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BQ76920EVM: 充电和放电时Q1、Q2、Q3三个MOS管分别处于什么状态?

?? ?
Prodigy 50 points
Part Number: BQ76920EVM
Other Parts Discussed in Thread: BQ78350
您好，
1.请问BQ76920EVM这个板子的充放电逻辑怎么实现的，充电和放电时Q1和Q2这两个MOS管分别处于什么状态，Q3起什么作用？
2.充电时电流是怎么流的，放电时电流又是怎么流的？
3.BATT端接的12V电池，但PACK+与PACK-之间只有8.8V的压差。
  • 0
    TI__Guru*** 130456 points

    您好 

    1，充放电的时候Q1,Q2应该都是打开状态。Q3作用是precharge MOS，Q3 is a low-cost PCH FET and is used to keep CHG away from any voltages below VSS. When CHG is not being pulled high, PACK± being pulled below VSS will not be seen by CHG as Q2 does not turn on. Q3 also allows R2 to keep Q1 OFF, since all voltages below this FET can Q3 "follow" PACK± as it goes below VSS

    2，

    红色是充电，蓝色放电。

    3， BATT端接的12V电池，但PACK+与PACK-之间只有8.8V的压差，您量一下电路上哪些元件导致压降。正常充放电MOS关了也不会有3V多的压降。

  • 0 回复 Star Xu
    Prodigy 50 points

    好的明白了，非常感谢您的回答，这对我帮助很大。

    能否再问一下Q6这个MOS管又是起什么作用呢，谢谢！

  • 0 回复 ?? ?
    TI__Guru*** 130456 points

    您好，正在查询，稍后回复。

  • 0 回复 Star Xu
    TI__Guru*** 130456 points

    您好，请参考下面内容

    Q6 is the pre-charge FET.  This FET is controlled by the PRECHG pin of the BQ78350, and it is connected parallel to the CHG and DSG FETs and in series with a 1kOhm resistor (R48). 

    In order to limit inrush current, the BQ78350 will enable Q6 via the PRECHG pin before the BQ79620 enables the CHG FET via the CHG pin.  The inrush charging current will be directed through Q6 and its series 1kOhm resistor, thus limiting the current.  This prevents high currents from damaging any system components.  After a set delay time, the CHG FET will be enabled and then Q6 will be disabled to limit power dissipation during normal operation.