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TPSM365R6FEVM: Excessive current during initial powering up

Richard Payne
Prodigy 30 points
Part Number: TPSM365R6FEVM

Tool/software:

I have received TPSM365R6FEVM from Digikey and identify the current consumption from Bench PSU read 14mA from 24V which is deemed excessive compare to datasheet which quoted less than 10uA unloaded current even in FPRM mode. When EN jumper to OFF, it drop to 0mA. When EN jumper to ON, it read 14-15mA. No RLOAD is connected. It seem to be functional with RLOAD test.  

Nothing in the TPSM365R6FEVM document mentioned expected current.  

  • 0
    Prodigy 30 points

    In addition, I have tried 400KHz to 2MHz and it has same VIN current readout.

  • 0 in reply to Richard Payne
    TI__Mastermind 29145 points

    Hi Richard,

    The datasheet quoting the 10uA unloaded current refers to when the device is connected to the Bias pin (i.e. fixed output). I think what you are currently seeing is the current being consumed by the resistor divider, RT pin, and VCC. 

    The suggestion here is to use fixed output 3.3V device, connect output directly to FB pin. I think the current will be reduced. 

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Prodigy 30 points

    Looking into EVAL schematic where jumper is placed on 12V / (~120K total) which is only 100uA in feedback. That does not factor 14mA I'm seeing now. Digikey has shipped replacement unit. I also note I unable to change frequency via jumper.  

  • +1 in reply to Richard Payne
    TI__Mastermind 29145 points

    Hi,

    Just wanted to account for a few possible reasons to see the increased current. I believe this case matches something similar that I've seen with other devices in FPWM when output isn't used to power the internal regulator. 

    It is strange that the frequency is not changing. Let me know how replacing the unit goes. 

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Prodigy 30 points

    I have 2nd EVAL and then connected to 24V Bench PSU, set to 1MHz and 12V O/P setting. I still get 14-15mA from 24V Bench PSU. I check with Fluke 179 for 24V current readout and found same reading as Bench PSU. Would it be possible to you check your end and identify why this is higher current than datasheet?

  • 0 in reply to Richard Payne
    Prodigy 30 points

    Based on chart Figure 8-9 and 8-10, with 1mA RLOAD, I get this. I think the datasheet is just avoiding simple parameter under DC load condition base on two operating mode. 

    For AUTO mode with 60% efficiency:

    • POUT = 12V × 1mA = 12mW
    • Efficiency = POUT/PIN = 0.6
    • So PIN = POUT/0.6 = 12mW/0.6 = 20mW
    • Therefore IIN = PIN/VIN = 20mW/24V = 0.833mA

    For FPWM mode with 4% efficiency:

    • POUT = 12V × 1mA = 12mW
    • Efficiency = POUT/PIN = 0.04
    • So PIN = POUT/0.04 = 12mW/0.04 = 300mW
    • Therefore IIN = PIN/VIN = 300mW/24V = 12.5mA
  • 0 in reply to Richard Payne
    TI__Mastermind 29145 points

    Hi,

    I can check, but I think it makes sense that the FPWM device would have a higher current consumption. The TPSM365R6FEVM utilizes the FPWM trim, so I think it matches the expected value that you are seeing. I have ordered a board and it should be coming in this week.

    Thanks

    Richard 

  • 0 in reply to Richard Fu22
    Prodigy 30 points

    It a pity there no EVAL board using AUTO-MODE, thing would be different.

  • 0 in reply to Richard Fu22
    Prodigy 30 points

    In addition in section 8.6, the Supply Voltage (VIN) table with two different voltage setting imply 6.5uA and 4uA, not very clear what this number really is but found it very misleading. It seem to imply quiescence current without load current. 

  • 0 in reply to Richard Payne
    TI__Mastermind 29145 points

    Hi,

    We do have a EVAL board using the AUTO feature, it is the TPSM365R6EVM. I think, in order for you to save cost, it is better to get TPSM365R6RDNR samples and place it on the EVM that you have. 

    And section 8.6 are some values noted from the closed-loop validation of the part. It is not a guarantee, as noted:

    In any case, let me check and confirm the measurement with you as previously discussed. 

    Thanks,

    Richard