TPS40054

TPS40055

TPS40057

SLUS593B − DECEMBER 2003 − REVISED APRIL 2004

8

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APPLICATION INFORMATION

The TPS40054/55/57 family of parts allows the user to optimize the PWM controller to the specific application.

The TPS40055 is the controller of choice for synchronous buck designs which will include most applications.

It has two quadrant operation and will source or sink output current. This provides the best transient response.

The TPS40054 operates in one quadrant and sources output current only, allowing for paralleling of converters

and ensures that one converter does not sink current from another converter. This controller also emulates a

standard buck converter at light loads where the inductor current goes discontinuous. At continuous output

inductor currents the controller operates as a synchronous buck converter to optimize efficiency.

The TPS40057 operates in one quadrant as a standard buck converter during start up. After the output has

reached the regulation point, the controller operates in two quadrant mode and is put in a synchronous buck

configuration. This is useful for applications that have the output voltage ’pre-biased’ at some voltage before

the controller is enabled. When the TPS40057 controller is enabled it does not sink current during start up which

would pull current from the pre-biased voltage supply.

SETTING THE SWITCHING FREQUENCY (PROGRAMMING THE CLOCK OSCILLATOR)

The TPS4005x has independent clock oscillator and ramp generator circuits. The clock oscillator serves as the

is charted in Figure 2.

R

1

f

SW

17.82

* 17 kW

(1)