TRF7970A: The RFID module read card seems not working under 70 degree

Any update?? Thanks,

Hello Aichi,

OSC_OUT belongs to the crystal oscillator. Have you verified that the used crystal is meeting the temperature ratings?

Was the crystal's load cap matching to the crystal type?

How many ICs of TRF7970A are affected?

If it is just one IC, then I would suggest to return the IC through our supplier.

Best regards,

Andreas.

Hi Andreas,

Q: OSC_OUT belongs to the crystal oscillator. Have you verified that the used crystal is meeting the temperature ratings?

--> The crystal is using -40 ~ 85 degree temp. following by TI suggestion.

Use Function generator and TCXO  to replace Crystal get same issue.

Q Was the crystal's load cap matching to the crystal type?

->Yes

3.How many ICs of TRF7970A are affected?

-> Its around 60% of 4800 pcs.

BTW, my customer report that if we were reading card via polling mode, the fail unit will be pass the testing. But it will fail if we just send command/response via UART(from host to MSP side).

After the unit fail, we just need to reboot RFID module, it will be recoverable.

Hope we could have work around to fix it under non-polling mode.

Hello Aichi,

currently I'm communicating to the customer support, which you also contacted.

I will not update here in parallel, but I will post the conclusion here when available, in order to share the solution to the forum members.

Best regards,

Andreas.

Hi, 

we are quite urgent on this issue as this block MP schdeule and may lost business. Any update??

The customer has done more testing:

1.As you suggested, I am testing with the following conditions.I will share the results with you after the test is completed.

   #1.MSP430 would be powered by the VDD_X(TRF7970A)

       //TRF7970 Vin=3.3V

   #2.MSP430 would be powered by the VDD_X(TRF7970A)

      //TRF7970A Vin=5V

2.https://www.ti.com/lit/pdf/sloa205

   In this manual, all the explanations are about the IO configuration of Power-Down Mode.

   For our application, the module will not enter Power-Down Mode.

   I connect EN2 to gnd, EN pull down and connect to msp430 I/O.
   Is this configuration ok?(Reference document page.26)   

   https://www.ti.com/lit/an/sloa184/sloa184.pdf?ts=1654588279068&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTRF7970A

3.Test the bad board, change C12 to 330pF, 70% of which can work properly at high temperatures.

   We measured the changed RX voltage to be about 2V, compared to about 2.7V.

   Is it possible that this is one of the reasons?

Hello Aichi,

Here are my answers:

1. OK. Alternatively it would be OK to connect VDD_I/O to VDD of the MSP430.
2. This configuration still can cause Power Down Mode, if the MSP430 I/O is forcing low. In this state also VDD_X turns off, which means the MSP430 can not be powered from VDD_X. Please refer to table 6-3 in the TRF7970A Data Sheet. If the MSP430 is supposed to control the Power Down Mode, then it must be powered form a permanent voltage, other than VDD_X (for example VDD, and VDD_I/O also connected to VDD.
3. C11=C12=1200pF is the reference design. To be honest, I never have seen applications, not using the reference design for antenna matching. (I also have not seen before temperature dependency in the matching circuitry.) Lowering C12 should lower the voltage at RX_IN1 on a first glance, but I’m not sure how it de-tunes the whole matching. You may refer to chapter 6.4.1 in the TRF7970A Data Sheet for more details on the RX inputs, but at the end I would recommend to stick to the reference design. On the other hand if the modified circuitry is working better then it would be probably a valid approach. Maybe the layout is sub-optimum an de-tuning the matching and maybe the modified C12 is compensating this mismatch. I don’t know. Actually you could measure the TX output power at CON-P1 to confirm matching.

Let me know if you have further questions.

Best regards,

Andreas.

Hi,

For Q1,Q2

We tested by below steps but no luck. 

1.TRF7979A VDD_IO connect 3.3V

2.MSP430 VDD connect to TRF7970A VDD_X

3.MSP430 VDD connect to 3.3V

4.TRF7970A VDD connect to 5V

Only turn low TRF7970A RX_IN1, can lower the fail rate..

For Q3,

We try to maximize TX power.

But since the problem will only happen faster, we still adjust the c12 capacitor to reduce the RX voltage to reduce the problem.

One more question, is that possible TRF7970A change something in factory?

Actually we use same design almost 8~9 years no such issue without any HW/SW change. But in recently we just met this issue around 60% of 2.5K units.

This is our labels.

Hello Aichi,

thanks for your feedback.

I checked TRF7970A manufacturing and there hasn't been any abnormality.

Please send back some of the bad devices through the customer return channels of your distributor.

Best regards,

Andreas.