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BQ24070: General ? about architecture of battery charging and power management

DJH
Intellectual 985 points
Other Parts Discussed in Thread: TMS320DM365, TPS65053, BQ24040, BQ24070, BQ24072, BQ27200

I am trying to figure out how best to configure my system based on the requirements.  I have an embedded battery system that will be recharged via USB.  The power management IC I would like to use is the TPS65053 (the processor is the DaVinci TMS320DM365).

I originally had planned to use BQ24040, but it turns out that I would need to handle the switching to connect/disconnect the battery to the BQ24040.  I'm now leaning towards using the BQ24070 because it appears it can handle simultaneous battery and USB power and charge the battery without any external switching required.

My questions are both general and specific.  Generally I'm looking for a pat on the back or a slap on the hand; does using the BQ24070 with the TPS65053 make sense in this case and do they play well together?  Am I correct in thinking that the battery will only be connected to the BQ24070 and that the system will be powered via the OUT pins, as shown in the datasheet page 1?

Specifically I'm not clear on the TS, what is Vout when running off the battery, and more on the DPPM.  I don't have a temperature sensor in the battery.  I have seen some documentation that indicates that pulling TS high via a 10K resistor disables the TS pin.  Is that correct?

The specs for Vout when USB is plugged in is pretty clear, but is Vout simply the voltage across the battery when no USB (power input) is present?  There is a section on page 13 (Case 2) that casually mentions this, but I'm looking for confirmation.

It's not clear to me how, or if, DPPM has any affect or anything when operating from the battery.  Or is it only mean something when USB power is connected.

Many thanks,

David Havell

  • 0
    TI__Guru**** 150820 points

    Yes, you can use the TPS65053 with the bq24070.  The power source (USB or AC adaptor) would plug into the bq24070 and the OUT pin would power the TPS65053 and anything else in the system and the battery would only be connected to the BAT pin.  If you want to be powered from both an AC adaptor and USB, then you might look at the bq2403x family.  The bq24072/5/7/9 are similar to the bq24070 and may provide additional functionality for your system.

    The TS pin expects a 10k thermistor to ground.  If you don't have or don't want to use a thermistor, then a fixed 10k resistor to ground (Vss) essentially disables the TS function.

    The OUT pin is powered from the IN pin or from the BAT pin, depending on which is connected and on the load.  If there is no input source on IN, then OUT is powered from BAT and the voltage at OUT will be the voltage on BAT minus the drop across the internal 40 mOhm FET.

    DPPM reduces the battery charging current so as to not crash the input supply when it cannot deliver all the power that the battery and load are demanding.  So, yes, it is only active when there is a source on IN.

  • 0 in reply to Chris Glaser
    Intellectual 985 points

    Nice, thanks Chris.  You confirm what I have gathered, so I'm going to consider that a pat on the back!  I will mark this as a successful reply because you addressed each of my questions.

    One more related question.  To use the BQ27200 along with the BQ24070, should I put the PACK+ across the 27200 or should I use the OUT pin?  I was planning on connecting it directly across the battery, but you mentioned that nothing else should connect to the battery.

    I do have one other point of question regarding how to switch power off and on; and I'm not sure if I should start a new topic or just continue this one for a bit...

    My device needs to be turned on (connect the load to BQ24070 OUT) for several hours at a time and then turned off (everything except PRTCSS disconnected from the OUT).  Most of the time the device will be in a sleep/low power state but still be 'powered'.  When a button is pressed everything will come to life, do it's thing, and go back to sleep.  But at the end of the day we want to completely disconnect everything (except the PRTCSS) from the battery.

    Can you recommend the best way to switch the load off and on from the OUT pin?  I would like to essentially put a switch on the OUT pins of the BQ24070, but I just wanted to check with you to see if you have a better idea, or if the CE can somehow be used as a switch for OUT (although that appears to not be the case)

    At any rate, thank again for your response and I'll anxiously await your next one!

    David

  • 0 in reply to DJH
    TI__Guru**** 150820 points

    The bq27200 is a pack-side gauge.  It is meant to be implemented in the battery pack.  So, you should consider the battery cells + bq27200 + protection FETs as the "battery" (PACK+ and PACK- pins) and connect that to the BAT pin and Vss of the charger, bq24070.

    What voltage does the PRTCSS require?  If there is a regulator in between OUT and the PRTCSS, then that is a good break point.  Turn the other regulators in the system that run off OUT to off and just leave the regulator powering PRTCSS on.  OUT will still need to be powered to keep that regulator on, so you can't just disable OUT.