18650 li ion rechargeable battery

　　Extend 18650 li ion rechargeable batterylife technology using low threshold voltage

　　For years, semiconductor manufacturers in the power management business struggled to keep up with the needs of end system users. Portable electronics are increasingly being renovated in functionality and require peak performance, requiring designers to achieve the highest possible efficiency within the physical dimensions of the device. Although the 18650 li ion rechargeable batteryindustry has worked hard to develop alternative 18650 li ion rechargeable batterytechnologies with higher capacity than traditional nickel-cadmium (NiCd) batteries, they are still far from meeting the energy needs of the new generation of portable devices. Therefore, portable applications have to seek innovative developments in low-power circuit design so that design engineers can allow the end system to use 18650 li ion rechargeable batteryresources with the highest possible efficiency. In portable devices, components make up a major portion of the power budget, and it's clear that to keep up with changing demands, semiconductor device manufacturers will need to continue to innovate to help reduce the power consumption of portable products.

　　Taking mobile phones as an example, reducing the operating voltage of major components in handheld devices such as analog and digital baseband chips is one of the ways to reduce power consumption. When the maximum performance of the DSP or microprocessor is not required, the core supply voltage can be reduced and the clock frequency can be reduced. More and more new generation low-power applications adopt this technology to save system energy as much as possible. The formula pC~(VC)2.F describes the power consumption of a DSp core. Here, pC is the power consumption of the core, VC is the core voltage, and F is the core clock frequency. Lowering the internal clock frequency can reduce power consumption, and lowering the core supply voltage can reduce power consumption even more.

　　What role can advanced silicon and packaging technologies play?

　　There are many design factors for the performance of speakers in emerging power-hungry portable devices. This article will focus on the power MOSFET, the most common power switch in low-voltage applications, as an example to illustrate the impact of the latest silicon technology breakthroughs in increasing power requirements. To illustrate the impact of these technological advances, it is necessary to understand some key parameters of power MOSFETs.

　　The on-resistance (rDS(on)) of the channel is controlled by the transverse and longitudinal electric fields of the channel. The channel resistance is mainly determined by the gate-source voltage difference. When VGS exceeds the threshold voltage (VGS(th)), the FET starts to conduct. Many operations require a switch ground point. The resistance of a power MOSFET channel is related to the physical dimensions determined by the formula R=L/A, where r is the resistivity, L is the channel length, and A is WxT, the cross-sectional area of the channel.

　　In a usual FET structure, L and W are determined by the device geometry, while the channel thickness T is the distance between the two depletion layers. The position of the depletion layer changes with the gate-source bias voltage or the drain-source voltage. The position of the depletion layer changes with the gate-source bias voltage or the drain-source voltage. When T decreases to zero under the influence of VGS and VDS, the two opposite depletion layers will be connected together, and the increased channel resistance (rDS(on)) will approach infinity.

　　Figure 1 is the relationship curve between rDS(on) and VGS characteristics. Region 1 corresponds to the situation where the accumulated charge is insufficient to produce reverse direction. The condition corresponding to Region 2 is that there is enough charge to reverse part of the p-region and form a channel, but this is not enough because the "space charge" effect is also important. Region 3 corresponds to the case of limited charge. When the gate potential increases, rDS(on) does not change significantly.

　　:Relationship curve between rDS(on) and VGS characteristics

　　Threshold voltage (VGS(th)) is a parameter used to describe how much voltage is required to turn on the channel. VGS controls the size of the saturation current ID. An increase in VGS will make the constant ID smaller, so a smaller VDS is needed to reach the inflection point of the curve (shown in Figure 2).

　　(Text in the picture: At rated RDS(on) and 1.5V voltage, the driver circuit can turn on the MOSFET without the need for a level conversion circuit)

　　The relationship curve between rDS(on) and Id under different gate voltages (data source: VishaySiliconix)

　　High-speed performance and low-power operation can be achieved by using transistors with low threshold voltages. By using low-threshold power MOSFETs in the signal path, the supply voltage (VDD) can be reduced, thereby reducing switching power dissipation without affecting performance. This is why, in order to meet the increasing needs of users to reduce power consumption and extend 18650 li ion rechargeable batterylife, many ASICs used in portable electronic systems operate with a core voltage of around 1.5V. However, until now, due to the lack of power MSOFETs that can conduct at such a low voltage, designers have been unable to take advantage of voltages below 1.8V in reducing power consumption without using level conversion circuits. Conversion circuitry makes the circuit more complex and also increases power consumption. VishaySiliconix was the first in the industry to launch a series of breakthrough power MOSFETs that can guarantee conduction at a voltage of 1.5V, thereby solving this problem.

　　Reducing VGS(th) allows the driver to turn on the switch with a lower output voltage, reducing the level shifting circuitry required

　　From past experience, we need a threshold voltage of no less than 1.8V to compensate for the negative temperature coefficient of the threshold point in all power MSOFEs. If the device is operated at a temperature of 125°C (which is likely to be the case in portable applications), existing MOSFET designs have to increase the MOSFET threshold voltage to prevent the MOSFET from self-conduction, because even if the applied VGS is 0V , MOSFETs with low threshold voltages may also self-conduct.

　　Especially portable devices and mobile phones have endless demands for multimedia capabilities. Designers must strive to provide greater data processing capabilities while trying to meet the special power requirements of next-generation portable devices. But there is no doubt that power MOSFETs using advanced silicon wafer technology and packaging technology will be able to provide the power efficiency, ultra-small size and low cost expected by designers, turning these multimedia mobile phones from ideas into reality.

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