TS3552

2A/350kHz Synchronous Buck DC/DC Converter

6/11

Version: B11

Application Information (Continue)

Optional Schottky Diode

A Schottky diode with low forward drop voltage and fast reverse recovery is the ideal choice for better efficiency.

The forward drop voltage of a Schottky diode will result in the conduction losses in the diode, and the diode

drop and diode capacitance for diode selection. In addition, the rating of selected Schottky diode should be able to

handle the input voltage and the maximum peak diode current.

Input Capacitor the Output Capacitor

To prevent the high input voltage ripple and noise resulted from high frequency switching, the use of low ESR

ceramic capacitor for the maximum RMS current is recommended. The approximated RMS current of the input

capacitor can be calculated according to the following formula.

The selection of output capacitor depends on the required output voltage ripple. The output voltage ripple can be

expressed as:

For lower output voltage ripple, the use of low ESR ceramic capacitor is recommended. The tantalum capacitor can

also be used well, but its ERS is larger than that of ceramic capacitor.

When choosing the input and output ceramic capacitors, X5R and X7R types are recommended because they

retain their capacitance over wider ranges of voltage and temperature than other types.

Loop Compensation

In order to avoid the poor output voltage ripple and low efficiency caused by instability, TS3552 requires a proper

external compensation network to compensate its feedback loop. In this external compensation network, the

compensation resistor, RC, and the compensation capacitor, CC, are used to set the high-frequency integrator gain

and the integrator zero. C7 is used to cancel the zero caused by the output capacitor and it’s ESR. While using the

ceramic capacitor as the output capacitor, C7 can be omitted due to the small ESR.

The system has one pole of importance, due to the output capacitor, C3//C4 and the load resistor. This poles is

located at: