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LTC4069 Datasheet(PDF) 8 Page - Linear Technology |
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LTC4069 Datasheet(HTML) 8 Page - Linear Technology |
8 / 18 page LTC4069 8 4069fc For more information www.linear.com/LTC4069 operaTion The charge cycle begins when the voltage at the VCC pin rises above 3.5V and approximately 80mV above the BAT pin voltage, a 1% program resistor is connected from the PROGpintogroundandtheNTCpinvoltagestaysbetween 0.76 • VCC and 0.35 • VCC or below 0.016 • VCC. If the BAT pin voltage is below 2.9V, the charger goes into trickle charge mode, charging the battery at one-tenth the programmed charge current to bring the cell voltage up to a safe level for charging. If the BAT pin voltage is above 4.1V, the charger will not charge the battery as the cell is near full capacity. Otherwise, the charger goes into the fast charge constant-current mode. When the BAT pin approaches the final float voltage (4.2V), the LTC4069 enters constant-voltage mode and the charge current begins to decrease. When the current drops to 10% of the full-scale charge current, an internal comparator turns off the N-channel MOSFET on the CHRG pin and the pin assumes a high impedance state. An internal timer sets the total charge time, tTIMER (typi- cally 4.5 hours). When this time elapses, the charge cycle terminates and the CHRG pin assumes a high impedance state. The charge cycle will automatically restart if the BAT pin voltage falls below VRECHRG (typically 4.1V). To manually restart the charge cycle, remove the input voltage and reapply it, or momentarily float the PROG pin and reconnect it. Programming Charge Current The charge current is programmed using a single resistor fromthePROGpintoground.Thebatterychargecurrentis 1000 times the current out of the PROG pin. The program resistor and the charge current are calculated using the following equations: RPROG =1000• 1V ICHG , ICHG = 1000V RPROG 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: IBAT = VPROG RPROG •1000 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 hysteresis 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 LTC4069 can be disabled by floating the PROG pin. In shutdown mode, the battery drain current is reduced to less than 1µA and the supply current to about 20µA. Timer and Recharge The LTC4069 has an internal termination timer that starts whenaninputvoltagegreaterthantheundervoltagelockout threshold is applied to VCC,orwhenleavingshutdownand the battery voltage is less than the recharge threshold. Atpower-uporwhenexitingshutdown,ifthebatteryvoltage is less than the recharge threshold, the charge time is set to 4.5 hours. If the battery temperature is either too high or too low, the timer will pause until the battery returns to normal temperature. If the battery is greater than the rechargethresholdatpower-uporwhenexitingshutdown, the timer will not start and charging is prevented since the battery is at or near full capacity. Once the charge cycle terminates, the LTC4069 continu- ously monitors the BAT pin voltage using a comparator with a 2ms filter time. When the battery voltage falls |
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