Highly integrated single-chip lithium battery maintenance solution
Nowadays, lithium batteries are more and more widely used, from cell phones, MP3, MP4, GPS, toys and other portable devices to gas meters that need to continue to save data, and their market capacity has now reached several hundred million per month. In order to prevent the lithium battery in overcharge, overdischarge, overcurrent and other abnormal conditions affect the battery life, generally through the lithium battery maintenance device to prevent abnormal conditions on the battery damage.
The circuit principle of the lithium battery maintenance device is shown in Figure 1, mainly by the battery maintenance control IC and external discharge switch M1 and charging switch M2 to achieve. When the P+/P- terminal is connected to the charger and the battery is charged normally, M1 and M2 are on; when the control IC detects a charging anomaly, M2 is turned off to stop charging. When the P+/P- terminal is connected to the load and the battery is discharged normally, M1 and M2 are on; when the control IC detects the discharge anomaly, M1 will be turned off to stop the discharge.
Figure 1: Circuit principle of lithium battery maintenance device.
Several existing lithium battery maintenance plans
Figure 2 is a commonly used lithium battery maintenance board designed based on the above lithium battery maintenance principle. The SOT23-6L package in the figure is the control IC, and the SOP8 package is the dual switch tube M1, M2. Because the process of making the control IC and the process of making the switch tube are different, thus the two chips in Figure 2 are made from different processes, and generally these two chips are also provided by different chip manufacturers.
Figure 2: Traditional battery maintenance plan.
In recent years, the industry has seen a trend of packaging several chips together to improve integration and reduce the final plan area. The Li-ion battery maintenance market is no exception. The two Li-ion battery maintenance plans A and B in Figure 3 appear to integrate the two chips in Figure 2 into a single chip, but in practice, the controller IC and the switching tube chip inside the package are still separate, from different manufacturers, the plan is only the two together, commonly known as "two cores in one".
Figure 3: The "two cores in one" Li-ion battery maintenance plan.
Because the internal two chips are still from different manufacturers, the shape can not be well matched, resulting in different shapes of the final package, in many cases can not choose a universal package. This package volume is relatively large, and can not save peripheral components, so this "two cores in one" plan in practice does not save much space. In terms of cost, although the cost of two packages is reduced to the cost of a package, but because the package is generally larger, some are not universal packages, some need to use the chip stacked package in order to reduce the scale of the package, so compared with the traditional two-chip plan, its cost advantage is not significant.
Figure 4 shows a real single-chip plan that integrates the controller chip and the switching tube chip in the same wafer. The switch tube in the traditional plan schematic diagram 1 is an N-type tube, connected between B- and P- in Figure 1, commonly known as negative maintenance. The plan in Figure 4, because of technical reasons, the switching tube can only be changed to a P-type tube, connected between B+ and P+, commonly known as positive maintenance. After finishing the maintenance board plan with this chip, the user needs to replace the test equipment and concept when testing the maintenance board. Although this plan reduces the packaging cost, but the chip cost is not reduced, and there is no real cost advantage when competing with the traditional plan of large volume and sophistication. On the contrary, the concept of positive electrode maintenance, which is incompatible with the traditional plan, has become a great obstacle to its promotion.
Figure 4: Li-ion battery maintenance plan for positive electrode maintenance.
Although the above "two cores in one" plan and single chip positive maintenance plan bring certain advantages to users in terms of planning area and cost, the advantages are still not significant. These plans together with some drawbacks, so in the process of competing with the sophisticated traditional plan customers, and ultimately only to reduce the gross margin space to play price war. Because the real original cost of these plans does not have significant advantages, so with the traditional plan of control IC and switch tube chip price reduction, these "two cores in one" plan or positive maintenance plan and can not shake the traditional plan of the market control position.
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