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BQ24038EVM with 12 Vdc input

Oscar Gomez Fuente
Expert 2066 points
Other Parts Discussed in Thread: BQ24038EVM, BQ24038, BQ24172, TPS5420

Hi, I am interesting in use the BQ24038EVM with 12 Vdc input. I have the next configuration:

JMP1: to GND [0.1 mA]

JMP2, pin2 tied to 3.3 Volts of LDO. [AC selection]

JMP3, pin2 tied to 3.3 Volts of LDO. [charger enabled]

JMP5, POP jumper in 1-2 position. [STAT1 led D2 (green) activated]

JMP4, POP jumper in 1-2 position. [STAT2 led D3 (red) activated]

JMP7, NOPOP (selected 4.2 Volts)

JMP6, POP jumper in 1-2 position. [PG led D5 (green) activated]

I connect to the power input 12 Vdc but I notice that the BQ24038  heated too.

Is this normal?

I've read in the data sheet of BQ2403X, than the supply voltage from AC input is min: 4.35 Volts and max: 16 Volts, then I can use a input supply of 12 Vdc.

Than you very much.

  • 0
    TI__Mastermind 36110 points

    You can operate the bq24038 with an input voltage up to 16V.  Please note that the power dissipated in the bq24038 goes up as the input voltage goes up.  The datasheet, paragraph "Thermal Considerations" provides detailed information on this subject.  If your electrical requirements generate too high of a power dissipation, consider using a switching charger.

  • 0 in reply to Matthew Day
    Expert 2066 points

    Whats is the best choice for low EMI, linear topology or switch mode topology?

  • 0 in reply to Oscar Gomez Fuente
    TI__Mastermind 36110 points

    You have asked a very open ended question.  Linear chargers have much less noise than a switching chargers because they do not switch.  Our switching chargers are used by thousands of customers in tens of thousands of applications without any problems.  The noise from a switching charger is very dependent on the board layout.  My suggestion is for you to select a charger that meets your electrical requirements and then follow the EVM layout when you generate your board layout.

  • 0 in reply to Matthew Day
    Expert 2066 points

    Hi Michael, I am finished my design. I am checking each IC. I had again a doubt about V input of BQ24038.

    I've used the BQ24038 only with AC input, I am not going to use the USB input. How do I have to connect the USB input? floating or gnd througth a CAP.

    And I've continued thinking about my old doub. When V input is 5 volts, BQ24038 work ok, but when V input is >= 5 Volts, for example 7 Volts, the BQ24038 I notice that the BQ24038 heated too. I would like use a input of 12 Volts... But if BQ24038 It's working for a long time with a input of 12Volts, Could it be damaged?

    You said me in a previous post:

    You can operate the bq24038 with an input voltage up to 16V.  Please note that the power dissipated in the bq24038 goes up as the input voltage goes up.  The datasheet, paragraph "Thermal Considerations" provides detailed information on this subject.  If your electrical requirements generate too high of a power dissipation, consider using a switching charger.

    The formula is as follows: P(Watts) = (Vin - Vout)*(Iout + Ibat) + (Vout - Vbat)*Ibat

    Vout = 4.2 Volts, Vbat = 3 Volts, Iout = 0.6A and Ibat = 1.25 A.

    With Vin = 12 Volts: P = 12.93 Watts.
    With Vin = 5 Volts: P = 2.98 Watts.
    How can I make dissipation of 12.93 Watts? If I can't make a dissipation of 12 Watts, then I can't use the BQ24038 with Vin = 12 Volts.
    Thank you so much.

  • 0 in reply to Oscar Gomez Fuente
    TI__Mastermind 31120 points

    If not using the USB input you can pull it down to ground with a 1k resistor.  If using it, place at least a 1uF capacitor to ground.

    with higher input voltage the power dissipation goes up, but there is a thermal loop that reduces the charge current if the junction temp gets to 125C.  Therefore, depending on the layout, you will get less current.  The EVM is about the best thermal layout and it can take about 3.5W at 25C ambient before hitting thermal reg, so ~8V of drop gives 430mA.  A typical design has under half the copper and heat dissipation so expect around 250mA with a 12V input.  Will also have to make sure you program the charge time long enough to avoid timer fault issues.

    It would be best to use a switcher (bq2412x) if you want similar charge times with different input voltages.

  • 0 in reply to Charles Mauney
    Expert 2066 points

    Hi Charles,

    The topology of BQ2412X it's different to BQ2403X because BQ2412X no has a System Power-Path Management. With the BQ2438X I can charge my battery and feed my system.

    Any Alternative with S ystem Power-Path Management?

    Thank you so much.

  • 0 in reply to Oscar Gomez Fuente
    TI__Mastermind 36110 points

    You have a few options.  The first is to use a pre-regulator to reduce the 12V down to a lower voltage before applying it to a charger.  You can use a linear regulator, but that will not provide any power savings.  It will only spread the same power across multiple ICs.  You can pre-regulate with a switching power supply and will be able to convert 12V to 5V at approximately 92% efficiency.  The best option is probaby to use a switching charger.  The TPS24170 and bq24172 are switching charger with power path selector.  The switching FETs are internal and the power path FETs are external.

  • 0 in reply to Matthew Day
    Expert 2066 points

    Hi Michael,

    Perhaps as well you say, the best option will be add a switching power supply to convert 12V to 5V at approximately 92% efficiency, because I will can save PCB area, if i use the IC TPS5420 could be a good option.

    With the TPS24172 option I will have to add, transistors, capacitors, diodes, ... I think that the layout will be bigger than the tps5420 option and TPS5420 has an  efficiency of 95 %.

    Thank you so much for your recommendations.