AN1714 datasheet(21/46 Pages) STMICROELECTRONICS

21 / 46 page

AN1714

Demonstration board for ST7538Q

21/46

2.2.3

Voltage regulation-current protection loops

A powerline network requires an appropriate driving circuit able to adapt the output signal

characteristic to the different and low values of the mains impedance.

Figure 18.

Powerline output characteristics

Figure 18 shows the characteristic of a coupling circuit. The characteristic has a range with

constant voltage amplitude of the transmitted signal. When the line impedance has reached

a critical Z0 value, corresponding to the maximum power, the amplitude of the output signal

is decreased in order to have a constant current.

The value of Z0 depends mainly on the network impedance, while the maximum value of V0

depends on the norm (EN50065-1) and on the maximum current capability of the powerline

interface.

The ST7538Q integrates a control voltage / current protection circuit. It is possible to

program the values of Z0 and V0 with external resistors. The R13 trimmer sets the current

protection limit and the R14 and R12 trimmers the peak voltage level. The dimension of

these external components influences the design of the coupling interfaces and of the power

management, too. For example all the components in series to the signal (transformer, filter

inductors, decoupling capacitors, fuses) have to guarantee a maximum current or a

saturation current greater than the maximum current programmed with R13, as well as the

dimension of the current capability of the power supply. The capacitors on the supply line

have to be chosen according to the programmed current values.

The control loop circuit inside the devices is obtained by a Voltage Controlled Amplifier

(VCA) with a logic circuit that implements the following control (Figure 20). The current

protection has the priority with respect to the voltage loop regulation, so if an output current

greater than the programmed value (Iref > IH) is detected, the digital control acts on the VCA

to reduce the output signal voltage. When the current reaches the programmed value, the

gain of the VCA is frozen.

In case of no current protection condition (Iref < IL), the voltage regulation loop assumes the

control and modifies the gain of the VCA until the output signal reaches the programmed

values.

The VCA changes its gain at steps of about 1dB (10%). The logic samples the current and

voltages values with an internal clock of 5 Hz, so the transmitted signal is updated every 200

µsec at steps of 1 dB.

I zone

V zone

Line load (ohm)

Signal

Amplitude

I zone

V zone

Line load (ohm)

Signal

Amplitude

AN1714 датащи(PDF) 21 Page - STMicroelectronics

AN1714 датащи(HTML) 21 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

датащи скачать

ссылки URL