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TPS61070: Power Save Mode - Efficiencies at 100uA and below

Frank Roberts
Intellectual 355 points
Part Number: TPS61070
Other Parts Discussed in Thread: TPS61291, TPS610981, TPS61099, TLV61220

Hello I have an application where I will be running from 2 AAA batteries and need to generate a 3.3V Output.  The TPS61070 looks to be an idea part for this.  I had a couple of questions regarding this device.

It is a BLE Beacon application in which the typical average current will be ~15-20uA.  It will Transmit every ~2seconds with a Peak Current of ~5-6mA.  In between Transmits it will be in a Low Power mode ~2uA.  My biggest concern is the operation at these low load levels.

1) The 61070 has the Power Save Mode which indicates that at Low Loads it produces several pulses to keep a desired Vout.  What I am not clear on is the Efficiency Graph shows essentially 0% efficiency down at these low load levels?  Should I be concerned about this or is this just a byproduct of how the Power Save mode works?  I.E. - I would have thought the efficiency would still be relatively good in this Power Save Mode.

2) Do you have any data on efficiencies for the TPS61070 with a Vin ~3V (2 AAA's at full capacity) with a Vout = 3.3V?  The graphs only show 2.4V as the highest input voltage.

3) The device will have an ON/OFF switch in which the BLE device will detect a Long Press on the Pushbutton to drive the EN line Low on the TPS61070.  While the TPS61070 provides the ability to disconnect the Load from the Battery I am not seeing that it provides the capability to discharge the Output Cap, possibly I have missed this.  If this is the case and the system enters a very low power mode <1uA a fully charged Output cap could take some time to discharge to where the system truly is shutdown.  Do you have a recommendation on how to discharge the Output cap when the EN line is driven low and that won't cause additional drain during normal operation?  I had thought of just using a N-FET that could be turned on when EN goes low to connect the Output Cap to a discharge Resistor.  I could even use a P-N FET combo in which when the EN line goes low this turns on the P-FET supplying the Gate of the N-FET with Vout turning on the N-FET that connects the Output cap to the discharge resistor to GND.

Thoughts?

Regards,

Frank

  • 0
    TI__Mastermind 46905 points
    The TPS61070 should be not the good solution in your application.
    please have a look at the three device, TPS610981, TPS61291, TPS61099, one of them should be much better than TPS61070
  • 0 in reply to Jasper Li
    Intellectual 355 points
    Hello Jasper. I am sorry but you did not even answer a single question. I am aware of the parts you mention and they are also substantially more expensive than the TPS61070 so unless you have $5K you are willing to donate to me to use these more expensive Boost Converters I would appreciate if you could answer the questions.

    Regards,
    Frank
  • 0 in reply to Frank Roberts
    TI__Mastermind 46905 points
    i just wanted to suggest to best solution to you. i was thinking we should select the suitable device before we dive into detail. if you concerning about the price, TLV61220 may be also a good solution. here is answer to your questions anyway,
    1. the efficiency at very light load condition is not zero, which can be estimated through the application notes "www.ti.com/.../slva828.pdf", "www.ti.com/.../slyt412.pdf"

    2. we don't have the data now. you can try to simulate it in the Webench or apply an EVM for reference.
    3. not active discharge in TPS61070. a p-fet solution can work if the driving voltage of the P-FET is not lower than the 3.3V when disable the P-FET.