DESCRIPTION

The LTC4006 is a complete constant-current/constantvoltage charger controller for 2-, 3- or 4-cell lithium batteries in a small package using few external components. The PWM controller is a synchronous, quasi-constant frequency, constant off-time architecture that will not generate audible noise even when using ceramic capacitors. The LTC4006 is available in 8.4V, 12.6V and 16.8V versions with ±0.8% voltage accuracy. Charging current is programmable with a single sense resistor to ±4% typical accuracy. Charging current can be monitored as a representative voltage at the IMON pin. A timer, programmed by an external resistor, sets the total charge time or is reset to 25% of total charge time after C/10 charging current is reached. Charging automatically resumes when the cell voltage falls below 3.9V/cell. Fully discharged cells are automatically trickle charged at 10% of the programmed current until the cell voltage exceeds 2.5V/cell. Charging terminates if the low-battery condition persists for more than 25% of the total charge time. The LTC4006 includes a thermistor sensor input that suspends charging if an unsafe temperature condition is detected and automatically resumes charging when the battery temperature returns to within safe limits.

 

FEATURES

Complete Charger Controller for 2-, 3- or 4-Cell Lithium-Ion Batteries

High Conversion Efficiency: Up to 96%

Output Currents Exceeding 4A

±0.8% Accurate Preset Voltages: 8.4V, 12.6V, 16.8V

Built-In Charge Termination with Automatic Restart

AC Adapter Current Limiting Maximizes Charge Rate*

Automatic Conditioning of Deeply Discharged Batteries

Thermistor Input for Temperature Qualified Charging

Wide Input Voltage Range: 6V to 28V

0.5V Dropout Voltage; Maximum Duty Cycle: 98%

Programmable Charge Current: ±4% Accuracy

Indicator Outputs for Charging, C/10 Current Detection and AC Adapter Present

Charging Current Monitor Output

16-Pin Narrow SSOP Package

 

APPLICATIONS

Notebook Computers

Portable Instruments

Battery-Backup Systems

Standalone Li-Ion Chargers

 

OPERATION

Overview

The LTC4006 is a synchronous current mode PWM stepdown (buck) switcher battery charger controller. The charge current is programmed by the sense resistor (RSENSE) between the CSP and BAT pins. The final float voltage is internally programmed to 8.4V (LTC4006-6), 12.6V (LTC4006-2) or 16.8V (LTC4006-4) with better than ±0.8% accuracy. Charging begins when the potential at the DCIN pin rises above the voltage at CLN (and the UVLO voltage) and the ACP/SHDN pin is allowed to go high; the CHG pin is set low. At the beginning of the charge cycle, if the cell voltage is below 2.5V, the charger will trickle charge the battery with 10% of the maximum programmed current. If the cell voltage stays below 2.5V for 25% of the total charge time, the charge sequence will be terminated immediately and the CHG pin will be set to a high impedance. An external thermistor network is sampled at regular intervals. If the thermistor value exceeds design limits, charging is suspended. If the thermistor value returns to an acceptable value, charging resumes. An external resistor on the RT pin sets the total charge time. The timer can be defeated by forcing the CHG pin to a low voltage. As the battery approaches the final float voltage, the charge current will begin to decrease. When the current drops to 10% of the programmed charge current, an internal C/10 comparator will indicate this condition by sinking 25µA at the CHG pin. The charge timer is also reset to 25% of the total charge time. If this condition is caused by an input current limit condition, described below, then the C/10 comparator will be inhibited. When a time-out occurs, charging is terminated immediately and the CHG pin changes to a high impedance. The charger will automatically restart if the cell voltage is less than 3.9V. To restart the charge cycle manually, simply remove the input voltage and reapply it, or force the ACP/SHDN pin low momentarily. When the input voltage is not present, the charger goes into a sleep mode, dropping battery current drain to 15µA. This greatly reduces the current drain on the battery and increases the standby time. The charger can be inhibited at any time by forcing the ACP/SHDN pin to a low voltage.