Datasheet LT3652 (Analog Devices) - 8

LT3652
PIN FUNCTIONS NTC (Pin 8):
Battery Temperature Monitor Pin. This pin is charge current. The maximum charge current (ICHG(MAX)) the input to the NTC (Negative Temperature Coefficient) corresponds to 100mV across the sense resistor. This thermistor temperature monitoring circuit. This function is resistor can be set to program maximum charge cur- enabled by connecting a 10kΩ, B = 3380 NTC thermistor rent as high as 2A. The sense resistor value fol ows the from the NTC pin to ground. The pin sources 50µA, and relation: monitors the voltage across the 10kΩ thermistor. When R the voltage on this pin is above 1.36 (T < 0°C) or below SENSE = 0.1/ICHG(MAX) (Ω) 0.29V (T > 40°C), charging is disabled and the CHRG and Once a charge cycle is terminated, the input bias current of FAULT pins are both pulled low. If internal timer termina- the SENSE pin is reduced to < 0.1µA, to minimize battery tion is being used, the timer is paused, suspending the discharge while the charger remains connected. charging cycle. Charging resumes when the voltage on NTC
BOOST (Pin 11):
Bootstrapped Supply Rail for Switch returns to within the 0.29V to 1.36V active region. There Drive. This pin facilitates saturation of the switch transistor. is approximately 5°C of temperature hysteresis associated Connect a 1µF or greater capacitor from the BOOST pin with each of the temperature thresholds. The temperature to the SW pin. Operating range of this pin is 0V to 8.5V, monitoring function remains enabled while the thermistor referenced to the SW pin. The voltage on the decoupling resistance to ground is less than 250k, so if this function capacitor is refreshed through a rectifying diode, with is not desired, leave the NTC pin unconnected. the anode connected to either the battery output voltage
BAT (Pin 9):
Charger Output Monitor Pin. Connect a or an external source, and the cathode connected to the 10µF decoupling capacitance (CBAT) to ground. Depend- BOOST pin. ing on application requirements, larger value decoupling
SW (Pin 12):
Switch Output Pin. This pin is the output capacitors may be required. The charge function operates of the charger switch, and corresponds to the emitter of to achieve the programmed output battery float voltage the switch transistor. When enabled, the switch shorts (VBAT(FLT)) at this pin. This pin is also the reference for the SW pin to the V the current sense voltage. Once a charge cycle is termi- IN supply. The drive circuitry for this switch is bootstrapped above the V nated, the input bias current of the BAT pin is reduced to IN supply using the BOOST supply pin, al owing saturation of the switch for < 0.1µA, to minimize battery discharge while the charger maximum efficiency. The effective on-resistance of the remains connected. boosted switch is 0.175Ω.
SENSE (Pin 10):
Charge Current Sense Pin. Connect the
GND (Pin 13):
Ground Reference and Backside Exposed inductor sense resistor (RSENSE) from the SENSE pin to the Lead Frame Thermal Connection. Solder the exposed lead BAT pin. The voltage across this resistor sets the average frame to the PCB ground plane. 3652fe 8 For more information www.linear.com/LT3652 Document Outline Description Typical Application Absolute Maximum Ratings Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Package Description Typical Application Related Parts