AN3290

Test board design and evaluation

Doc ID 18038 Rev 1

5/34

1

Test board design and evaluation

As a reference design, a 7.48 W nameplate output power SMPS has been specifically

designed and developed according to the specifications for a complete power line

communication based on ST7580 (by STMicroelectronics).

The power supply provides a 13 V output voltage to supply the power line modem (PLM)

and the analog circuitry, and a post-regulated 3.3 V to supply digital circuitry and an optional

external microcontroller.

Table 1 summarizes the electrical specifications of the power supply, Table 2 provides the

bill of material and Table 3 lists the transformer specifications. The electrical schematic is

shown in Figure 2 and the PCB layout in Figure 3 and 4.

The input stage, consists of an NTC (NTC1) which limits the inrush current produced by the

capacitor charging at plug-in and a varistor (RV1) that protects the power supply against

temporary line overvoltage transients. The input EMI filter is a classic Pi-filter, 1-cell for

common and differential mode noise. The clamping network (D2-D3) limits the peak of the

leakage inductance voltage spike at turn-off, assuring reliable operation of the ALTAIR04-

900.

The sense resistor R2 and the transformer primary-to-secondary turn ratio fix the maximum

output current limitation, whereas the voltage divider made up of R6, R7, and R8 is used to

set the output voltage setpoint, in order to ensure the desired output voltage regulation. The

network connected on the COMP pin is used to compensate the loop, ensuring the right

gain and phase margin to the system, whereas the voltage across the capacitor C10 is used

to fix the voltage level for the CC loop; the value of this capacitor is not critical and e few nF

are enough to ensure correct operation. The secondary side is provided by two output

voltages; a nameplate 13 V output voltage is directly used to supply the analog circuitry of

the PLM, whereas the lower voltage is achieved by a 3V3 LDO and is intended to supply the

digital parts.

Table 1.

ALTAIR04-900 power supply: electrical specification

Parameter

Note

Min.

Typ.

Max.

Unit

AC main input voltage

85

265

50

60

Hz

Output voltage 1

Analog supply voltage

11.7

13

14.3

V

Output current 1

Rx mode

12

mA

Tx mode

35

550

mA

Output voltage 2

Digital supply voltage

3.3

V

Output current 2

No external microcontroller connection

40

50

mA

External microcontroller connection

100

mA

Total rated output power

7.48

W

Maximum output power

In TX mode

4.2

W