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LTC4054L-4.2 Datasheet(PDF) 8 Page - Linear Technology |
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LTC4054L-4.2 Datasheet(HTML) 8 Page - Linear Technology |
8 / 16 page 8 LTC4054L-4.2 4054l42f OPERATIO 1Any external sources that hold the PROG pin above 100mV will prevent the LTC4054L from terminating a charge cycle. The LTC4054L is a single cell lithium-ion battery charger using a constant-current/constant-voltage algorithm. Its ability to control charge currents as low as 10mA make it well-suited for charging low capacity lithium-ion coin cell batteries. The LTC4054L includes an internal P-channel power MOSFET and thermal regulation circuitry. No block- ing diode or external sense resistor is required; thus, the basic charger circuit requires only three external compo- nents. Furthermore, the LTC4054L is capable of operating from a USB power source. Normal Charge Cycle The charge cycle begins when the voltage at the VCC pin rises above the UVLO level and a 1% program resistor is connected from the PROG pin to ground. If the BAT pin is less than 2.9V, the charger enters trickle charge mode. In this mode, the LTC4054L supplies approximately 1/10 the programmed charge current in order to bring the battery voltage up to a safe level for full current charging. When 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 (4.2V), the LTC4054L enters constant-voltage mode and the charge current begins to decrease. When the charge current drops to 1/10 of the programmed value, the charge cycle ends. Programming Charge Current The charge current is programmed using a single resistor from the PROG pin to ground. The battery charge current is 150 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 == 150 150 , The charge current out of the BAT pin can be determined at any time by monitoring the PROG pin voltage using the following equation: I V R BAT PROG PROG = • 150 Charge Termination The charge cycle is terminated when the charge current falls to 1/10th the programmed value after the final float voltage is reached. This condition is detected by using an internal, filtered comparator to monitor the PROG pin. When the PROG pin voltage falls below 100mV1 for longer than tTERM (typically 1ms), charging is terminated. The charge current is latched off and the LTC4054L enters standby mode, where the input supply current drops to 200 µA.(Note:C/10terminationisdisabledintricklecharg- ing and thermal limiting modes.) While charging, transient loads on the BAT pin can cause the PROG pin to fall below 100mV for short periods of time before the DC charge current has dropped to 1/10th the programmed value. The 1ms filter time (tTERM) on the termination comparator ensures that transient loads of this nature do not result in premature charge cycle termi- nation. Once the average charge current drops below 1/10th the programmed value for longer than tTERM , the LTC4054L terminates the charge cycle and ceases to provide any current through the BAT pin. In this state, all loads on the BAT pin must be supplied by the battery. The LTC4054L constantly monitors the BAT pin voltage in standby mode. If this voltage drops below the 4.05V recharge threshold (VRECHRG), another charge cycle be- gins and current is once again supplied to the battery. To manually restart a charge cycle when in standby mode, the input voltage must be removed and reapplied, or the charger must be shut down and restarted using the PROG pin. Figure 1 shows the state diagram of a typical charge cycle. |
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