Datasheet LTC4124 (Analog Devices) - 10

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OPERATION
When the voltage on the BAT pin approaches the final 120 120 charge voltage, the charger enters CV mode. The charge (% OF PROGRAMMED CHARGE VOL current begins to drop and a 3-hour charge termination 100 100 timer starts. The charge current continues to drop while BA 80 80 T the BAT pin voltage is maintained at the proper charge TER Y VOL voltage. Both CC and CV charging are indicated by a slow 60 60 blink (0.8Hz) at the CHRG pin. TAGE CHARGE CURRENT 40 40 In CV mode, when the charging current drops to 10% T of the full programmed charge current, the CHRG pin 20 20 AGE) CHARGE CURRENT stops blinking and assumes a pull-down state, but charg- (% OF PROGRAMMED CHARGE CURRENT) BATTERY VOLTAGE 0 0 ing continues at a continuously decreasing low charge 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 TIME (HOURS) current level. After the 3-hour charge termination time 4124 F04 expires, charging stops completely. To start a new charge
Figure 4. Typical Charging Cycle at 0.5C Rate
cycle, remove the power source at ACIN or DCIN and
vs Time with Pre-Charge Enabled
reapply it. 100
Automatic Recharge
90 After charging has terminated and while still on the char- 80 ger, the LTC4124 draws only 3.5µA from the battery. If 70 it remains in this state for a long time (days for a typical 60 battery with capacity ≥ 10mAh), the battery voltage will 50 eventually drop enough due to this 3.5µA current and 40 CHARGE CURRENT due to its own self-discharge to fall below the recharge 30 threshold (V 20 BAT_RECHG). 10 (% OF PROGRAMMED CHARGE CURRENT) To ensure that the battery is always topped off, a new 050 60 70 80 90 100 110 charge cycle automatically begins when the battery volt- BATTERY VOLTAGE (% OF FINAL CHARGE VOLTAGE) age falls below V 4124 F05 BAT_RECHG (typically 97.6% of the pro- grammed charge voltage). In the event that the 3-hour
Figure 5. Typical Charge Current vs Battery Voltage
safety timer is still running when the battery voltage falls
in a Charging Cycle with Pre-Charge Enabled
below VBAT_RECHG, the timer resets back to zero. Note that tying the PRECHG pin to GND disables the
Trickle Charging – PRECHG Pin
LTC4124 trickle charge feature. When disabled, full charge current is delivered to the battery in CC mode, Some battery manufacturers recommend low current resulting in the typical charge cycle as shown in Figure 2 pre-charging (trickle charge) for batteries that have been and Figure 3. deeply discharged. Tying the PRECHG pin to VCC enables the LTC4124 trickle charge feature.
Bad Battery Fault
When enabled, the trickle charge feature reduces the deliv- If during any charging cycle, the battery voltage stays ered charge current in CC mode to 10% of the full pro- below the pre-charge V grammed charge current if the battery voltage is below the BAT_TRKL for longer than the bad battery detection time (t pre-charge battery voltage threshold (V BB), the battery is deemed faulty BAT_TRKL is 68% of and the CHRG pin indicates this bad battery fault condition programmed charge voltage). Figure 4 and Figure 5 show by blinking fast (6Hz). a typical charging cycle with pre-charge enabled. Rev. A 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts