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bq24079 OUT pin creating +/-5V supplies

MarcosCba
Prodigy 140 points
Other Parts Discussed in Thread: TPS61020, BQ24079, TPS63700, LM117, INA128, OPA177, TPS61220, TPS61070, TLV700, BQ24073, TPS61073, TPS60403

Chris:

          Hi, Thanks for your fast answer! Here is the thing… I’m implementing a circuit feed by a Li -Ion battery (3.7V / 850mAh).  This battery should power a circuit that needs -5/+5 [V] source and consume less than 200mA. I use BQ24079 for charging the battery form USB port. As BQ24079 out is VBAT (3.7 V) when USB port is disconnected and less than 5V with USB port connected (as you just told me), I decided to use TPS61020 and TPS63700 at BQ24079 output to produce the -5/+5[V].  The configuration of TPS61020, TPS63700 and BQ24079 are the following:

·         TPS61020

o   R3= 1,62 MΩ

o   R4= 180KΩ

o   Not implementing LBI/LBO. LBI=GND, LBO = unconnected.

o   C3= 47uF

o   C2=2.2uF

o   C1=10uF

o   L1=6.8uH

 

·         TPS63700

o   As “Figure 14. Circuit for –5 Volt Output” page 13 of the datasheet.

·         BQ24079

o   IN = 5V (USB port)

o   BAT = 3.7 V, 800mAh Li-Ion Battery

o   EN1=Hi;EN2=Low à USB500mA mode (So ILIM unconnected)

o   Ichg=300mA (ISET) à Riset= 2.94 K (at 1%)

o   SYSOFF not implemented à GND.

o   TMR= default values à unconnected

 

The block diagram of the Circuit is:


 

And here comes the questions:

1.          1. Is this design correct or will not work at all?

2.           2. will I have regulated -5 V at TPS63700 out and +5 V at the TPS61020 out although Vin for this circuits (BQ24079 out) varies from 3.7 (Vbat) to 4.5 (aprox., depends on the     current as you explain me in your last post). I suppose yes, because is a retroalimented circuit… but to be sure.

3.3     3. Do you have any experience using BT50 li-Ion battery (The one use in cell phones) with the BQ24079, because I’m thinking using that one.

 

 It is the first time I do this kind of designs so I am a bit lost…

Thank you very much in advance,

Marcos

 

  • 0
    TI__Guru**** 150760 points

    Marcos,

    I split this into a separate thread since this is basically a new topic.

    Yes, your configuration should work as you have it, but it may not be optimal.  What are the load requirements on your +/-5V rails?  Is it 200 mA on each rail?  Will you have another input besides USB?  An adaptor?  Each of these ICs is very oversized for a USB input.

    Yes, each of the ICsw will regulate their output to the set value even if their input voltage changes.  This is how they operate.

    I don't have any experience with that particular battery.  Just make sure that its capacity is high enough for enough run time in your system and that it can provide the peak current required by your load. 

  • 0 in reply to Chris Glaser
    Prodigy 140 points

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    Chris,

                    Hi again! Thanks for answering.

    Chris Glaser said:

    What are the load requirements on your +/-5V rails?  Is it 200 mA on each rail?

    The -5/+5 rails are used to power a very simple signal conditioner made with an INA128 and OPA177 (Configuration: Trimming of Output Offset Voltage). Also the +5 V rail powers an ARM7 microcontroller (Actually powers an LM117 regulator which feed ARM7 with 3.3V).

    A measured both rails and -5 consume practically 0A (less than 10 mA) while the +5 rail consume around 150mA in the worst case.

     

    Chris Glaser said:

     Will you have another input besides USB?  An adaptor?  Each of these ICs is very oversized for a USB input.

     No, it would be just the USB input; I use it for battery charging and also to communicate the PC with the microcontroller.

     


    Under these conditions will this design work ok?

     

     

    Thanks for Battery advise, I’m going to investigate a little more about it.

     Marcos.


     

  • 0 in reply to MarcosCba
    TI__Guru**** 150760 points

    Marcos,

    Thank you for confirming your load requirements.  Based on this, I would not use either the TPS63700 or TPS61020 for your system.

    For such a small -5V supply, the TPS6040x series of inverting charge pumps work best.  They would run off the regulated 5V input and simply invert it to give you a cheap and simple -5V rail.  Just pick the frequency option among the 40xs that is best for you.

