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Designing DC-DC converters using TI TPS61200 controller

1.2V to 5V DC_DC converter based on TI TPS61200

1.2V to 5V DC_DC converter based on TI TPS61200

About a year ago, while researching low startup voltage DC-DC converters I ran into Texas Instruments’ TPS61200. This monolithic synchronous rectifier boost converter has several nice features. First, the input voltage range starts at 0.3V; therefore, it’s possible to run the converter from low-voltage source such as single solar cell or supercapacitor. Second, the converter is powerful – up to 1.8A for certain input/output voltage combination. (“Certain” is a key word here – see below for explanation). Another nice feature is the ability to down-regulate the output when Vin exceeds Vout; for example, you can configure the converter to run from single-cell Li-ion/Li-poly battery and output stable 3.3V over the whole 4.2V-2.7V Li-Poly range. In addition to all that, the controller has built-in undervoltage lockout feature – minimum input voltage, below which controller would shut itself off can be set with simple voltage divider. This feature comes handy when rechargeable battery is used as power source. TPS61200 also has pins for enabling/disabling and power-saving mode on/off. Device is manufactured in 2 fixed Vout configurations – 3.3V, 5V, plus adjustable variant. Maximum working input voltage is 5.5V, minimum output voltage for adjustable part is specified at 1.8V.

After much prototyping and testing I came out with a layout that works well. The result can be seen on title picture – Arduino Duemilanove board (running USB keyboard polling sketch ) , USB Host Shield, LCD display and USB keyboard all powered by single 1.2V NiMH AA cell. The circuit that makes it possible can be seen on the left side of the picture connected between the battery and USB B connector, which is used here as 5V power connector to the Arduino.

The run time of this setup from freshly charged 1800ma NiMH cell is 6 hours which makes it quite practical. It should be noted that when input voltage is much lower than output voltage, efficiency suffers ( see figure 8 in the datasheet. 3 NiMH cells in series or single-cell Li-Poly is much better for 5V output, even 4 NiMHs will work if load is light – in down conversion mode power losses in the converter increase and I found that the chip gets very warm with output current of 200ma or more while down converting.

LiPo33 closeup

LiPo33 closeup

Another non-obvious characteristic of this controller is maximum possible output current to input voltage relation. Figure 1 in the data sheet shows that for input voltages up to 0.6V output current is really small – less than 50ma. This is the current one should expect while running the converter from single 0.55V solar cell. Voltage drop due to battery discharging shall also be considered. For example, fresh Li-Poly cell has 4.2V terminal voltage. According to Figure 1, this gives output current of 1500mA. However, at the end of discharge (2.7V) max.output current drops to ~800ma and this current should be taken as maximum for the whole range.

The controller has built-in over-current and over-temperature protection so experimenting with heavy loads won’t kill it. I found it running not too hot with output current up to 1A. More current is quite possible when input to output voltage ratio is small and cooling is adequate.

Now let’s talk about choice of power sources. A pair of AA or AAA alkaline batteries will make good source for 3.3V generation. 3 will work well for 5V. As little as one can be used if weight and/or volume of a circuit has to be reduced. Absolute max.input voltage for TPS61200 is specified at 7V, therefore, for maximum run time a series of up to 4 AA cells can be used with big loss of efficiency at the beginning of discharge, until input voltage drops below output voltage. Also, solar cells and super capacitors can be used when loads are really light. Rechargeable batteries are another good option; however, since TPS61200 is capable of working with input voltage down to 250mv, special precautions must be taken when using rechargeables with this controller.

Draining rechargeable cell below its end-of-discharge voltage may cause damage to the cell. As a result, a cell may become non-rechargeable and Lithium cell may even overheat and catch fire. For NiMH cell, end-of-discharge is 0.8V; for Li-Poly cells recommended end-of-discharge is 2.5-2.7V. To work properly with rechargeable power sources TPS61200 has built-in undervoltage lockout circuitry – when voltage on UVLO pin drops below 250mV, the converter turns off. Therefore, desired end-of-discharge voltage can be easily set with voltage divider ( R3, R4 of the schematic). UVLO pin also has hysteresis of 50mv and this hysteresis gets multiplied by dividers’ ratio; for example, when UVLO is set to 2.5V, minimum turn-on voltage of the converter will be 3V. Capacitor C4 takes care of this issue by shorting resistor R3 during turn-on.

The closeup picture shows TPS61200-based DC-DC converter designed for 5V output and Li-Poly input. Blue part marked “0″ close to the low right corner of the PCB is a jumper across R5 (I’m using fixed-otput TPS61202 here) and two resistors placed along the edge of a board make UVLO divider. JST connector polarity is compatible with Sparkfun single-cell Li-Po batteries.

Project files can be downloaded from Downloads section. Also, PCB is available at BatchPCB. TPS61200 comes in 10 pin QFN package with thermal slug on the bottom of the package, which has to be soldered on the PCB for proper cooling. Other parts are size 0603 and 1206. Both surface mount and through-hole JST connectors can be used on the input side.

I’m getting ready to start producing this converter in 3.3V and 5V variants with 0.8, 1.6, and 2.5V end-of-discharge voltages. Please let me know if any other output or end-of-discharge voltages are necessary. Also, any other comments about this design are most welcome!

Oleg.

Related posts:

  1. TPS61200 board modifications. Part 1 – changing undervoltage lockout

30 comments to Designing DC-DC converters using TI TPS61200 controller

  • Sergey

    Здравствуйте Олег!
    Вы случаем не в Москве живете?
    Сколько это будет стоить?
    И какой максимальный ток при использовании 2-х D-size батареек?
    Заранее спасибо.

    • Здравствуйте, Сергей.

