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Trf7970a's transmit power

user3305641
Prodigy 100 points
Other Parts Discussed in Thread: TRF7970A, RF430FRL152H

Hello,

I am Eric,from China.Recently,I have a problem about Trf7970a's transmit power.In datatsheet，when at 5V, B4 of Chip Status Control Register is 1,the  transmit power is 200mW.

But when I finished these settings，the NFC communication distance is only 1.5cm,Far below expectations！The following figure is my test planform:

The ISO15693 protocol is used, and the receiver chip is RF430FRL152H on the tag.In figure, 

Trf7970a(pin2)的Vin is set as 4.8V,Chip Status Control Register as 0x03:
TRF79xxA_writeRegister(TRF79XXA_CHIP_STATUS_CONTROL, 0x03);//5V operation
But when I read Chip Status Control Register:
TRF79xxA_readRegister(TRF79XXA_CHIP_STATUS_CONTROL)
it returns 0x20.My questions is:
1.Why it returns 0x20?
2.How can set Trf7970a power as 200mW(max),and How to make sure the power?

  • 0
    TI__Guru*** 128255 points

    Hello Hao,

    The Chip Status register returned 0x20 likely as the firmware should be automatically setting the Chip Status Control at each attempt to read a tag.

    If it's returning 0x20 and not 0x21, that tells me you haven't told the firmware stack that you are running at 5V. This is done at initialization time with the API:

    TRF79xxA_setTrfPowerSetting(TRF79xxA_5V_FULL_POWER);

    Since you have a mismatch of supplied voltage vs what the TRF7970A is trying to drive, you are getting poor range. Please make sure the firmware has been properly configured for 5V operation at initialization and try to measure read range again.