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  • TI Thinks Resolved

TPS40422: PMBus READ_OUT dependency on PAGE register in case of two-phase single out put mode

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Replies: 11

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Part Number: TPS40422

Hi,

I am using TPS40422 device in two-phase single 3.3V output mode and we are trying to read current values at READ_IOUT register 8Ch for total current consumed on this power rail. 

Do we need to add the measured current at 8CH by selecting channel 1 and channel 2 using the PAGE register 00h for a total current?

or  Since the device operates two-phase mode it is not required to add channel 1 and channel 2 current?

PAGE select register value does not matter for READ_OUT in the case to two-phase mode? 

Thanks

Sivaguru

  • HI Sivaguru, 

    READ_IOUT register report phase current, not total current. 

    You need to use PAGE register to select channel, read phase current from READ_IOUT register, then add phase current together for total load current. 

    Thanks

    Qian

  • In reply to Qian Chen:

    Thanks Qian for the details on READ_IOUT.

    One more question, how the margin command should be issued using the OPERATION (01h) register ? because this also is a paged register.

    Do we need to select page 0 and issue margin high command and then select page 1 and issue a margin high command?

    Thanks

    Sivaguru  

  • In reply to Sivaguru Thanikachalam:

    Hi Sivaguru, 

    In 2phase configuration, ch1 control loop is used to regulate Vout. ch2 control loop is not in use. 

    Therefore ch1 (page 0) should be selected first and then use margin command to adjust Vout. 

    Thanks

    Qian

  • In reply to Qian Chen:

    Thanks Qian,

    Also, please explain how does the following paged register will work in the case of two-Phase singe output voltage mode? 

    IOUT_OC_WARN_LIMIT (4Ah)

    IOUT_OC_FAULT_LIMIT (46h)

    IOUT_OC_FAULT_RESPONSE (47h)

    Thanks

    Sivaguru

  • In reply to Sivaguru Thanikachalam:

    HI Sivaguru, 

    All three registers refers to phase current in 2phase configuration. 

    Thanks

    Qian

  • In reply to Qian Chen:

    Hi Qian,

    I did an experiment in the lab to understand about READ_IOUT (8Ch) in a two-phase single output configuration. 

    1. Loaded 3.3V power rail with external electronic load

    2. Increased the load current to 20A 

    3. Read PAHSE 1 and PAHSE 2 current by writing appropriate values into the PAGE register. Refer below register read values during the experiment. 

    Page 0, READ_IOUT (17.5A)

    [diag@TOR1 ~]# pcimemread 0xc80002A4 4
    PCI memory 0xc80002a4 align memory 0xc8000000 (mmap addr 0x7f7aa6852000(0x2000))
    c80002a4 : 0000e118

    Page 1, READ_IOUT (16.3125A)

    [diag@TOR1 ~]# pcimemread 0xc80002A4 4
    PCI memory 0xc80002a4 align memory 0xc8000000 (mmap addr 0x7f77893de000(0x2000))
    c80002a4 : 0000e105

    4. If we add total current would be 33.8125A which is not possible as per the lab setup which i had. 

    5. So for me, it looks like PHASE 1 OR PAHSE 2 current itself is a toal current.  No need to add both PAHSE current to arrive total current. 

    6. If so there is a ~2.5A meaurement error observed with this device TPS40422 which is exceeding the datasheet limits. Can you check ? 

    Can you please re-confirm the READ_IOUT behavior in two-PAHSE singe output configuration?  Also, confirm all other relevant registers we discussed previously. 

    IOUT_CAL_GAIN

    IOUT_CAL_OFFSET

    IOUT_OC_FAULT_LIMIT

    IOUT_OC_FAULT_RESPONSE

    IOUT_OC_WARN_LIMIT

    Thanks

    Sivaguru

  • In reply to Sivaguru Thanikachalam:

    Hi Sivaguru, 

    What's the inductor DCR (or equivalent DCR)  and IOUT_CAL_GAIN value?

    IOUT_CAL_GAIN should be equal to DCR value. 

    Thanks

    Qian

  • In reply to Qian Chen:

    Hi Qian,

    Refer below IOUT_CAL_GAIN value (38h) values read from the board. Its a defualt vlaue. 

    [host:0_RP0:~]$ pcimemread 0xc80002A4 4
    PCI memory 0xc80002a4 align memory 0xc8000000 (mmap addr 0x7fefbbfaa000(0x2000))
    c80002a4 : 00008810 ....

    On the inductor, DCR, refer attached datasheet for your reference.

    DCR - 0.96 to 1.06 ohms (Typ to Max )  for PAHSE 1 and PAHSE 2. 08_15_2013_avl11409359.pdf

    Thanks

    Sivaguru

  • In reply to Sivaguru Thanikachalam:

    Hi Sivaguru, 

    If IOUT_CAL_GAIN does not match DCR value, the current readout and OC trip point will be wrong. 

    Can you change IOUT_CAL_GAIN to typical DCR value and check again?

    Thanks

    Qian

  • In reply to Qian Chen:

    Hi Qian,

    Updated IOUT_CAL_GAIN value with proper inductor typical DCR value but still i could see some inaccuracy in current reading. 

    I have written the following value 0x8820 into IOUT_CAL_GAIN value which translates to 0.976mOHM on both PHASE 0 and 1. 

    pcimemwrite 0xc80002A4 4 0x8820

    I have made 20A electronic load in the lab setup and but I could read-only (8.8+8.1=16.9A) thro READ_OUT register.  Can you suggest why this inaccuracy? 

    PAGE-0

    [diag@TOR1 ~]# pcimemwrite 0xc8000244 4 0x823f8c00
    Write at Address 0xc8000244 (mmap addr 0x7f68a8c5b000(0x244)) value 0x823f8c00 len 4 width 4 byte
    [diag@TOR1 ~]# pcimemread 0xc80002A4 4
    PCI memory 0xc80002a4 align memory 0xc8000000 (mmap addr 0x7f26a991f000(0x2000))
    c80002a4 : 0000e08d

    8.8125A

    PAGE-1

    [diag@TOR1 ~]# pcimemwrite 0xc8000244 4 0x823f8c00
    Write at Address 0xc8000244 (mmap addr 0x7f2d6cfd5000(0x244)) value 0x823f8c00 len 4 width 4 byte
    [diag@TOR1 ~]# pcimemread 0xc80002A4 4
    PCI memory 0xc80002a4 align memory 0xc8000000 (mmap addr 0x7fda09394000(0x2000))
    c80002a4 : 0000e083

    8.1875A

    Thanks

    Sivaguru

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