUT

L

R1

R2

COUT

C9

5V input

3.3V input

1V

0.47μH &

0.68μH

66.5kΩ

100kΩ

22μF

10pF

2x22μF

15pF

4x22μF

22pF

1.0μH

22μF

15pF

12pF

2x22μF

22pF

22pF

4x22μF

27pF

27pF

1.8V

0.47μH &

0.68μH

100kΩ

49.9kΩ

22μF

10pF

2x22μF

15pF

4x22μF

22pF

1.0μH

22μF

15pF

2x22μF

22pF

4x22μF

27pF

2.5V

0.47μH &

0.68μH

158kΩ

49.9kΩ

22μF

15pF

2x22μF

22pF

4x22μF

33pF

1.0μH

22μF

10pF

22pF

2x22μF

15pF

27pF

4x22μF

22pF

33pF

3.3V

0.47μH

&

0.68μH

158kΩ

34.8kΩ

22μF

22pF

-

2x22μF

33pF

-

4x22μF

47pF

-

1.0μH

22μF

22pF

-

2x22μF

33pF

-

4x22μF

47pF

-