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TPS63070: Use as a battery charger for remote system e.g. weather station

Ted Mawson 3.0
Expert 1795 points
Part Number: TPS63070
Other Parts Discussed in Thread: TPS63802

I'm trying to design a system that runs from a single 3,000 mAHr 4.2 V LiFe battery (the 18650 cells that are commonly available) with a small solar panel charging during daylight as the only supply.  I have several applications that could need the full 2A capability of the TPS63070 but the first one I'm working on uses a small 5V, 250 mA cell (I have other panels if I need more V or A).  I hooked this up to a Sparkfun TPS63070 eval PCB and I have the system powering up in daylight and my next move is to set up for a custom output voltage of 4.2V and then wire in a single cell for testing.  Questions:

1. Will the TPS63070 provide a discharge path to the battery when the solar panel is not illuminated?

2. What will happen if the cell can't provide the current drawn by the battery when it's low? E.g. in the morning the cell will be low and the sun will be weak.  I'm familiar with MPPT concepts but is there an application note or a recommended way to connect the TPS63070, perhaps using the EN pin,  to address this?

3. My project will include a small microcontroller so I'm able to measure voltages (and currents) and take action (including PWM) to adjust the state of control pins on the TPS63070.  The microcontroller will monitor the state of the battery and remove virtually all load from it if it gets low.

Any suggestions on how to achieve my aim, basically using the TPS63070 (or another IC you may recommend) would be much appreciated.

Ted

  • 0
    TI__Mastermind 20900 points

    Hi Ted,

    thanks for the question. Could you confirm your system configuration? I guess that you have: Solar cell -> TPS63070 -> LiFePo -> system

    maybe you could share a block diagram?

    In this case:

    1. in case the device is in shut down mode (EN=low) the input and output are disconnected from each other. TPS63070 does not have an output discharge feature (this is available in TPS630702).

    2. TPS63070 does have a precise EN pin. With this you can set up a precise enable delay. See datasheet section 8.4.2. This appnote might be interesting as well: http://www.ti.com/lit/an/slvae79/slvae79.pdf

    3. ok

    In case the Input voltage stays below 5.5V you could check out our newest device: TPS63802 low quiescent current an high efficient buck-boost converter.

    regards,

    Julian

  • 0 in reply to Julian Hagedorn
    TI__Mastermind 20900 points

    Hi Ted,

    i am closing this thread due to inactivity. Please post back or open a new post for further assistance.

    regards,

    Julian

  • 0 in reply to Julian Hagedorn
    Expert 1795 points

    Sorry for the hiatus.  I tested the 63070 eval PCB and can sort of make it do what I need but it's a hack.  What I really need is a LiPoFe charge IC that takes solar input and applies MPPT techniques to the input (reduces charge current based on the voltage at the input).  If the TPS63070 could be adapted to do this that would be great as the device is a buck/boost which would allow charging when the solar voltage was lower than the battery (4.2V max).

    AD have a device that does this, the LT3562, does TI have anything similar that doesn't cost as much?

  • 0 in reply to Ted Mawson 3.0
    TI__Expert 7925 points

    Hi Ted,

    How do you plan to charge the battery with the TPS63070? Directly with a resistor to limit the current? To add to Julian's answers:

    1. Normally, the TPS63070 can operate in reverse and provide a discharge path for the battery connected to the output. But this could happen only if the set output voltage is lower than the battery voltage and the TPS63070 operates in forced PWM mode. For example, if you set the output voltage to be 4.2 V, and connect a battery charged to a higher voltage, the converter will try to pull down the voltage by sinking the current from the output to the input. This would send reverse current through your solar panel, and could potentially damage it. 
    2. A simple MPPT tracking, assuming fixed MPPT voltage (like with the LT3562), can be achieved by using the EN pin, see this application note:
      Easy solar-panel maximum-power-point tracking for pulsed-load applications
    3. Using the approach from the above mentioned application note, you could monitor the PG pin to stay at MPPT voltage. As soon as the converter enters hick-up mode, the PG output will start oscillating as well. You can then decrease the battery current by modifying the output voltage as described in this application note: 
      Dynamically Adjustable Output Using TPS63000

    I am not aware of a TI buck-boost battery charger with integrated switches and MPPT functionality, but for that it is better to open a new thread an ask the experts for battery chargers ICs (BQ2xxxx devices).

    Best regards,
    Milos

  • 0 in reply to Ted Mawson 3.0
    TI__Expert 7925 points

    Hi Ted,

    We haven't heard back so we assume this answers your question. If not, just post a reply below, or create a new thread if the thread has locked due to time-out.

    Thanks and regards,
    Milos