LTC4040备用电池方案充电故障及出现负载加载后输入电源停用转由电池升压输出的问题

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        在LTC4040的备用电池方案的使用过程中,出现了下列问题。

1、在使用可调电源时,LTC4040的几种工作方式均能正常运行,但在使用外部电源适配器进行供电输入  选用的适配器有以下几种   采样5v 4A输出、单口5v  2.4A输出的适配器,及常用的手机充电器进行供电,但在充电过程中,不接入适配器时,且空载的运行环境下,电池进行升压工作,能正常输出5v,且输入电源故障指示灯常亮;在接入第一种 5v 4a的适配器时和第二种单口5v  2.4a 适配器时和第三种常用手机充电器时,出现复位指示灯和充电指示等闪亮,后期调整输出VSYS分压电阻参数后(在5v输出时,将原有的0.8v电压调整至0.83v后),第一种和第二种充电器能正常为电池充电此时充电指示灯常亮,但在接入第三种常用的手机充电器时依旧出现复位指示灯和充电指示灯闪烁的问题,我当时的解决思路是,可能是因为前期设置的充电电流为2A,充电电流过大,常用电源适配器的输出性能调整较差,导致输出电压下降,与复位比较器的阈值相接近,从而导致指示灯闪亮,后调整充电电流的设定电阻阻值为2K 电流为1A后。前两种适配器均能正常充电工作,但第三种适配器均出现复位指示灯与充电指示灯闪烁现象。

图一:第一种充电器5v -4A

图二:第二种充电器,单口输出5v -2.4A\

图三:第三种充电器,常用手机充电器



三种充电器的输出均采用两线DC接口给到LTC4040输入

2、在使用电子负载进行加载操作时,使用可调电源时,LTC4040可从轻载时的为电池充电随着负载加大,充电电流逐渐减小。且SW引脚波形频率为2.2Mhz,但在使用前两种电源适配器时,在前期负载较轻的模式下,依旧可以为电池充电,但在负载加到1.4a时,出现输入电压相较充电时升高,且控制过压保护的MOS和备用模式反向关断的mos关的Vgs波形下降至1.2V左右,此时SW脚波形变为1.15Mhz的频率,此时出现了电池备用模式启动升压为负载供电,但此时输入的适配器依旧接入,后分析得出,可能是因为输入电源适配器相较可调电源的动态响应性能较差,电压调整时间较慢,导致的当负载变大后,出现暂时电压下降,从而触发PFI引脚的电阻分压比较器阈值,使得控制器误认为输入电源已经故障,将模式切换为备份电池模式,后经过验证将PFI引脚的分压电阻的下端接地电阻R51去除,此时随着负载的增大,SW引脚的频率依旧为2.2Mhz左右,不会出现备份模式,且给电池充电的电流减小,后期将PFI引脚的分压电阻的下端接地电阻阻止加大到130欧姆后,前两种适配器均能带较大的负载。

电路原理图如下图所示,以对NTC电阻R55进行更改为10k

PDF

PCB布局如下图

  • +1
    •  Analog Employees 
    on Jun 24, 2020 8:06 PM 4 months ago

    Hello,

    It sounds like you may just have some power limiting issues. For problem 1, does all work well with no load attached? At what load do you start seeing issues? Does charging work normally?

    For problem 2, it sounds like one of your adapters may be either hitting its power limit or may have a high series resistance contributing to a voltage drop. Adjusting the PFI threshold may help.

    It is a little difficult for me to pick out all of the information from your problem descriptions as I need to translate them to English. Going forward, can you please use shorter sentences and smaller paragraphs to convey the information more efficiently and concisely? Sorry to ask, but it will help both of us solve this faster.

    Your schematic looks good, but it may be worth going through the equations in the datasheet to size the external components to your use case. The values shown seem to be those used for the demo board. This is usually ok, but may not be as optimized as possible.

    Regards,

    Zack

  • Thank you very much for your reply. I'm very sorry. I thought that the Chinese forum could describe the problem in Chinese. The pictures in the previous description may not be displayed properly due to problems with the website upload. I now need to upload it again. During my debugging process In, it was found that when the finger accidentally touches the grounding resistance of the inverting resistance voltage divider of the PFI comparator, the LTC4040 controller resets, the indicator light that resets flashes, and the charging indicator light also flashes. In the test using an adjustable power supply as the input power, the battery can be charged normally without a load. After the load is increased, the frequency of the SW pin of the controller is still about 2.2Mhz, which is in accordance with the normal switch of BUCK mode. The frequency is only when the current sampling resistance of the fuel gauge of the battery is measured and the charging current of the battery is reduced. I think this is a normal working situation, but when the power adapter of the above picture is used, after the load of the rear stage increases The switching frequency of the SW pin of the LTC4040 will be switched from 2.2Mhz to 1.15Mhz, and the voltage of the input power adapter will increase a little. The voltage drop across the R43 and the input sampling resistor is very small, and there is no manual. The 25mV mentioned in the above, but after adjusting the resistance of the voltage divider resistor of the PFI pin, the first two adapters can be loaded normally, and when the power consumption of the load increases, the charging indicator will go out, but the third adapter is still unable to Under no-load condition, the battery is not charged and the charging indicator and reset indicator will flash.

    Figure 1: The first power adapter 5V 4A

    Figure 2: The second power adapter with a single-port output capability of 5V 2.4A

    Figure 3: The third power adapter is a universal mobile phone adapter

    The following figure is the PCB drawing and the schematic diagram of the later adjustment and modification. The parameters after adjusting the device

    PCB

    Schematic 

  • Thank you very much for your reply. I'm very sorry. I thought that the Chinese forum could describe the problem in Chinese. The pictures in the previous description may not be displayed properly due to problems with the website upload. I now need to upload it again. During my debugging process In, it was found that when the finger accidentally touches the grounding resistance of the inverting resistance voltage divider of the PFI comparator, the LTC4040 controller resets, the indicator light that resets flashes, and the charging indicator light also flashes. In the test using an adjustable power supply as the input power, the battery can be charged normally without a load. After the load is increased, the frequency of the SW pin of the controller is still about 2.2Mhz, which is in accordance with the normal switch of BUCK mode. The frequency is only when the current sampling resistance of the fuel gauge of the battery is measured and the charging current of the battery is reduced. I think this is a normal working situation, but when the power adapter of the above picture is used, after the load of the rear stage increases The switching frequency of the SW pin of the LTC4040 will be switched from 2.2Mhz to 1.15Mhz, and the voltage of the input power adapter will increase a little. The voltage drop across the R43 and the input sampling resistor is very small, and there is no manual. The 25mV mentioned in the above, but after adjusting the resistance of the voltage divider resistor of the PFI pin, the first two adapters can be loaded normally, and when the power consumption of the load increases, the charging indicator will go out, but the third adapter is still unable to Under no-load condition, the battery is not charged and the charging indicator and reset indicator will flash.

    Figure 1: The first power adapter 5V 4A

    Figure 2: The second power adapter with a single-port output capability of 5V 2.4A

    Figure 3: The third power adapter is a universal mobile phone adapter

    The following figure is the PCB drawing and the schematic diagram of the later adjustment and modification. The parameters after adjusting the device

    PCB

    Schematic 

  • 0
    •  Analog Employees 
    on Jul 21, 2020 9:02 PM 4 months ago in reply to Misaya

    Hello,

    Does your LTC4040's GND paddle have vias through the board connecting to a GND plane?

    Is PFO toggling during the problematic operation? I wonder if there is a problem with the adapter. Do you have multiple of that model?

    Regards,

    Zack