AN2451 datasheet(49/55 Pages) STMICROELECTRONICS

49 / 55 page

AN2451

Troubleshooting

Doc ID 12791 Rev 3

49/55

Troubleshooting

In this section the most frequently asked questions are described.

Problem: the ST7540 reference design board does not work at all.

What to check:

Check that the AC mains supply cable is well connected to CN1.

Check if the green LED D6 is on.

Check the voltage on the Vcc test pad. The value must be about 12 V.

Problem: the ST7540 reference design board is not responding.

What to check:

Check the VDC voltage. The value must be about 5 V. In a noisy environment,

spurious voltage spikes could compromise the internal linear regulator startup.

If Vdd is not externally connected to the VDC line, verify the Vdd voltage. The

value must be about 3.3 V.

Check if the MCLK selected frequency is present.

Check the connection between the reference design board and the

EVALCOMMBOARD and the connection between the EVALCOMMBOARD and

the PC.

Problem: the ST7540 reference design board does not transmit.

What to check:

Check the voltage on the PA_OUT test pad with the oscilloscope ground probe

connected to the SVss signal ground. The programmed carrier frequency must be

present on the PA_OUT line.

Check there is no short-circuit impedance on the mains at the transmitting

frequency.

Check the CL voltage. It fixes the current limiting threshold. It has to be lower than

1.9 V, otherwise the IC is put in current-limit mode.

If the current-limit mode is forced on the transceiver, modify the value of the R6 feedback

resistor to exit from limitation according to the actual load forced by the mains network.

Problem: the ST7540 reference design board transmits only for a short time.

What to check:

Check the transmission timeout setting. It has to be disabled for continuous

transmission.

Check if continuous or single sequence transmission is selected in the Tx panel of

the ST7540 powerline modem demonstration kit window. Select continuous mode

to be able to force a lasting transmission.

Check there is no short-circuit impedance on the mains at the selected

transmitting channel.

Problem: the ST7540 reference design board does not receive.

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