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BQ24297 DPM flag : what does it sign?

kellerman
Prodigy 50 points
Other Parts Discussed in Thread: BQ24297

Chapter 9.3.2.2 of the BQ24297 datasheet explains DPM.

Figure 14 makes a difference between DPM- and supplement mode. Is this  true?I do not think so

Isn't  the supplement mode also part of the DPM mode?

If you enter supplement mode (SYS < VBAT;  I(BAT) > 0 ) , the DPM flag of Reg08[3] remains still acive. 

Looking to Fig 14, DPM flag is active during the phases DPM   AND  supplement. Is this correct?

It would be helpful to draw the state of the DPN Flag into Figure 14.

  • 0
    TI__Guru 57811 points
    Referring to 9.3.2.3, supplemental mode refers to when the system voltage falls below the battery voltage, the BATFET turns on and the battery discharges. It may happen with or without DPM.
    When only battery is present, battery discharges to suports the system voltage, i.e. supplemental mode.
    In DPM, when the charge current is reduced to zero, but the input source is still overloaded, the system voltage starts to drop. Once the system voltage falls below the battery voltage, the device automatically enters the supplement mode, i.e. battery discharges to support the system voltage.
    Thanks!
  • 0 in reply to Ning T
    Prodigy 50 points

    Thanks for your answer.

    Regarding the supplement mode, a agree to your definition as refered acc. 9.3.2..

    I did some additional measurements: The bit Reg08[3] (DPM_STAT) is always active in supplement mode.

    It turn on before supplement mode (VSys < VBat) is reached and before any limitation by I(in) or VBus can be measured.

    From this point of view , the following  questions are  remaining :

    - is it's naming not optimal or misleading?

    - how accurate does it signal the DPM mode ?

    - is the definition of DPM mode 100% correct or does it begin before any limitations could be measured 'outside ' the device? ( this may be a subject for a new thread)

    Best regards

      

  • 0 in reply to kellerman
    TI__Guru 57811 points

    The input VBUS supports both the system load and charging current. The system load has higher priority over the charging current. When input current DPM happens, the charging current will be reduced first so that the input may support the full system load demand. If the charging current is reduced to 0A, but the input is still over-loaded (i.e. in DPM), the battery will discharge to support the system load (i.e. supplement mode) together with the input to prevent the input voltage from dropping. In this situation DPM and supplemental mode happen at the same time, so Reg08[3] (DPM_STAT) is still active. Please refer to page 20 and page 21 for the details. Thanks!