PN7150 TXLDO Config with PMU_CFG

[gwctree42]

Hi I have an nfc system based on PN7150. I had some trouble configuring the TXLDO and I think there might be a bug in the documentation on PMU_CFG byte2. I'm referring to UM10936 PMU_CFG definition on p88. 

I have my system configured as power config 2 with VDD(PAD)=3.3 and VBAT=VBAT1=VBAT2=5 (both 3.3V and 5V are regulated).

I attempted PMU_CFG = 0x6 0x64 0x1 and measured that TXLDO voltage only goes up to 3.0V 

But when I tried PMU_CFG = 0x6 0x64 0x0, TXLDO went to 4.7V 

The register definition says PMU_CFG byte2 should =0x1 for CFG2 

My three questions: 

1. Could you explain what PMU_CFG byte2 does, and if it is accurate that it should be 1 for CFG2, and why did it make TXLDO go to 4.7V when I set byte2=0 ?

2. Could you confirm what the setting for PMU_CFG is supposed to be for the highest possible power with config 2, VBAT=5 ? 

3. Are there any scope shots available showing how VDD(TX) is supposed to look like ? I'm seeing 0.6Vpp ripple at 13.5MHz and I'm wondering if that is expected or if my system needs more bulk caps.

(I know PN7150 is nrnd and you recommend PN7160 instead. I am doing sustaining work on an old product.) 

[Tomas_Parizek]

Hello gwctree42, 

The voltage ripple at the beginning is typically due to the 100% modulation of NFC-A technology. This is quite normal. 

About the difference between my and your measurement, what is the version of your IC ? PN71501 or PN71506

BR

Tomas 

[gwctree42]

PN7150B0HN/C11002Y

[Tomas_Parizek]

Hello gwctree42, 

I tried to reproduce it with PN7150 dev. board with the following results: 

CFG2 -> 0x06, 0x64, 0x00

VDD(TX) without a card in the proximity 

VDD(TX) with the card in the proximity 

CFG2 -> 0x06, 0x64, 0x01

VDD(TX) without a card 

VDD(TX) with the card 

About the waveform, it might be that you coupled some RF signal during your measurement. Can you share some scope measurements ?

About the meaning of byte2, this I need to check internally. These statements/recommendations are typically coming from RnD team. 

BR

Tomas 

[gwctree42]

This is 0x6 0x64 0x0 with no card present. The 2nd pic is just zoom in just after the rising edge of VDD(TX). 

Looks like it behaves as expected with byte2=1 for you. Not sure what is different for me. Would be good to know if there is any downside to leaving byte2=0. 

Thanks for checking !