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LTC4059 Datasheet(PDF) 7 Page - Linear Technology |
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LTC4059 Datasheet(HTML) 7 Page - Linear Technology |
7 / 12 page LTC4059/LTC4059A 7 4059fa OPERATIO The LTC4059/LTC4059A are linear battery chargers de- signed primarily for charging single cell lithium-ion bat- teries. Featuring an internal P-channel power MOSFET, the chargers use a constant-current/constant-voltage charge algorithm with programmable current. Charge current can be programmed up to 900mA with a final float voltage accuracy of ±0.6%. No blocking diode or external sense resistor is required; thus, the basic charger circuit requires only two external components. The ACPR pin (LTC4059A) monitors the status of the input voltage with an open-drain output. The Li CC pin (LTC4059) disables constant-voltage operation and turns the LTC4059 into a precision current source capable of charging Nickel chem- istry batteries. Furthermore, the LTC4059/LTC4059A are designed to operate from a USB power source. An internal thermal limit reduces the programmed charge current if the die temperature attempts to rise above a preset value of approximately 115 °C. This feature protects the LTC4059/LTC4059A from excessive temperature, and allows the user to push the limits of the power handling capability of a given circuit board without risk of damaging the LTC4059/LTC4059A or external components. Another benefit of the thermal limit is that charge current can be set according to typical, not worst-case, ambient tempera- tures for a given application with the assurance that the charger will automatically reduce the current in worst- case conditions. The charge cycle begins when the voltage at the VCC pin rises approximately 150mV above the BAT pin voltage, a program resistor is connected from the PROG pin to ground, and the EN pin is pulled below the shutdown threshold (typically 0.85V). If the BAT pin voltage is below 4.2V, or the Li CC pin is pulled above VLi CC (LTC4059 only), the LTC4059 will charge the battery with the programmed current. This is constant-current mode. When the BAT pin approaches the final float voltage (4.2V), the LTC4059 enters constant- voltage mode and the charge current begins to decrease. To terminate the charge cycle the EN should be pulled above the shutdown threshold. Alternatively, reducing the input voltage below the BAT pin voltage will also terminate the charge cycle. APPLICATIO S I FOR ATIO Programming Charge Current The charge current is programmed using a single resistor from the PROG pin to ground. The battery charge current is 1000 times the current out of the PROG pin. The program resistor and the charge current are calculated using the following equations: R V I I V R PROG CHG CHG PROG == 1000 121 1000 121 • . ,• . For best stability over temperature and time, 1% metal- film resistors are recommended. The charge current out of the BAT pin can be determined at any time by monitoring the PROG pin voltage and using the following equation: I V R BAT PROG PROG = • 1000 Undervoltage Lockout (UVLO) An internal undervoltage lockout circuit monitors the input voltage and keeps the charger in undervoltage lockout until VCC rises approximately 150mV above the BAT pin voltage. The UVLO circuit has a built-in hysteresis of 115mV. If the BAT pin voltage is below approximately 2.75V, then the charger will remain in undervoltage lockout until VCC rises above approximately 3V. During undervoltage lockout conditions, maximum battery drain current is 4 µA. Power Supply Status Indicator (ACPR, LTC4059A Only) The power supply status output has two states: pull-down and high impedance. The pull-down state indicates that VCC is above the undervoltage lockout threshold (see Undervoltage Lockout). When this condition is not met, the ACPR pin is high impedance indicating that the LTC4059A is unable to charge the battery. |
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