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LTC4057ES5-4.2 Datasheet(PDF) 9 Page - Linear Technology |
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LTC4057ES5-4.2 Datasheet(HTML) 9 Page - Linear Technology |
9 / 12 page LTC4057-4.2 9 4057f Figure 2. A Circuit to Maximize Thermal Mode Charge Current VCC RPROG RCC Li-Ion CELL 405742 F02 LTC4057-4.2 1 µF VS BAT PROG GND + 4 3 5 2 Solving for IBAT using the quadratic formula1. I VV VV RC T R BAT S BAT S BAT CC A JA CC = ° (– ) – (– ) (– ) 2 4 120 2 θ Using RCC = 0.25Ω, VS = 5V, VBAT = 3.75V, TA = 25°C and θJA = 125°C/W, we can calculate the thermally regulated charge current to be: IBAT = 708.4mA Note 1: Large values of RCC will result in no solution for IBAT. This indicates that the LTC4057 will not generate enough heat to require thermal regulation. 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 LTC4057 into dropout. Figure 3 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. Remem- ber to choose a resistor with adequate power handling capability. RCC (Ω) 0 1000 800 600 400 200 0 0.5 1.0 1.25 405442 F03 0.25 0.75 1.5 1.75 CONSTANT CURRENT VBAT = 3.75V TA = 25°C θJA = 125°C/W RPROG = 1.25kΩ THERMAL MODE DROPOUT VS = 5.25V VS = 5.5V VS = 5V Figure 3. Charge Current vs RCC APPLICATIO S I FOR ATIO |
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