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General description

The STNRGPFx2 are digital controllers designed specifically for interleaved CCM boost PFC topologies in high

power applications and embed the Inrush current limiter function.

The Interleaving technique splits the PFC management into two or more parallel channels depending on the load

condition. The driving signal will be out of phase of a proper value.

This phase shift will be calculated basing on the number of paralleled channels according to the following formula:

Equation 1

Pℎase sℎift= 360°

number of cℎannels

The benefits of the interleaved topology, compared to traditional single stage PFC, are measured in terms of

reduction of EMI filter and inductor volume, and a reduction of rms capacitor current.

The STNRGPFx2 contain all the control functions for designing a high efficiency-mode power supply with

sinusoidal line current consumption.

They work in CCM, fixed frequency with average current mode control, implementing a mixed signal (analog/

digital) control joining the advantages of very high-end digital solution without typical limits of analog ones.

In the mixed signal approach, the inner current loop is performed in hardware realizing an analog Proportional-

Integral (PI) compensator, and the outer voltage loop is performed by a digital PI controller with fast dynamic

response.

The STNRGPFx2 can be configured by a dedicated software tool (eDesignSuite) in order to be customized for a

specific application. So, the user has to open the software tool, enters the converter specs and runs the

configurator. The results will be: Schematic, BoM, and Binary code containing the parameters calculated by the

tool.

The binary code can be downloaded into the STNRGPFx2 through the programming software STSW-

STNRGPF01 (by means serial interface) having a customized device that can be used like analog device ready to

use in application.

1.1

Inrush current limiter function description

The STNRGPFx2 devices have the Inrush Current Limiter function embedded. As soon as power supplies are

connected to AC line, they are subject to short-duration, high amplitude, input current called “Inrush Current”. The

inrush current continues until the voltage across the internal capacitors reaches approximately the peak amplitude

of the input AC line. If uncontrolled, the inrush current can damage the components of the power supply. Several

solutions can be adopted to limit this current and STNRGPFx2 devices are able to manage two control methods.

1.1.1

Inrush current limiter function with resistive element (STNRGPF02 only)

One method to limit the Inrush Current is to add a resistive element R (resistors, thermistors, etc.) in series with

DC capacitors. Figure 1 shows one implementation of this technique. As soon as the capacitor C is charged, no

current flows, and the STNRGPF02 will do the ON signal to switch S1 in order to short R. In this way the losses

during normal operation are minimized.

STNRGPF02, STNRGPF12

General description

DS12895 - Rev 2

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