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TRF7960: Receive problem

Guido Andrea Tedeschi
Prodigy 120 points
Part Number: TRF7960
Other Parts Discussed in Thread: MSP430F247,

My product uses TRF7960 with parallel intrefacing to a MSP430F247 and it worked fine with ISO15693 and ISO14443 tags until we made a new PCB revision that includes very little modifications near the MCU (few SMD0603 resistors added) but nothing on TRF7960 circuit, except adding two 0 ohm SMD0603 resistors to choose the MSP430 XTAL input where route the TRF7960 SYSCLK (on previous board the SYSCLK was connected directly with XT1IN).

The ISO15693 tags are still decoded, but at shorter distance, and the ISO14443 tags are not decoded anymore.

Comparing the RF signals with the previous working revision, they seem the same on antenna and on RXIN1 and 2, the noise on power supplies are the same and the digital signals seem correct...

What I found is that the two RSSI with are 0 when doing the TRF7960 startup test (Status register returns 0x40 indicating the oscillator stability but low RSSI, instead of a typical 0x53) and with REQA of ISO14443 I have a continuos Collision even without any Tags (IRQ register is 0x02)!

Any suggestion?

Some other tests to make?

Thanks and best regards

G

  • 0
    TI__Guru*** 135355 points
    Hello Guido,

    Does the issue occur across multiple boards, or just a single one?

    Can you share the schematic for the TRF7960?
  • 0 in reply to Ralph Jacobi
    Prodigy 120 points

    Hello Ralph and thanks for the quick answer.

    I found the problem: it was an issue on the new PCB, where there is an open trace on the pin 6 and 7 of TRF7960 shortest return to GND, so those pins where still connected to GND but not via the shortest path.

    This made the reception noisy and gave the problem, repairing the GND trace with a small solder drop solved the issue and it worked as good as the previous PCB revision, both with ISO15693 and ISO14443

    Thanks and best regards

    Guido