    For the 5V boost, the TPS61070 series or TPS61220 would be smaller, cheaper, lower power options.  The TPS61220 may be too small if your total load is more like 160 or 170 mA, instead of around 130 or 140 mA.

    Instead of the LM117, I would check out our new TLV700 series value LDOs.  These are brand new, have great specs, and yet quite cost competitive.

  • 0 in reply to Chris Glaser
    Prodigy 140 points

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    Chris:

                    Thanks for the advisees! I was analyzing the IC you recommended to me and seems that they will work perfectly in my design. Just to be sure I measured the consumptions of my circuit again and obtained the following results:

    ·         +5 rail:

    o   Worst Case with USB connected: 130mA. This major consumption appears when transmitting information between microcontroller and PC.

    o   Worst Case with USB disconnected (Working from Battery): 110mA.

    ·         -5 rail:

    o   Worst Case: 1,5mA. It does not matter if USB is connected or unconnected

    Based on these results the IC that you recommended should work correctly.

    I have some doubts in the design of the circuit for TPS6107x:

    • In the TPS6107x datasheets states that “Due to the nature of boost converters, the output voltage regulation is only maintained when the input voltage applied is lower than the programmed output voltage”. If I use BQ24079 with USB  connected the BQ24079 output will be approximately 5V which is the output I need at TPS6107x out. Can this bring me troubles? Should I use BQ24073(Voreg=4,4V) to avoid problems? I’m not implementing SYSOFF nor TD so this does not influence the decision of which integrated to use.
    • I decided to use TPS61073 which has the power save mode function. This function just presents advantages or can bring some disadvantages?

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    Doubts about TPS6043: Can I take the input to TPS6043 from TPS61073 output?

    The configuration of TPS61073, TPS6043 and BQ24079 are the following:

    ·         TPS61073

    o   R3= 1,62 MΩ

    o   R4= 180KΩ

    o   C3= 100nF (Datasheet recomendation)

    o   C2=2x4,7uF(0603)

    o   C1=2x4,7uF(0603)

    o   L1=6.8uH

    ·         TPS60403

    o   CI=1uF

    o   C(fly)=1uF

    o   CO=1uF

     

    ·         BQ24079

    o   IN = 5V (USB port)

    o   BAT = 3.7 V, 800mAh Li-Ion Battery

    o   EN1=Hi;EN2=Low à USB500mA mode (So ILIM unconnected)

    o   Ichg=300mA (ISET) à Riset= 2.94 K (at 1%)

    o   SYSOFF not implemented à GND.

    o   TMR= default values à unconnected

    Block diagram:

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    1.       Is this design correct?

            Thanks In advance, Marcos.

     

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    Ps: I can’t change LM117 because it comes integrated in the microcontroller PCB. But I'm going to take your advice for followings designs.

     


  • 0 in reply to MarcosCba
    TI__Guru**** 150760 points

    Yes, using the bq24073 with an OUT voltage of 4.4V would probably be best.  In all likelihood, it would still work with the 079, since there are losses in the circuit from the USB input to the 5V output that reduce the input voltage and allow the TPS61073 to still work in normal boost mode and boost the input.

    For the capacitors in the circuit, consider the DC bias effect, whereby the ceramic capacitor loses its effective capacitance as the DC voltage on it increases.  Thus, I would recommend that all your ceramic caps be at least 10V rated.  5V on a 6.3V cap reduces its effective capacitance by as much as 80%.  You might add one more output cap just to be safe.

    Yes, the TPS60403 can run off of the regulated 5V output of the TPS61073.

    For the bq24073/9, make sure to connect all the other pins (TS, IN, etc.) per the instructions in the datasheet.  I would add a 1k pull down on ILIM since the datasheet notes that leaving it floating disables all charging (page 6).

    Be sure to follow the layout recommendations given in the datasheet, especially for the TPS61073.  You can also order the EVM for all 3 of these devices and build that first with your components and debug your design.

  • 0 in reply to Chris Glaser
    Prodigy 140 points

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    Thank you very much for the help!! I am going to take all the last recommendations for the circuit.

    As soon as I finished my circuit I will let you know how all worked out

    Thanks again, best regards,

    Marcos.

  • 0 in reply to MarcosCba
    Prodigy 140 points

    Hi chris! I finally built the circuit and it works perfectly! Thank you very much for your assistance!

    Best regards! Marcos.