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LTC1730-4 Datasheet(PDF) 10 Page - Linear Technology |
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LTC1730-4 Datasheet(HTML) 10 Page - Linear Technology |
10 / 12 page LTC1730-4/LTC1730-4.2 10 sn1730 1730fs Surface mount packages rely primarily on the copper leads (pins) to conduct the heat from the package to the sur- rounding PC board copper which is acting as a heat sink. The ground pin is especially important for conducting heat as well as providing an electrical connection. Use gener- ous amounts of copper around the ground pin and also consider feedthrough vias (plated through holes) to back- side or inner copper layers to maximize power dissipation. Table 1 lists the thermal resistance for the SO-8 package. Measured values of thermal resistance for several differ- ent board sizes and copper areas are listed. All measure- ments were taken in still air on 0.062" FR-4 board with one ounce copper. Calculating Junction Temperature Example: Find the maximum junction temperature for a battery voltage of 4V (VCC will collapse to approximately VBAT in the fast charge mode), charge current of 1A and a maximum ambient temperature of 75 °C. The power dissipated by the IC is: P= (IBAT • IBAT • RDS(ON)) + (VCC • ICC) = (1A • 1A • 0.35 Ω) + (4V • 1mA) = 0.35 + 0.004 = 0.354W The SO-8 package for the LTC1730 features a special lead frame with a lower thermal resistance and higher allow- able power dissipation. The junction-to-ambient thermal resistance of this package when soldered to a PC board is approximately 80 °C/W depending on the copper area. So the junction temperature rise above ambient will be approximately: (0.354W)(80 °C/W) = 28.3°C The maximum junction temperature is equal to the maxi- mum junction temperature rise above ambient plus the maximum ambient temperature or: TJMAX = 75°C + 28.3°C = 103.3°C Table 1. SO-8 Package Thermal Resistance COPPER AREA TOTAL THERMAL RESISTANCE TOPSIDE BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 80 °C/W 1000mm2 2500mm2 2500mm2 80 °C/W 250mm2 2500mm2 2500mm2 85 °C/W *Device is mounted on topside. Output Voltage Selection (LTC1730EGN-4) The float voltage at the BAT pin can be selected by the SEL pin. Shorting the SEL pin to ground will set the float voltage to 4.1V, while connecting it to VCC sets it to 4.2V. This feature allows the charger to be used with different types of Li-Ion cells. ACPR Output Pin (LTC1730EGN-4) When the input voltage is 40mV higher than the voltage at the BAT pin, the ACPR pin is pulled low to ground to indicate that the input supply (wall adapter) is applied. After the input supply is removed, this pin becomes high impedance. An internal 80ms delay prevents the LTC1730 from turning off if the voltage at the VCC pin rings and gets too close to VBAT because of the parasitic inductance. FAULT Output Pin (LTC1730EGN-4) The FAULT pin is pulled to ground when either one of the following conditions is detected: 1. The voltage at the NTC/SHDN pin is out of the operation range. With a 10k negative temperature coefficient thermistor placed near the battery pack, this pin indi- cates that the temperature of the pack is either too cold or too hot and the charger is suspended. Once the temperature is back to the operational range, the FAULT pin becomes high impedance and the charging re- sumes. 2. The voltage at the BAT pin stays below 2.45V for 1/4 of the programmed charge time. If VBAT remains low even with 35mA of trickle charge current for 1/4 of the total APPLICATIO S I FOR ATIO |
Similar Part No. - LTC1730-4_15 |
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Similar Description - LTC1730-4_15 |
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