Dynamic Power Path Management for Battery Charging ICs

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If the design of some battery products is not good, there will be a phenomenon that when the product battery is over-discharged and then charged, the battery may not be charged. The reason is generally because there is no dynamic power path management function in the charging design of such products. When the battery is exhausted and charged, the product generally turns on some functions to display charging progress information to the user. If the system power supply path and battery charging and discharging path in the product are not separated independently, the system will draw power from the battery being charged. At this time, if the battery is charged with less power, it may cause battery failure and stop charging.

Moreover, this system power supply path is not independent, which will cause the battery to charge and discharge too many times, accelerating aging. Charging chips with dynamic power path management function can perfectly solve the above two problems. The product can start up normally as long as it is connected to an external power supply. This article briefly introduces the principle of dynamic power path management (DPPM). If you want to learn more, you can find it in the datasheet of the relevant charging chip.

When an external power source is connected, the DPPM circuit starts to continuously monitor the input current and limit the input current below a certain threshold. The output voltage of the chip is used to power the system load, which is regulated to 210mV higher than the battery voltage. When the battery voltage is lower than 3.2V, the output voltage is fixedly clamped at 3.41V. This allows the system to start normally when an external power source is connected even when the battery is discharged. The current input from the external power source not only charges the battery, but also powers the system, as shown in Figure 1.

Figure 1

When an external power supply is connected, the DPMM will give priority to meeting the current demand of the system load.

The DPMM monitors the input voltage, and if the input voltage drops below a certain threshold, the input current is limited to prevent the input voltage from dropping further, as shown in Figure 2.

Figure 2

When the sum of the charging current and the system load current exceeds the maximum input current limit, the output voltage will begin to drop. When the voltage drops to a certain threshold, the chip will enter DPMM mode. In this mode, the battery charging current will decrease and the current output to the load will increase to maintain the voltage output to the system load.

If the battery charging current in this mode drops to zero, and the current output to the system load increases to exceed the maximum input current limit, the output voltage will begin to drop again. When the output voltage drops to a certain threshold, the battery will also discharge the output current to supplement the system load until the output voltage rises again to exceed a certain threshold, and the battery will stop discharging to supplement the system load. In the mode where the battery supplements the system load, the battery output current cannot be adjusted, but there will be short-circuit protection. The current waveform is shown in Figure 3, and the current flow is shown in Figure 4.

Figure 3

Figure 4

Under normal circumstances, when the battery is fully charged, the battery switch will be disconnected, and the system load will be powered by the external input power without drawing power from the battery, thereby extending the battery life, as shown in Figure 5.

Figure 5

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In rechargeable mobile devices, charging IC is an essential component