Datasheet LT3651-8.2, LT3651-8.4 (Analog Devices) - 10

LT3651-8.2/LT3651-8.4
OPERATION Overview
2.5% from the full charge float voltage, the LT3651-8.2/ The LT3651-8.2/LT3651-8.4 are complete Li-Ion battery LT3651-8.4 engage an automatic charge cycle restart. The chargers, addressing wide input voltage and high currents IC also automatically restarts a new charge cycle after a (up to 4A). High charging efficiency is produced with a bad battery fault once the failed battery is removed and constant frequency, average current mode synchronous replaced with another battery. step-down switcher architecture. After charging is completed the input bias currents on the The charger includes the necessary circuitry to allow for pins connecting to the battery are reduced to minimize programming and control of constant current, constant battery discharge. voltage (CC/CV) charging with both current only and timer The LT3651-8.2/LT3651-8.4 contain provisions for a bat- termination. High charging efficiency is achieved by the tery temperature monitoring circuit. Battery temperature switcher by using a bootstrapped supply for low switch is monitored by using a NTC thermistor located with the drop for the high side driver and a MOSFET for the low battery. If the battery temperature moves outside a safe side (synchronous) switch. charging range of 0°C to 40°C the charging cycle suspends Maximum charge current is set with an external sense re- and signals a fault condition. sistor in series with the inductor and is adjustable through The LT3651-8.2/LT3651-8.4 contain two digital open- the RNG/SS pin. Total system input current is monitored collector outputs, which provide charger status and signal with an input sense resistor and is used to maintain con- fault conditions. These binary coded pins signal battery stant input current by regulating battery charge current. charging, standby or shutdown modes, battery temperature It is adjustable through the ILIM pin. faults and bad battery faults. If the battery voltage is low, charge current is automatically A precision undervoltage lockout is possible by using a reduced to 15% of the programmed current to provide resistor divider on the shutdown pin (SHDN). The input safe battery preconditioning. Once the battery voltage supply current is 17µA when the IC is in shutdown. climbs above the battery precondition threshold, the IC automatically increases the maximum charge current to
General Operation (See Block Diagram)
the full programmed value. The LT3651-8.2/LT3651-8.4 use an average current mode Charge termination can occur when charge current de- control loop architecture to control average charge current. creases to one-tenth the programmed maximum charge The LT3651-8.2/LT3651-8.4 sense charger output voltage current (C/10 termination). Alternately, termination can via the BAT pin. The difference between this voltage and the be time based through the use of an internal program- internal float voltage reference is integrated by the voltage mable charge cycle control timer. When using the timer error amplifier (V-EA). The amplifier output voltage (ITH) termination, charging continues beyond the C/10 level to corresponds to the desired average voltage across the “top-off” a battery. Charging typically terminates three inductor sense resistor, RSENSE, connected between the hours after initiation. When the timer-based scheme is SENSE and BAT pins. The ITH voltage is divided down by used, bad battery detection is also supported. A system a factor of 10, and provides a voltage offset on the input fault is triggered if a battery stays in precondition mode of the current error amplifier (C-EA). The difference be- for more than one-eighth of the total charge cycle time. tween this imposed voltage and the current sense resistor Once charging is terminated and the LT3651-8.2/ voltage is integrated by C-EA. The resulting voltage (VC) LT3651-8.4 are not actively charging, the IC automatically provides a voltage that is compared against an internally enters a low current standby mode in which supply bias generated ramp and generates the switch duty cycle that currents are reduced to <85µA. If the battery voltage drops controls the charger’s switches. 36518284fa 10 For more information www.linear.com/LT3651-8.2 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Typical Application Related Parts