Figure 5. Voltage loop and current reference

The output of digital PI is the peak current reference. In order to obtain a sinusoidal current reference Ipk_ref is

multiplied by a Look-Up Table (LUT). The LUT is synchronized with the Input voltage thanks to the ZVD signal

(pin 17). The output of multiplier is a PWM signal having sinusoidal Duty Cycle that is configured on Pin 4 SIN

REF.

An Analog filter is used to obtain the final sinusoidal current reference for the external current loop (Itot_ref). The

analog current PI compare the reference Itot_ref with the total input current feedback (Itot_fb) and generate the

duty cycle wave for PWM modulation. The master PWM signal is obtained by comparing (COMP2,3) the output of

current PI (pin 24, pin 25) with a triangular wave (pin 26) at switching frequency (see Section 3.3 Analog

comparators section and Section 3.4 PWM Section: driving & interleaving).

3.2

Measurements section

The STNRGPFx2 include 4 input measurements channels. These inputs are defined from Pin 31 to Pin 38 and

they are below specified.

•

Pin 31. Vin_L1: AC Input Voltage measurement Line 1

•

Pin 32. Temp: ambient temperature.

•

Pin 33. Iout: PFC output current.

•

Pin 34. Vout: PFC output voltage.

•

Pin 35. I[0]: RMS current channel [0]

•

Pin 36. I[1]: RMS current channel [1]

•

Pin 38 AVin_L2: AC Input Voltage measurement Line 2

3.2.1

AC input voltage measurement

The STNRGPFx2 have two dedicated pin’s, Pin 31 and Pin 38, for AC RMS line voltage measurement. The

devices, by means two resistor dividers, measures simultaneously the instantaneous voltage on both pins,

performs the difference between them and calculate the rms value (see Figure 1 Vin_fb signal). Vin_fb (RMS AC

input voltage) is used for the following functions:

a) Normal operation. It’s used to generate the sinusoidal current reference signal.

b) AC input voltage variation. This signal is used to implements the Input Voltage Feed Forward that

modifies the vo ltage PI output compensating rapidly the effect of the line voltage changes. See Figure 6

STNRGPF02, STNRGPF12

Measurements section

DS12895 - Rev 2

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