Datasheet LT3650-8.2, LT3650-8.4 (Analog Devices) - 7

LT3650-8.2/LT3650-8.4
pin FuncTions
charge current) is the desired soft-start interval (tSS). the BAT pin falls 2.5% below this float voltage. Once the For no RRNG/SS, this capacitor value follows the relation: charge cycle is terminated, the input bias current of the BAT C pin is reduced to <0.1µA, to minimize battery discharge RNG/SS = 50µA • tSS while the charger remains connected. The RNG/SS pin is pulled low during fault conditions, allowing graceful recovery from faults should soft-start
SENSE (Pin 10):
Charge Current Sense Pin. Connect the functionality be implemented. Both the soft-start capaci- more positive voltage end of the inductor sense resistor tor and the programming resistor can be implemented in (RSENSE) to the SENSE pin and the other end to the BAT parallel. All C/10 monitoring functions are disabled while pin. The voltage across this resistor sets the average V charge current. The maximum average charge current RNG/SS is below 0.1V to accommodate long soft-start intervals. (IMAX) corresponds to 100mV across the sense resistor. This resistor can be set to program maximum charge RNG/SS voltage can also be manipulated using an active currents as high as 2A. The sense resistor value follows device, employing a pull-down transistor to disable charge the relation: current or to dynamically servo maximum charge current. 0.1V Manipulation of the RNG/SS pin with active devices that RSENSE = have low impedance pull-up capability is not allowed (see IMAX the Applications Information section). Once the charge cycle is terminated, the input bias cur-
NTC (Pin 8):
Battery Temperature Monitor Pin. This pin is rent of the SENSE pin is reduced to <0.1µA, to minimize the input to the NTC (Negative Temperature Coefficient) battery discharge while the charger remains connected. thermistor temperature monitoring circuit. This function is
BOOST (Pin 11):
Bootstrapped Supply Rail for Switch enabled by connecting a 10kΩ, B = 3380 NTC thermistor Drive. This pin facilitates saturation of the switch transistor. from the NTC pin to ground. The pin sources 50µA, and Connect a 1µF or greater capacitor from the BOOST pin monitors the voltage across the 10kΩ thermistor. When to the SW pin. Operating range of this pin is 0V to 8.5V, the voltage on this pin is above 1.36V (T < 0°C) or below referenced to the SW pin. The voltage on the decoupling 0.29V (T > 40°C), charging is disabled and the CHRG and capacitor is refreshed through a rectifying diode, with FAULT pins are both pulled low. If internal timer termina- the anode connected to either the battery output voltage tion is being used, the timer is paused, suspending the or an external source, and the cathode connected to the charging cycle. Charging resumes when the voltage on BOOST pin. NTC returns to within the 0.29V to 1.36V active region. There is approximately 5°C of temperature hysteresis
SW (Pin 12):
Switch Output Pin. This pin is the output associated with each of the temperature thresholds. The of the charger switch, and corresponds to the emitter of temperature monitoring function remains enabled while the switch transistor. When enabled, the switch shorts thermistor resistance to ground is less than 250kΩ, so if the SW pin to the VIN supply. The drive circuitry for this this function is not desired, leave the NTC pin unconnected. switch is bootstrapped above the VIN supply using the BOOST supply pin, allowing saturation of the switch for
BAT (Pin 9):
Battery Voltage Monitor Pin. Connect 10µF maximum efficiency. The effective on-resistance of the decoupling capacitance (CBAT) from this pin to ground. boosted switch is 0.175Ω. Depending on application requirements, larger value de- coupling capacitors may be required (see the Application
SGND (Pin 13):
Ground Reference and Backside Exposed Information section). The charge function operates to Lead Frame Thermal Connection. Solder the exposed lead achieve the final float voltage at this pin. The auto-restart frame to the PCB ground plane. feature initiates a new charging cycle when the voltage at 36508284fd 7 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 Package Description Revision History Typical Application Related Parts