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TPS63070: Datasheet clarification of "into Vin" and "into Vout" for quiescent current, quiescent minimisation

Robert Brown66
Prodigy 100 points
Part Number: TPS63070
Other Parts Discussed in Thread: TPS63020

Hi All,

I'm designing a buck/boost and the TPS63070 looks like it will meet the spec. I have to carefully budget the system quiescent current, as it is a very tough to meet low power specification. Quoting from the datasheet -

IQ Quiescent current into VIN; IOUT= 0 mA,
VEN = VIN = 6 V, PFM
VOUT = 5 V; Tj = -40°C to 85°C		 54 103 μA
IQ Quiescent current into VIN; IOUT= 0 mA,
VEN = VIN = 6 V, PFM
VOUT = 5 V; Tj = -40°C to 125°C		 133 μA
IQ Quiescent current into VOUT; IOUT= 0 mA,
VEN = VIN = 6 V, VOUT = 5 V, PFM
Tj = -40°C to 85°C		 5 9 μA
IQ Quiescent current into VOUT; IOUT= 0 mA,
VEN = VIN = 6 V, VOUT = 5 V, PFM
Tj = -40°C to 125°C		 17 μA
ISD Shutdown current VEN = 0 V; Tj = -40°C to 85°C;
VIN = 5V		 2 12 μA
ISD Shutdown current VEN = 0 V; Tj = -40°C to 85°C 26 μA

What does "into VOUT" mean please? Putting power or voltage back into the device at Vout doesn't seem like a good idea to me! At least according to all buck/boost topologies from books.

The quiescent current with 5V fed into Vout is much less than with the chip in shutdown.

Please can anyone clarify, and pass along any tips on minimising current when the chip is in shutdown?

Regards,

Rob.

  • 0
    TI__Mastermind 20900 points
    Hello Rob,

    some of the internal blocks are connected to VOUT. Therefore there is a current flowing into the VOUT pin (from output cap). The energy will be transferred from input to output during switching. Note, Iq is defined while the device is not switching.
    Please have a look into this article: www.ti.com/.../slyt412.pdf

    best regards,
    Julian
  • 0 in reply to Julian Hagedorn
    Prodigy 100 points

    Thanks Julian,

    and I see that the app note link you sent is also in the app note list on the main TPS63070 web page. The 2nd set of figures given for Vout quiescent are the amount the device will draw from the output filter capacitor in between switching cycles on my understanding.

    Fortunately I don't have to worry about the 125C quiescent figures, as the application is for 50C max ambient with 100mA load, running low duty cycle.

    The 26uA max shutdown current is spec'd at 16V, 85C. I would hope at 10.5V, 50C it would be lower? The system runs from 7 large alkaline batteries in series.

    Regards,

    Rob.

  • 0 in reply to Robert Brown66
    TI__Mastermind 20900 points
    Hello Rob,

    at lower temperatures the shutdown current is lower. Up to 50C ambient it the shutdown current is 14.3uA max.

    regards,
    Julian
  • 0 in reply to Julian Hagedorn
    Prodigy 100 points

    Thanks Julian,

    I'll drop 14.3uA into my estimate of system shutdown current. The circuit is an update on a previous one with the TPS63020 that wanted a higher supply range.

    I think you can close down this thread now ?