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LTC4050 Datasheet(PDF) 10 Page - Linear Integrated Systems |
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LTC4050 Datasheet(HTML) 10 Page - Linear Integrated Systems |
10 / 18 page LTC4065L/ LTC4065LX/LTC4065L-4.1 10 4065lfb OPERATION Undervoltage Lockout (UVLO) An internal undervoltage lockout circuit monitors the input voltage and keeps the charger in undervoltage lockout until VCC rises above 3.6V and approximately 80mV above the BAT pin voltage. The 3.6V UVLO circuit has a built-in hys- teresis of approximately 0.6V and the automatic shutdown threshold has a built-in hysteresis of approximately 50mV. During undervoltage lockout conditions, maximum battery drain current is 4μA and maximum supply current is 11μA. Shutdown Mode The LTC4065L can be disabled by pulling the EN pin above the shutdown threshold (approximately 0.82V). In shutdown mode, the battery drain current is reduced to less than 1μA and the supply current to about 20μA. Timer and Recharge The LTC4065L has an internal termination timer that starts when an input voltage greater than the undervolt- age lockout threshold is applied to VCC, or when leaving shutdown the battery voltage is less than the recharge threshold. At power-up or when exiting shutdown, if the battery volt- age is less than the recharge threshold, the charge time is set to 4.5 hours. If the battery voltage is greater than the recharge threshold at power-up or when exiting shutdown, the timer will not start and charging is prevented since the battery is at or near full capacity. Once the charge cycle terminates, the LTC4065L continu- ously monitors the BAT pin voltage using a comparator with a 2ms filter time. When the average battery voltage falls 100mV below the float voltage (which corresponds to 80% to 90% battery capacity), a new charge cycle is initiated and a 2.25 hour timer begins. This ensures that the battery is kept at, or near, a fully charged condition and eliminates the need for periodic charge cycle initiations. The CHRG output assumes a strong pull-down state during recharge cycles until C/10 is reached when it transitions to a high impendance state. Trickle Charge and Defective Battery Detection At the beginning of a charge cycle, if the battery voltage is low (below 2.9V), the charger goes into trickle charge, reducing the charge current to 10% of the full-scale cur- rent (Note: The LTC4065LX has full charge current at low-battery voltage). If the low-battery voltage persists for one quarter of the total time (1.125 hour), the battery is assumed to be defective, the charge cycle is terminated and the CHRG pin output pulses at a frequency of 2Hz with a 75% duty cycle. If for any reason the battery voltage rises above 2.9V, the charge cycle will be restarted. To restart the charge cycle (i.e., when the defective battery is replaced with a discharged battery), simply remove the input voltage and reapply it or temporarily pull the EN pin above the shutdown threshold. CHRG Status Output Pin The charge status indicator pin has three states: pull- down, pulse at 2Hz (see Trickle Charge and Defective Battery Detection) and high impedance. The pull-down state indicates that the LTC4065L is in a charge cycle. A high impedance state indicates that the charge current has dropped below 10% of the full-scale current or the LTC4065L is disabled. Figure 2 shows the CHRG status under various conditions. |
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