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UB6054G-AF5-R Datasheet(PDF) 9 Page - Unisonic Technologies |
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UB6054G-AF5-R Datasheet(HTML) 9 Page - Unisonic Technologies |
9 / 13 page UB6054 Preliminary CMOS IC UNISONICTECHNOLOGIESCO.,LTD 9 of 13 www.unisonic.com.tw QW-R52-867.a APPLICATION INFORMATION(Cont.) Thermal Considerations Because of the small size of the ThinSOT package, it is very important to use a good thermal PC board layout to maximize the available charge current. The thermal path for the heat generated by the IC is from the die to the copper lead frame, through the package leads, (especially the ground lead) to the PC board copper. The PC board copper is the heat sink. The footprint copper pads should be as wide as possible and expand out to larger copper areas to spread and dissipate the heat to the surrounding ambient. Feed-through vias to inner or backside copper layers are also useful in improving the overall thermal performance of the charger. Other heat sources on the board, not related to the charger, must also be considered when designing a PC board layout because they will affect overall temperature rise and the maximum charge current. The following table lists thermal resistance for several different board sizes and copper areas. All measurements were taken in still air on 3/32" FR-4 board with the device mounted on topside. Table 1 Measured Thermal Resistance on 2-Layer Board (Note 1) COPPER AREA BOARD AREA THERMAL RESISTANCE (θJA) JUNCTION-TO-AMBIENT TOPSIDE BACKSIDE 2500mm 2 2500mm 2 2500mm 2 125°C/W 1000mm 2 2500mm 2 2500mm 2 125°C/W 225mm 2 2500mm 2 2500mm 2 130°C/W 100mm 2 2500mm 2 2500mm 2 135°C/W 50mm 2 2500mm 2 2500mm 2 150°C/W Note: 1. Each layer uses one ounce copper Table 2 Measured Thermal Resistance on 4-Layer Board (Note 1) COPPER AREA (EACH SIDE) BOARD AREA THERMAL RESISTANCE (θJA) JUNCTION-TO-AMBIENT 2500mm 2 (Note 2) 2500mm 2 80°C/W Notes: 1. Top and bottom layers use two ounce copper, inner layer use one ounce copper 2. 10,000mm 2 total copper area Increasing Thermal Regulation Current Reducing the voltage drop across the internal MOSFET can significantly decrease the power dissipation in the IC. This has the effect of increasing the current delivered to the battery during thermal regulation. One method is by dissipating some of the power through an external component, such as a resistor or diode. While this application delivers more energy to the battery and reduces charge time in thermal mode, it may actually lengthen charge time in voltage mode if VCC becomes low enough to put the UTC UB6054 into dropout. Figure 2 shows how this circuit can result in dropout as RCC becomes large. This technique works best when RCC values are minimized to keep component size small and avoid dropout. Remember to choose a resistor with adequate power handling capability. Fig2. A Circuit to Maximize Thermal Mode Charge Current |
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