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TLV61048: Boost converter to charge a 13V battery from a 5v source

Johann van Niekerk
Prodigy 40 points
Part Number: TLV61048
Other Parts Discussed in Thread: TPS62172, BQ25790

Tool/software:

Looking at a new project and trying to evaluate the solution. 

I have a 13.2 Battery that's only 100mAh capacity that i need to charge. a 50mA continues charger rate is acceptable but could be lower. 

I want to charge this battery from a 5V USB source with the standard 500mA limit. 

My current design looks as follows 

USB>TLV61048>BQ25790Y>BATTERY>TPS62172>3V3

The 12v is needed for a inductive load and 3v3 is SYSV. I am space constraint and the charger does not need to balance the battery just provide protection, ship mode and health. 

This setup would run the TLV61048 to output 14v @1mhz freq 

Apart from making sure the capacitance is large enough to smooth out the supply between the the boost converter and charger, is there any other reason this setup could be problematic ? alternatice parts with smaller footprints/ inductors ?

  • 0
    TI__Guru 67355 points

    Hello Johann,

    The size of the inductor is primarily dependent on the switching frequency and hence the needed inductance. So if you want to minimize the footprint a high switching frequency is preferred. But be careful about power dissipation.

    I recommend making sure that the BQ device starts as late as possible as additional load increases the current demand on the input side of the boost, so if the BQ starts late, you can minimize the input current requirement. 

    And you should be aware that you cannot disconnect the USB voltage from the BQ device as there is a direct path through inductor and diode (no current limit on this connection).

    But from the boost side, you selected a good part.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 40 points

    Thanx Brigitte 

    I understand the USB will be connected at all times to the BQ chip but since the USB is only used during charging and that charge current to the battery is controlled be the BQ chip into the battery, this risk should be minimized ? 

    Good point on the delayed startup. Thank you. 

  • 0 in reply to Johann van Niekerk
    TI__Expert 8660 points

    Hi Johann,

    Is this query related to TPS62172?

    Regards,

    Haseen.

  • 0 in reply to Haseen Reddy Siripi Reddy
    Prodigy 40 points

    Hi Haseen. no not specifically, is there anything I should be aware about ? load is limited on the VSYS side and input is 9 to 14v. my concern was the boost converter and if i needed additional filtering before charger input 

  • 0 in reply to Johann van Niekerk
    TI__Guru**** 169756 points

    HI Johann,

    BQ25790 is a buck-boost converter so no need for input boost converter.  Also, if you are using legacy USB BC1.2 ports (not USB-C) the charger has D+/D- detection that auto sets the charger's input current limit to the USB port's available output current.  The default charge voltage for 3S battery from PROG pin resistor is 12.6V and default charge current is 1A so you will need I2C to reconfigure the charger's I2C registers prior to enabling charging.

    You mention wanting protection features from the charger.  The charger protects against over voltage and over charging but not against over discharge.  The charger expects the battery's protector circuit to protect against over discharge.  The charger will allow the battery to discharge down to 2.5V.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 40 points

    Thanx Jeff! that's what I thought so it will automatically boost and charger 13.2V battery from 5 v source. I had conflicting reports on this. I understand the i2C voltage setup for the battery, and I have dedicated voltage supervisor for the battery low voltage and the battery pack has one. Here is the current configuration 

     

  • 0 in reply to Jeff F
    Prodigy 40 points

      is the setup below sufficient for boost configuration from 5v source?

  • 0 in reply to Johann van Niekerk
    TI__Guru**** 169756 points

    HI Johann,

    The PMID and SYS pins need 0.1uF decoupling capacitors to GND close to the IC.  The BAT pin needs capacitance and PMID bulk caps must not derate after applied voltage below the minimum capacitance values below:

    The ILIM_HIZ pin is clamping the charger's input current limit quite low.  From 5V source to get 1A charge to 13.2V battery assuming no load on SYS, you need more than 13.2V*1A/5A = 2.64A of input current.  The host can disable the ILIM_HIZ pin clamp by setting EN_ILIM=0.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hi Jeff, the battery to be charged is "I have a 13.2 Battery that's only 100mAh capacity that i need to charge. a 50mA continues charger rate is acceptable but could be lower. " so even at 1A charge is excessive. with regards to the capacitance, I'm space constrained 

  • 0 in reply to Johann van Niekerk
    TI__Guru**** 169756 points

    HI Johann,

    Now I remember! Still need the minimum capacitance per the table about after derating for voltage.

    Regards,

    Jeff