TPS54239: IC has 8mA of unexplained current draw

Alexander Farley

Prodigy 70 points

Part Number: TPS54239

Hi,

We're using a TPS54239 to generate 3.3V from an 8V source. Measuring each pin, I get the following:

EN: 8V

VFB: 0.75V

VOUT: 3.3V

VIN: 8V

VREG: 5.5V

SS: 5.5V

There is no load since I've disconnected the VOUT from this circuit to the load. In total, I see 8mA coming from VIN to drive this circuit. According to my reading of the datasheet, this part should draw maybe 1mA without any load, but nowhere near 8mA. VREG is also unloaded; I've confirmed by measuring to GND, which reads 0.5 megaohms. Measuring from VOUT to GND reads 40K.

Is this part expected to draw ~8mA when the output is not loaded?

over 5 years ago

0 Shawn Nie over 5 years ago

TI__Genius 10070 points

Hi,

1mA is the non-switching supply current of IC, but when you test the input current, the device operate normally, there is dissipation on the Rdson, DCR, and resistance of PCB.

Shawn

0 Alexander Farley over 5 years ago in reply to Shawn Nie

Prodigy 70 points

Hi Shawn, thanks for the details. Just to be clear, are you confirming that 8mA is actually expected in this scenario? I don't really see what the on-resistance or PCB trace resistance has to do with this. It seems to me that there's some internal 8mA current draw in the IC itself.

What is DCR? I don't see that term anywhere in the datasheet.

Thanks,

Alex

0 Shawn Nie over 5 years ago in reply to Alexander Farley

TI__Genius 10070 points

Hi Alex,

DCR is DC resistance of inductor, how did you measure the input current? And why do you concern about this data?

Shawn

0 Alexander Farley over 5 years ago in reply to Shawn Nie

Prodigy 70 points

I measured the input current by placing a multimeter in series with the power-supply input, with nothing else on the circuit except for this IC.

I'm wondering about the current usage because I'm working on a design that's highly sensitive to excess current draw, and 8mA of current draw when no other load is present is far too much for our application.

0 Shawn Nie over 5 years ago in reply to Alexander Farley

TI__Genius 10070 points

Hi,

I think it is reasonable, you can calculate the input current roughly to double check it.

Shawn

0 Shawn Nie over 5 years ago in reply to Shawn Nie

TI__Genius 10070 points

Hi,

Which part dose you use? TPS54239 or TPS54239E? TPS54239 is FCCM, and TPS54239E is Eco-mode at light load.

If you want to save the loss, you'd better to use TPS54239E.

Shawn

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TPS54239: IC has 8mA of unexplained current draw