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TPS65982: TPS65982 Sink Current read from ADC

Hariprasad Bhat
Intellectual 630 points
Part Number: TPS65982

Hello,

We are using TPS65982 PD controller in our custom proto board and able to test Alternate Mode DP, USB Gen2 and PD Sink features.

In PD Sink feature, we are having 5# high current LEDs connected to PP_EXT rail. We can control these LEDs by controlling the FET gate pins as shown in attached snapshot.

Even we are able to control the LEDs (ON & OFF) as power our requirement.

Our requirement includes to measure the current getting sunk. We used Aardvark programmer (I2C) to access the PD controller registers. Even we are able to read the voltages @ VBUS, SENSEP, GPIOs etc. But, if I read I_PP_EXT (current through PP_EXT path), then always it will be 0A using TI Utility. If I measure using digital multi-meter then with 12V PP_EXT, the current consumption is ~90mA.

I have also attached the SENSE resistor schematics for your reference. I understand that current through PP_HV can not be read via ADC when it is sinking. But, datasheet says that I_PP_EXT can be read if 10mohm R(Sense) is used. [8.3.3.12 External HV Power Switch as a Sink with RSENSE]

We have used "RL0805FR-7W0R01L" as sense resistor.


Please suggest us how to proceed further to digitally read the current using internal ADC.

/cfs-file/__key/communityserver-discussions-components-files/138/8512.PP_5F00_EXT_5F00_SNK.zip

With Regards,

Hariprasad Bhat

  • 0
    TI__Mastermind 36756 points

    Hi Hariprasad,

    From looking at your circuit schematic, the SenseN and SenseP pins are swapped on the sense resistor for measuring the external sink current. Please refer to the image below to see the changes that need to be made:

    More details can be read in section 8.3.3.12 of the TPS65982 datasheet.

    Thank you,

    Eric

  • 0 in reply to Eric Beljaars
    Intellectual 630 points

    Hi Eric,

    Yes, I observed that too since we have followed EVM.

    I had the other option to swap the senseP and SenseN nets as in EVM. So, I removed R60 and R334, mounted R61 and R335. 

    Previously (without swapping Sensep and sensen nets) PD2_GATE1 and PD2_GATE2 were high (~14-18V), so VBUS was appearing at VBUS_SINK-C2 net (PP_EXT).

    But, with swapping the nets, I am seeing PD2_GATE2 is ~12V so, VBUS is reaching till drain pin of U68, but PD2_GATE1 is 0V. So, I am not able to get VBUS @PP_EXT net.

    I checked with BUSPOWERZ pulled to 1.8V and pulled down to ground with latest configuration. In both the cases, PP_EXT will not get VBUS.

    I am attaching the .pjt file which was used to generate the firmware. 

    /cfs-file/__key/communityserver-discussions-components-files/138/8623.4035.SEDIM_5F00_CARD_5F00_SNK_5F00_EXT_5F00_PATH.pjt

    With Regards,

    Hariprasad Bhat

  • 0 in reply to Hariprasad Bhat
    TI__Mastermind 36756 points
    Hi Hariprasad,

    The orientation of the Sense resistor with regards to SENSEP and SENSEN should not change the voltage of PD2_GATE1 or PD2_GATE2.
    Are you booting the device in dead battery mode? If so, BUSPOWERZ should be set to 1.8V.

    Thank you,
    Eric
  • 0 in reply to Eric Beljaars
    Intellectual 630 points

    Hi Eric,

    I am not booting in dead battery mode and I understand the BUSPOWERZ functionality. It was just an attempt to get something out of it.

    I agree regarding the SENSEP/N orientation GATE Enable from PD.

    So, I just completed the swapping in one more board and with that I am getting both the GATE enables from PD. But, still the current read is 0A.

    One more thing, the current sunk by our card with 12V is under 100mA. 

    I see in the datasheet under 6.11 Port Power Switch Characteristics : 

    IHVEXT_ACC characteristics : I = 100 mA , RSENSE = 10 mΩ Reverse current blocking disabled

    Does above statement imply that ADC can not measure the current below 100mA?

    I have tried one more things with the board where both gate enables are proper.

    I sourced 20V with the help of EVM as source (CFG ID# 6 ). I read the sourcing current in EVM and got the reading of  ~117mA. But, with sink (custom board) it is still the same 0A.

    With Regards,

    Hariprasad Bhat