Because of the Thanksgiving holiday in the U.S., TI E2E™ design support forum responses may be delayed from November 25 through December 2. Thank you for your patience.

  • State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 64 subscribers
  • Views 47 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ24074: BQ24074 Heat, Power Consumption & Diodes

Chris Boehm
Prodigy 30 points
Part Number: BQ24074

Tool/software:

Hey, I bought the Adafruit Solar charger for testing the BQ24074 IC and I had A LOT of problems with it. Now I am using the EVM Board to get my setting right for the PCB print. Finally I am nearly done. But there are still some  questions in my head to make sure i have understood the BQ24074 IC. 

I am planning to charge my Lipo with a standard Smartphone charger. The Lipo should power a Boost converter which needs 0,5 A (maybe 0,6 for a short time (ca, 0.5 sec)). I also want to be able to use a powerbank to increase the lifetime of my device. In this situation the charging is not necessary but would be nice to have.

I tested the ILIM Mode with I_Lim = 1,460 A and a charging current of I_Charge = 0,,887. I measured the the voltage of R_iset to calculate the charging current over time.  Looks beautiful (see picture below)! BUT: I Set my  power supply to 5V i observed that the current output is the same or even more as the charging current. It follows that more than 0.2 Watt are used somewhere in the BQ24074EVM. But where? Is it heat? Is it normal? Any suggestions to reduce this "power loss"? I need the device to be very safe when it comes to heat.

   

Another question, but I think it goes in the same direction:

In the datasheet FIG 8-12 (see below) Vin is 6V and the mode is USB500, which means a maximum power supply of 3 watts. The graph shows 1 amp at 4V. How can 4 watts be supplied? I have the feeling my math is broken:)

  

Last question:) The Adafruit Solar Charger uses a Diode (SK34D) at the Power Bus of the USB-Input. In my test the voltage drop caused a lot of problem (at least i think the this is the reason:). Do you think i can safely implement a USB-C power supply without using a diode? 




I´m happy about every answer, every tip and every comment :)

Best, 

Chris

  • +1
    TI__Mastermind 25805 points

    Hi Chris, 

    Thank you for reaching out via E2E. Please see my comments below. 

    Chris Boehm said:
    I Set my  power supply to 5V i observed that the current output is the same or even more as the charging current. It follows that more than 0.2 Watt are used somewhere in the BQ24074EVM. But where? Is it heat? Is it normal?

    Power loss internal to the BQ24074 IC is expected. It is a linear charger, so power loss varies based on input to output voltage difference. For example, there will be higher power loss when battery is further discharged compared to when close to fully charged. Power loss due to integrated FETs internal to the IC is dissipated as heat. To optimize thermal performance please ensure you have sufficient vias between the IC thermal pad and the ground plane on your PCB design. The example layout shown on page 41 of the datasheet shows 6 via used for the BQ24074 thermal pad. 

    Chris Boehm said:
    In the datasheet FIG 8-12 (see below) Vin is 6V and the mode is USB500, which means a maximum power supply of 3 watts. The graph shows 1 amp at 4V. How can 4 watts be supplied?

    Thank you for pointing this out. Figure 8-12 is missing a note to clarify the device is not in USB500 mode. The intention of figure 8-12 is to showcase charge current regulation with ICHG set to approx. 1A via RISET = 900ohm. For this case the input current limit has been set above 1A. I will work to clarify this in the next revision of the datasheet. 

    Chris Boehm said:
    Do you think i can safely implement a USB-C power supply without using a diode?

    From the perspective of BQ24074 IC a diode placed before input source is not required.

    Best Regards,

    Garrett