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BQ24072T: Design Questions

MB9265
Prodigy 60 points
Part Number: BQ24072T

Hi,

I have a design that uses the BQ24072T with a 5V 1.2A power supply and Li-ion 3.7V 1200mAh battery and had a few questions:

  1. How well does the IC performs with a lot of capacitance on the output versus the input?
  2. How quickly does it react to overcurrent?
  3. Is there any type of slow-startup or limiting current at startup?
  • 0
    TI__Mastermind 23200 points

    Hi,

    Welcome to E2E!

    MB9265 said:
    How well does the IC performs with a lot of capacitance on the output versus the input?

    At the input, you'll see some inrush that will be charging your input capacitors. At the output, you'll see the device charge the capacitors as well. There shouldn't be an issue on the amount of capacitance. The values shown in the Application Diagram portion of the datasheet is recommended. You can find more in Section 10.2.1.2.8 Selecting IN, OUT, and BAT Capacitors. How much capacitance are you expecting? 

    MB9265 said:
    How quickly does it react to overcurrent?

    This will vary from device to device but I expect within ms range. I can reserve some time to look at this in the lab 

    MB9265 said:
    Is there any type of slow-startup or limiting current at startup?

    Yes! In either of the USB modes, the device will operate within USB-IF compliance meaning it allows 10uF to be hard started. It'll then establish 50uC as the maximum inrush charge value. You can find more on this information in Section 9.4.1 Input Source Connected (Adapter or USB). I've tested this compliance with 2200uF and 4700uF capacitors at the OUT pin. 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 60 points

    Thank you for your response! I have a few follow up questions/comments.

    Anthony P Pham said:
    At the input, you'll see some inrush that will be charging your input capacitors. At the output, you'll see the device charge the capacitors as well. There shouldn't be an issue on the amount of capacitance. The values shown in the Application Diagram portion of the datasheet is recommended. You can find more in Section 10.2.1.2.8 Selecting IN, OUT, and BAT Capacitors. How much capacitance are you expecting? 

    There is 20uF at IN, 10uF at BAT and about 40uF at OUT. There is an additional 220uF downstream in the circuit

    Anthony P Pham said:
    This will vary from device to device but I expect within ms range. I can reserve some time to look at this in the lab 

    This would be very helpful.

    Anthony P Pham said:
    Yes! In either of the USB modes, the device will operate within USB-IF compliance meaning it allows 10uF to be hard started. It'll then establish 50uC as the maximum inrush charge value. You can find more on this information in Section 9.4.1 Input Source Connected (Adapter or USB). I've tested this compliance with 2200uF and 4700uF capacitors at the OUT pin.

    The design I am working with does not use the USB modes (EN1=0, EN2=1), would this still apply?

  • 0 in reply to MB9265
    TI__Mastermind 23200 points

    Hi,

    MB9265 said:
    There is 20uF at IN, 10uF at BAT and about 40uF at OUT. There is an additional 220uF downstream in the circuit

    These are all fine values! 

    I'll be reserving some time tomorrow to run some tests to get you the the appriximate time for the ILIM to occur.

    MB9265 said:
    The design I am working with does not use the USB modes (EN1=0, EN2=1), would this still apply?

    The USB IF compliant only applies to either of the USB modes. 

  • 0 in reply to Anthony P Pham
    Prodigy 60 points

    When not in any USB mode, what type of inrush or overcurrent protection exists?

  • 0 in reply to MB9265
    TI__Mastermind 23200 points

    Hi,

    When not in USB mode, the device will limit the current to the programmed current setting based on the resistor on the ILIM pin. You should expect this current limit to kick in about 1 ms

    Best Regards,

    Anthony Pham