ST ST7538Q, Application Note, Page: 50 / 56

Troubleshooting AN2744
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8 Troubleshooting
In this section the most frequently asked questions are described.
1. PROBLEM : the ST7538Q reference design board doesn't work at all.
What to check :
a) Check that the AC mains supply cable is well connected to CN2.
b) Check if the green LED D2 is on.
c) Check voltage on the 10 V test point near the ST7538Q. The value must be 9 to 11
V.
2. PROBLEM : the ST7538Q reference design board is not responding.
What to check:
a) Check the VDC 5 V voltage output. Spurious voltage spikes can cause dips on the
VDC line. This could force a shutdown of the Tx circuitry if the VDC voltage goes
below 1.5 V. The solution is to force a power-off by mains disconnection.
b) Verify if MCLK selected frequency is present to check whether the ST7538Q is
working.
c) Verify the connection between the reference design board and the communication
board and between the communication board and the PC.
3. PROBLEM : the ST7538Q reference design board does not transmit.
What to check :
a) Check the voltage on ATOP1 and ATOP2 test points with the oscilloscope ground
probe connected to the AVSS signal ground. Programmed carrier frequency must
be present on both lines.
b) Check that programmed board channel (CH1/CH2) is matching the carrier
frequency selected through the control register panel of the reference design
software window.
c) Check that there is no short-circuit impedance on the mains at the selected
transmitting channel.
d) Check CL voltage. CL voltage fixes the current limiting threshold. It has to be lower
than 1.9 V, otherwise the IC is put in current limit mode.
If current limit mode is forced on the transceiver, check the value of R19 feedback resistor
and if there are any short circuits in the transmission path on the board.
4. PROBLEM : the ST7538Q reference design board transmits only for a short while.
What to check :
a) Check transmission time-out setting. It has to be disabled for continuous
transmission.
b) Check if continuous or single sequence transmission is selected in the Tx panel of
the reference design software window. Select continuous mode to be able to force
a lasting transmission.
c) Check if zero-crossing function is enabled. If yes, verify the ZCOUT
synchronization bit.
d) Check that there is no short-circuit impedance on the mains at the selected
transmitting channel.
5. PROBLEM : the ST7538Q reference design board does not receive.