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TPS61094: Boost from 3.6V to 5.0V with Super Cap Management

Andrew Pruet
Prodigy 10 points
Part Number: TPS61094
Other Parts Discussed in Thread: TPS63900

I ran across the TPS61094 because I have almost the exact setup of of the following TI article: https://e2e.ti.com/blogs_/b/powerhouse/posts/3-benefits-of-using-a-low-iq-buck-boost-converter-to-extend-battery-life-in-flow-meters. The main difference is that I need a constant Vout of 5V. Up until now, I've been running directly from battery and using a simple boost converter but after I read this article, I realized I needed to add the super cap to protect my battery from the high current draws that occur a couple of times a day when LTE-M is turned on. 

I've read through the datasheet a few times and am trying to understand what would happen if in this diagram below, Vin and Vout reversed (Vin: 3.6V, Vout: 5V) while running in auto boost buck mode. If this were the case, would buck mode never occur and thus the super cap would never be used? If it is the case that the TPS61094 would do little in the area of battery preservation by utilizing a super cap, do you have other recommendations to achieve a similar setup (3.6V boosted to 5V while limiting high current draw on battery)? 

Thanks

  • +1
    TI__Genius 9046 points

    Hi Andrew,

    There are some information you need to know before using TPS61094:

    1. In auto buck-boost mode, EN=MODE=1

    1)When VIN>VOUT_TARGET+100mV&VOUT>VOUT_TARGET&no passthrough, TPS61094 enters BUCK_ON mode. Bypass FET is on so VOUT=VIN, supercapacitor will be charging to VCHG with charging current ICHG;

    2)When VIN drops close to VOUT+100mV. TPS61094 enters supplement mode. In supplement mode, VIN and SUP will supply output simultaneously. Which VIN or SUP has lower impedance will supply its majority of load. To add resistor on battery this will decrease current drawn from battery in supplement mode.

    3)When VIN drops again until VOUT_TARGET+50mV, bypass FET is OFF and TPS61094 enters BOOST_ON mode. TPS61094 supplies output use all power from supercapacitor. No current from battery.

    4)To make auto buck-boost mode work normal, you need VIN>VOUT_TARGET. This means, if you have only 3.6VIN but you want to get 5.0V. TPS61094 would not get in BUCK_ON mode when battery is present.

    2. In Force_buck mode, EN=1 and MODE=0. TPS61094 enters BUCK_ON mode regardless of VIN and VOUT_TARGET. But it cannot automatically enters supplement or Boost_on mode when there is a load needed on VOUT. You need to manually toggle MODE high to make it enters AUTO buck-boost mode

    If you would like to have input current limit and VIN=3.6V, VOUT=5.0V. Maybe you could refer to TPS63900.

    -Wenhao

  • +1 in reply to Wenhao Wu
    Prodigy 10 points

    Great, thank you. I was pretty sure this was the case but my background is not hardware so I wanted to double check.