Analysis of design points and mainstream schemes o

Analysis of charging management design points and mainstream solutions

although there are many brands on the market at present, their charging circuits are roughly the same, and they all use PMOS based charging circuits. When using PMOS, it is easy to control its switch with low voltage, and the voltage on the motherboard is mostly about 3V, so it is easy to realize switch control. In addition, MOS transistor is a voltage type control device in the form of keynote + seminar + industry docking. Compared with triode, the power consumption is also much smaller

common charging circuits can be divided into the following three types:

1. Pmos+ Schottky diode: MTK and Spreadtrum platform adopt this method. PMOS controls the switch of charging and the size of charging current. Schottky diode prevents the battery from pouring back current through the internal parasitic diode of PMOS, and the forward direction is 8 Experiment span: 450mm (can be widened) when conducting, its forward voltage drop is smaller than that of ordinary diodes

recommended products: bf9024spd-m (8pin), bf9024spd-ms (6pin): please refer to table 1 for main parameters. Table 1 Bf9024spd series main parameters

Figure 2 Separating PMOS and diodes

bf9024spd-m (8pin) and bf9024spd-ms (6pin) are power devices for this application, as shown in Figure 1 when the machine starts running. In order to reduce MOS heating during long-time charging, BYD microelectronics exposed its bottom heat sink in the package for better heat dissipation. Don't underestimate this heat sink. It can not only improve the heat dissipation efficiency during charging, help improve product reliability, but also make the battery charge more fully. Because the internal resistance of MOS is a positive temperature coefficient, that is, the higher the temperature, the greater the internal resistance. At 50 ℃, the internal resistance will increase by about 5% for every 10 ℃ rise in temperature. With this heat sink, the accelerator can dissipate heat, so that the increase in internal resistance is controlled below 3%. During charging, the charging voltage of the battery can be about 50mV higher than that of similar products

when bf9024spd-m was applied on mtk6223 platform, we recorded more than 2000 data when the battery voltage was charged from 2.8V to a stable 4.185v. During the whole process, from a pre charging current of about 60mA to a constant charging current of 550mA, and then to a pulse current of about 50mA at full charge, the monitored battery voltage finally stabilized between 4.185 and 4.195. Please refer to figure 3; When charging with USB port, the battery voltage is stable at 4.188v when fully charged, please refer to figure 4. During the whole charging process, the consistency of the full charge voltage of the battery is very good, and the consistency of the whole charging curve is also very good

figure III Bf9024spd-m applied to mtk6223 platform charging curve - adapter charging

Figure 4 Bf9024spd-m is applied to the charging curve of mtk6223 platform - USB port charging

since bf9024spd-m and bf9024spd-ms are connected with the drain (d pole) of PMOS and the negative pole (k pole) of Schottky diode, it cannot be used as GND or connected with other signal lines in design. Please note that there is no grounding pad or other signal wiring at the bottom of PCB layout. For the corresponding layout, please refer to figure 5 and 6 below

figure v Bf9024spd-m layout refer to figure 6 Bf9024spd-ms layout reference

these two products have been certified by Spreadtrum platform. You can refer to the original reference design BOM of Spreadtrum

in low-cost applications, separate MOS tubes and Schottky diodes can be used to replace integrated devices, as shown in Figure 2. The small package of bf92301p can meet your design needs. Please refer to table 2 for its main parameters

2. Pmos+ PMOS: this method is adopted in Ti, some MTK platforms and dual battery platforms. This application is an improvement of pmos+ Schottky diode application. In the charging circuit of pmos+ Schottky diode application, Schottky diode will occupy a voltage drop of more than 0.4V due to continuous conduction. After replacing Schottky diode with PMOS tube, the voltage drop can be greatly reduced due to the very small conduction internal resistance of MOS, so as to ensure that the USB port or external 5V reference voltage can still be sufficiently higher than the voltage required for charging a single lithium battery after being lost in the charging circuit

recommended product: bf9024dpd-ms. please refer to table 2 for main parameters

with the motherboard becoming smaller and smaller, and more and more functions, people hope that digital products can be used after a single charge. Looking for sustainable, excellent and cheap oil substitutes has become an important topic in the polymer industry, which has attracted the high attention of governments all over the world for a longer time. Under this demand, the application of dual battery is derived. Dual PMOS can make good use of its extremely low conduction voltage drop and current single flow controllability in the application of dual batteries

3. PNP tube +pmos:qualcomm platform almost adopts this method. PNP tube is used to control the switch of charging and the size of charging current, and PMOS is used as a switching element to realize the connection and disconnection of charging circuit

recommended product: bf92301p. Please refer to table 2 for main parameters

Table II The main parameters of bf92301p and bf9024dpd-ms

with the continuous updating of the products of platform suppliers, the external circuit of pmos+ Schottky diode is always one of the most concise and reliable choices in the application of charging management. From 6600l to 6600l6, 6600l7 and 6610k of Spreadtrum, this method has been adopted as the charging design. As for the new platform mtk6253, which was vigorously promoted by MediaTek, in addition to its own power management part, it integrates overvoltage protection (OVP), constant current and other functions in its external circuit to form secondary protection. Of course, this practice also appeared in the early design of MediaTek, that is, PMIC (power management IC) is used to deal with the power supply part. However, with the maturity of the application technology, the output interface of the adapter is unified, and its output voltage (5V ± 5%) can be completely consistent with the standard USB interface. Some design companies with research and development strength have applied pmos+ Schottky diodes to the mtk6253 platform, only adding a zener diode to the external power input part, which greatly saves the cost of power management

summary of this paper

in common charging circuits, PMOS is a key device in application, and its quality and performance directly affect the charging heat and charging time. BYD microelectronics' MOS products have been tempered by the market for many years, and have been well improved in terms of product quality, price, delivery time and product technical support. (end)