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BQ76930: 充电问题

user6017574
Prodigy 85 points

Part Number: BQ76930
Other Parts Discussed in Thread: TIDA-01093

两片BQ76930级联监测20S电池。充电MOS和放电MOS管的关断和开启通过MCU分别读取两个BQ76930的CHG和DSG的状态后，MUC控制逻辑芯片（输出12V）来控制MOS管的开和关。在测试充电时发现在关断充电MOS、开启放电MOS时，连接充电器发现可以充电；并且充电MOS发热严重，此时Vgs=3.65V、Vds=3.6V；断开充电器后Vgs、Vds就没有电压了。这是什么原因导致的？

  • 0
    TI__Guru*** 130456 points

    您好，由于问题比较复杂，我需要询问更了解这款芯片的TI工程师，再帮您解答，稍后回复

  • 0 回复 Star Xu
    TI__Guru*** 130456 points

    您好，请参考虾面的内容：

    It looks like the design followed the basic structure of TIDA-01093 for a FET circuit.  The issue seems to be that they should have kept the Q31 of TIDA-01093 so that the charge gate voltage can fall with PACK- when a charger is applied.  As is, with the charger applied at a voltage greater than the battery and CHG_OUT low, the signal from the 12V logic chip which drives CHG_OUT can't go significantly below GND_B, perhaps -0.2V.  D42 and D44 will both be forward biased at perhaps 0.5V each putting the gate of the FET at about -0.6 to -1 V.  VGSTH of the FET is between 3 and 5 V, from the measurement about 3.65 V, so the FET will act as a source follower and the difference between the battery and charger will drop across the body diode of (Q42) and the charge FET (Q43) VGS.

    Include the P-ch such as Q3 in figure 8 of the BQ76930 data sheet or Q31 of TIDA-01093 after the 12V logic chip output.  This will allow the Q42 gate voltage to fall and Q42 etc to stay off when the 12V logic chip output is low.