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.

bq24171 / DPM function

Other Parts Discussed in Thread: BQ24171

Hi All,

Let me ask about DPM function. In fig.10 in datasheet, IOUT is reduced due to DPM function, then I'd like to the operation when the ISYS will go up more and IOUT will go down below zero. Does the IIN remain 3A (IDPM) and turn on BATFET to discharge battery?

Best Regards,

Sonoki / Japan Disty

  • Hi,

    I would appreciate if you response to this post. Thanks in advance.

    Best Regards,

    Sonoki

  • Hello Sonoki,

    Typically the feature that you are asking about is called "Supplement Mode" in other chargers. Looking at how the BATFET operates and reviewing other aspects of device operation it appears that the only way to have the battery provide additional power to what is provided from the adapter to the system load is to have the system load attached directly to the battery rail as discussed on Pg. 2 of the datasheet.

    The discussion of the "System Power Selector"starting at the bottom of Pg 18 of the datasheet discusses how the power provided to the system rail in Figure 1 is an exclusive OR so that ACDRV and BATDRV are never closed simultaneously in fact a dead time is incorporated to prevent shoot-through.

  • Hi Ryan-san,

    Thank you for your comment. I understand that the ba2417x can be in supplement mode if it's configured like Fig.2 in Pg.5 of bq24171 DS. However I'm not sure the case of the multi-cell application configured like Fig.1 in Pg.4 of bq24171 DS. In this case, the DPM current (IDPM) is set to 3A, so the input source can provide the total current up to 3A for system and battery. So now I'd like to discuss about the case of "IDPM < Isys". Following is my expectation at "IDPM < Isys" is happened.

    • System require 3.5A.
    • Vsys is dropped because the input power is limited (IDPM=3A in this case).
    • Vsys is dropped below Vbat, then the body diode of Q3 is turned on and battery start to provide (discharge) 0.5A for system

    Is my understanding correct?

    Best Regards,
    Sonoki

  • Hello Sonoki-san,

    In the case where the adapter voltage is below the battery voltage the device will be in sleep mode. Also is discusses how the transition between the Q1/Q2 and Q3 is a break before design so that there is never a direct conduction path through all three MOSFETs.

    This is to prevent reverse discharge cases.

  • Hi Ryan

    I have a simple question, I want to know what's the main function of the VINDPM and IINDPM?

    Thanks for your reply!

    Xuehao
  • Hi Xuehao,

    Dynamic Power Management is a control loop that monitors the input voltage or current. The main function is to keep the input from crashing due to a large power draw from the system. This is done by monitoing the input voltage (VINDPM) or the input current (IINDPM) and then limiting or reducing charge current. These are two different DPM methods and are well explained in the literature, Dyanmic Power Management for Faster, More Efficient Battery Charging.

    If you have further questions after looking at the document, then I can help clarify!

    Literature link: http://www.ti.com/lit/an/slyt546/slyt546.pdf

    Best Regards,

    Joe

  • Hi, Joe

    Thanks for your reply!
    I meet another question when i learn the datasheet (page 16)about typical charging Profie.
    In the constant Voltage charging phase, I want to know who is the constant voltage ? Does it refer to Battery Voltage or the Buck output Voltage? and why does the chaging current drops, what's the principle of it ? Is it related to the working condition of MOSFET Q3?
    I wish i can get your answer!

    Xuehao
  • Xuehao,

    Your questions are no longer directly related to this thread. In the future please post a new question on the forum. That way if someone has a similar question in the future, they can just refer to that thread. It helps everyone in the long run.

    xuehao yin said:


    In the constant Voltage charging phase, I want to know who is the constant voltage ? Does it refer to Battery Voltage or the Buck output Voltage? and why does the chaging current drops, what's the principle of it ? Is it related to the working condition of MOSFET Q3?

    The constant voltage refers to the output of the charger, or the buck output, which is also tied to the battery.

    The way constant current constant voltage charging works is the charger will provide constant current (fast charge current) to charge the battery to the desired voltage level (regulation voltage). Once the voltage level is reached, that voltage level is held constant. The current needs to decrease in order to hold the voltage constant. To reach the most battery capacity, the current is gradually declined until it is ultimately terminated and the battery is done charging.

    For a more in depth look at Constant Current Constant Voltage charge profile, refer to this document starting on page 12 is the Li-Ion charge section.

    http://www.ti.com/lit/an/snva557/snva557.pdf

    Regards,

    Joe