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LP4060A Datasheet(PDF) 8 Page - Lowpower Semiconductor inc |
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LP4060A Datasheet(HTML) 8 Page - Lowpower Semiconductor inc |
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8 / 13 page  Preliminary Datasheet LP4060A LP4060A – Ver. 1.0 Datasheet Nov.-2007 Page 8 of 13 Applications Information Operation The LP4060A is a single cell lithium-ion battery charger using a constant-current/constant-voltage algorithm. It can deliver up to 800mA of charge current (using a good thermal PCB layout) with a final float voltage accuracy of ± 1%. The LP4060A includes an internal P-channel power MOSFET and thermal regulation circuitry. No blocking diode or external current sense resistor is required; thus, the basic charger circuit requires only two external components. Furthermore, the LP4060A is capable of operating from a USB power source. Normal Charge Cycle A charge cycle begins when the voltage at the VCC pin rises above the UVLO threshold level and a 1% program resistor is connected from the PROG pin to ground or when a battery is connected to the charger output. If the BAT pin is less than 2.9V, the charger enters trickle charge mode. In this mode, the LP4060A supplies approximately 1/10 the programmed charge current to bring the battery voltage up to a safe level for full current charging. (Note: The LP4060AX does not include this trickle charge feature). 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 LP4060A 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 1000 times the current out of the PROG pin. The program resistor and the charge current are calculated using the following equations: RSET=830/ISET The charge current out of the BAT pin can be determined at any time by monitoring the PROG pin voltage using the following equation: ISET = 830/ RSET Charge Termination A 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 100mV for longer than tTERM (typically 1ms), charging is terminated. The charge current is latched off and the LP4060A enters standby mode, where the input supply current drops to 200µA. When 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 termination. Once the average charge current drops below 1/10th the programmed value, the LP4060A 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 LP4060A constantly monitors the BAT pin voltage in standby mode. If this voltage drops below the 4.05V recharge threshold (VRECHRG), another charge cycle begins 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 7 shows the state diagram of a typical charge cycle. Charge Status Indicator(CHRG) The charge status output has three different states: strong pull-down(~10mA), weak pull-down (~12µA) and high impedance. The strong pull-down state indicates that the LP4060A is in a charge cycle. Once the charge cycle has terminated , the pin state is determined by undervoltage lockout conditions. A weak pull-down indicates that VCC meets the UVLO conditions and the LP4060A is ready to charge. High impedance indicates that the LP4060A is in undervoltage lockout mode: either VCC is less than 100mV above the BAT pin voltage or insufficient voltage is applied to the VCC pin. A microprocessor can be used to distinguish between these three states –this method is discussed in the Applications Information section. Charge Termination An internal thermal feedback loop reduces the programmed charge current if the die temperature |
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