      Я живу в Колорадо. Стоить такой конвертер будет долларов 10-15. Максимальный ток в начале разряда при напр. на входе 3В и выходе 3.3В будет примерно 1.5А, при выходе 5В – 900мА.

      Олег.

  • Sergey

    Здравствуйте Олег!
    Спасибо за быстрый ответ.
    С удовольствием купил бы, да живу в Москве.
    Далеко очень.
    Ежели с оказией какой…
    С уважением.
    Сергей.

  • trl

    Great article Oleg!

    Can a voltage monitor be added to support a pre-turn-off interrupt output? Thanks!

  • Aaron

    I’d be interested in a perhaps 5-10 of the 5v version of these. However I would like to be able to have 1A max current available through the whole life of the battery. Perhaps setting the end-of-discharge voltage to 3v would achieve this, and from what I can see, most Li-Poly cells drop quite sharply in voltage after the 3v mark anyway. Thanks.

  • Mac

    This will be a great board. I mostly have switch completely to LiPo as primary batteries since single chip usb/external charger are out. And what about an lipo power board with both charger and voltage regulation?.

  • Marek

    Hi!

    I have a silly question. You wrote that UVLO pin also has hysteresis of 50mv and this hysteresis gets multiplied by dividers’ ratio. My question is, what do You mean under by dividers’ ratio? Do You mean voltage dividers’ (R3 divided by R4) ratio or do You mean currently used UVLO divided by internal reference threshold 250mV? For example, if I’m using 3V, then ratio should be 3/0.25=12.

    Thanks in advance!
    Marek

    • Hysteresis means that in order to switch the converter on after UVLO has tripped you need to apply UVLO+50mv, i.e., 300mv typical. If, say, you want UVLO to trip at 2.5V, then your divider ratio would be 10 (2.5/0.25) and to turn converter on you’d need to apply 3V – you’ll have 0.5V difference between turn-off and turn-on voltages. If you want UVLO to trip at 3v, ratio becomes 12, then turn-on voltage would become 3.6V – the 0.6V difference. At some point, turn-on voltage becomes larger than slightly discharged battery would be able to provide, that’s why I placed a capacitor across upper resistor of UVLO divider – to short UVLO to VIN during power-on.

  • Peter

    Hi Oleg!

    Thanks for posting such a helpful article on the TPS61200. I am working with it on an application which involves getting power from extremely low voltages (like ~100mV). I read on some websites (http://www.eetimes.com/electronics-products/analog-products/4092376/REVIEW-300-mV-input-voltage-boost-converter-throttles-micro-fuel-cells?pageNumber=0) that the power management can be done down to zero volts if the UVLO is tied to the output. Is that possible? Sorry for the weird question, but thanks in advance!!!

    Peter

    • It is probably possible, but what would be the application? At 0.3V Iout is very low (10ma max) and efficiency is bad, any lower than that and you will be just heating air.

  • Bert

    Hi Oleg!
    I want to know the value of the inductance which you have used.and the maximum value of the inductance which connected with TPS61200.and how you get it?
    thank you very much!

    • Have you looked at the schematic yet?

      • Bert

        Hi Oleg!
        I have kooked at the schematic,it said that the value of the inductance should be at 1.5uF to 4.7uF,and he give the reason for the minimum value,but i want to know the reason that how we get the maximum value.
        In addtion , I choose a 10uF inductance, and it get better efficiency and minimum start voltage when i choose 0.4v for my input voltage.
        In a word ,I want to know how the inductance affet the IC. and how he get the maximum value of inductance.
        Sorry for my poor english,thank you for your attention,Best wishes.

        • Have you looked at the datasheet yet? There is no maximum value of inductance per se, you choose it based on size/availability. Step response gets slower with increasing inductance too.

          • Bert

            Thanks for replying so soon,
            At the datasheet the reccommended inductor value range is between 1.5uH and 4.7uH.How he get 4.7uH for the inductor? Have the inductor affect the output current?
            Best wishes

  • Charles

    Hi Oleg!
    DO you know why the datasheet reccommended the inductor value is between 1.5uH and 4.7uH?and how the inductor affect the output current?
    Best wishes

    • The recommendation is a summary of results of a formula given right next to it. If you want to know why you use the formula; if you don’t care just use recommended values.

      Inductor affects output ripple, the smaller it is the bigger the ripple. It also helps when an inductor is rated higher than peak current, otherwise it will overheat, lose inductance and/or melt down.

  • Striker

    can it work on pwm based pic controller ?

  • Eric

    Oleg, BatchPCB is gone… It looks like everything from their old site is now on OSHpark.com but the new site has no search facility, google can’t seem to find any mention of “TPS61200″ or “Lipo33″ on their domain, searches for “DC-DC” and “DC to DC” failed to find your board. Do you know if your great little board made it to OSHpark? Have the link? Thanks for designing and sharing this TINY implementation. Eric.

  • Eric

    I was just there. The sparkfun board looks considerably longer than what you picture above, wouldn’t fit my current project unless I cut the JST connector off, repaired the traces/via I cut/remove. Is the sparkfun board your design, just on a different shape board? I’d much rather start with your board if its shorter, avoid the re-work. (My case is 21mm wide, so I’d like the board to be no longer than that.)

    • I was one of the designers of rev.1 of SF board. There is another pair of output pads right next to JST connnector; it seems you can just cut the PCB between the connector and the pads. There is one trace which would have to be reconnected.

  • lou

    Very nice design. Could you post a few closeups of the driver board and how you attached it to the aluminum rails.

    Thanks, Lou

  • John Wayne

    Do you guys have any board that takes 3.7V cell and converts it to 3.3V with 600mA or more current.

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