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LTC4061-4.4 Datasheet(PDF) 9 Page - Linear Technology |
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LTC4061-4.4 Datasheet(HTML) 9 Page - Linear Technology |
9 / 20 page LTC4061-4.4 9 406144fb The LTC4061-4.4 is designed to charge single-cell lithium-ion batteries. Using the constant current/constant voltage algorithm, the charger can deliver up to 1A of chargecurrentwithafinalfloatvoltageaccuracyof±0.4%. The LTC4061-4.4 includes an internal P-channel power MOSFET and thermal regulation circuitry. No blocking diode or external sense resistor is required; thus, the basic charger circuit requires only two external components. Normal Operation The charge cycle begins when the voltage at the VCC pin rises above the UVLO level and a discharged battery is connected to BAT. If the BAT pin voltage is below 2.9V, the charger enters trickle charge mode. In this mode, the LTC4061-4.4 supplies 1/10th of the programmed charge current in order to bring the battery voltage up to a safe level for full current charging. Once the BAT pin voltage rises above 2.9V, the charger enters constant current mode, where the programmed charge current is supplied to the battery. When the BAT pin approaches the final float voltage (4.375V), the LTC4061-4.4entersconstantvoltagemodeandthecharge current decreases as the battery becomes fully charged. The LTC4061-4.4 offers several methods with which to terminate a charge cycle. Connecting an external capaci- tor to the TIMER pin activates an internal timer that stops the charge cycle after the programmed time period has elapsed. Grounding the TIMER pin and connecting a resis- tor to the IDET pin causes the charge cycle to terminate once the charge current falls below a set threshold when the charger is in constant voltage mode. Connecting the TIMER pin to VCC disables internal termination, allowing external user charge termination through the EN input. See Applications Information for more information on charge termination methods. Programming Charge Current The charge current is programmed using a single resistor from the PROG pin to ground. When the charger is in the constant current mode, the voltage on the PROG pin is 1V. The battery charge current is 1000 times the current out of the PROG pin. The program resistor and the charge current are calculated by the following equations: R V I I V R PROG CHG CHG PROG = = 1000 1000 , The charge current out of the BAT pin can be determined at any time by monitoring the PROG pin voltage and applying the following equation: I V R BAT PROG PROG = •1000 SmartStart When the LTC4061-4.4 is initially powered on or brought out of shutdown mode, the charger checks the battery voltage. If the BAT pin is below the recharge threshold of 4.275V (which corresponds to approximately 80-90% battery capacity), the LTC4061-4.4 enters charge mode and begins a full charge cycle. If the BAT pin is above 4.275V, the LTC4061-4.4 enters standby mode and does not begin charging. This feature reduces the number of unnecessary charge cycles, prolonging battery life. Automatic Recharge When the charger is in standby mode, the LTC4061-4.4 continuously monitors the voltage on the BAT pin. When the BAT pin voltage drops below 4.275V, the charge cycle is automatically restarted and the internal timer is reset to 50% of the programmed charge time (if time termina- tion is being used). This feature eliminates the need for periodicchargecycleinitiationsandensuresthatthebattery is always fully charged. Automatic recharge is disabled in user termination mode. Thermal Regulation Aninternalthermalfeedbackloopreducestheprogrammed charge current if the die temperature attempts to rise above a preset value of approximately 105°C. This feature protectstheLTC4061-4.4fromexcessivetemperatureand allows the user to push the limits of the power handling capability of a given circuit board without risk of damaging the LTC4061-4.4. The charge current can be set according to typical (not worst-case) ambient temperatures with the assurance that the charger will automatically reduce the current in worst-case conditions. OPERATIO |
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