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TPSM84424: Big idle current

Igor Trudonoshin
Prodigy 30 points
Part Number: TPSM84424

Hello.

I build a prototype with TPSM84424 as 14V to 5V converter and found,

that idle current of part is about 50 mA in on-load conditions.

Part is hot, about 55 celsius at idle, wasting about 700 mW of power.

Part is working normally at 1-2-3-4 A load.

Is this idle consumption connect ?

It seems to me that it's to much current for idle....

Any ideas to check ?  This is repeated on 4 parts, so it should not be a single failure related...

  • 0
    TI__Guru 50120 points

    Hi Igor,

    Can you please provide the schematic and PCB layout for me to review. You can contact and send me the files directly at j-hua@ti.com 

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    TI__Guru 50120 points

    Hi Igor,

    Regarding the idle current under no load, it might be a bit  high but not alarming to see roughly ~50mA idle current for 5Vout in our EVM. Also under no load  condition the temperature is expected to be around 40°C.

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    Prodigy 30 points

    Hi. 
    File attached.

    If I understand correctly, 50 mA is the same on Eval borad...so, there is nothing to do with my issue.

    TI_TPSM84424.ZIP

  • 0 in reply to Igor Trudonoshin
    TI__Guru 50120 points

    Hi Igor,

    I'd like to ask for some clarification on the issue.

    When you say idle, do you mean that the part is powered up and regulated with no load. If you are wondering if the wasted power is correct, I can only test on the EVM at no load to get a comparison. Under this idle condition the TPSM84424 is expected to see around 50mA current drawn from the power supply. However, 55C idle is rather high so I'd like on another EVM to test for idle current continuity between 2 EVMs.  

    Also let me take a look at the PCB layout and get back to you on this. 

    Regards.

    Jimmy 

  • 0 in reply to Jimmy Hua
    TI__Guru 50120 points

    Hi Igor,

    I've tested another EVM in the lab and the result at idle (14Vin-> 5Vout at no load and room temperature), the input current drawn from the power supply is ~49-50mA. However this does not get hot to 55C that you see. I want to reconfirm that this is the condition you applied to your system at "idle". 

    Are you measuring the top of the exposed inductor when you got the 55C reading? Also can you give me an update of your schematic. The schematic you've sent looks like it is using placeholder component values. The BOM used on the EVM that I tested with is shown in the EVM User Guide. I'd like to make sure that you are using the recommended 1.2MHz switching frequency with 18kOhm of Rtt turbo trans setting detailed in Table 1. 

    Looking at your PCB layout, bottom layer and Layer S2 are ground which should provide thermal relief to the part.

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    Prodigy 30 points

    HI.

    Real values of components are in TXT file in archive.

    55 is inside  module, under the inductor, measured by small isolated thermocouple. It could be not really accurate, but close to true.

    OK, I have the same result - 50 ma in same conditions ( load is only a feedback divider ), all 50ma*14V = 0.7W is dissipated to heat,

    so it is the same.

    Thanks.