Datasheet LT3651-8.2, LT3651-8.4 (Analog Devices) - 7

LT3651-8.2/LT3651-8.4
PIN FUNCTIONS NTC (Pin 1):
Battery Temperature Monitor Pin. This
GND (Pins 6, 23, 31, 37):
Ground. These pins are the pin is used to monitor battery temperature. Typically a ground pins for the part. Pins 31 and 37 must be connected 10kΩ NTC (negative temperature coefficient) thermistor together. Pins 6 and 23 are connected via the leadframe to (B = 3380) is embedded with the battery and connected the exposed backside Pin 37. Solder the exposed backside from the NTC pin to ground. The pin sources 50µA into to the PCB for good thermal and electrical connection. the resistor and monitors the voltage across the therm-
SW (Pins 7, 11-18, 22, 38):
Switch Output Pin. These istor, regulating charging based on the voltage. If this pins are the output of the charger switches. An inductor is function is not desired, leave the NTC pin unconnected. connected between these pins and the SENSE pin. When
ACPR (Pin 2):
Open-Collector AC Present Status Pin. the switcher is active, the inductor is charged by the high This pin sinks current to indicate that VIN is valid and the side switch from VIN and discharged by the bottom side charger is on. Typically a resistor pull-up is used on this switch to GND. Solder the exposed backside, Pin 38, to pin. This pin can be pulled up to voltages as high as VIN the PCB for good thermal connection. when disabled, and can sink currents up to 10mA when
NC (Pins 8-10,19-21):
No Connect. These pins can be left enabled. floating (not connected).
BAT (Pin 3):
Battery Voltage Monitor Pin. This pin moni-
TIMER (Pin 24):
End-Of-Cycle Timer Programming Pin. tors battery voltage. A Kelvin connection is made to the A capacitor on this pin to ground determines the full battery from this pin and a decoupling capacitor (CBAT) charge end-of-cycle time. Full charge end-of-cycle time is is placed from this pin to ground. programmed with this capacitor. A 3 hour charge cycle is The charge function operates to achieve the final float obtained with a 0.68µF capacitor. This timer also controls voltage at this pin. The auto-restart feature initiates a new the bad battery fault that is generated if the battery does not charging cycle when the voltage at the BAT pin falls 2.5% reach the precondition threshold voltage within one-eighth below this float voltage. Once the charge cycle is termi- of a full cycle (22.5 minutes for a 3 hour charge cycle). nated, the input bias current of the BAT pin is reduced to The timer based termination is disabled by connecting the <0.1µA to minimize battery discharge while the charger TIMER pin to ground. With the timer function disabled, remains connected. charging terminates when the charge current drops below a
SENSE (Pin 4):
Charge Current Sense Pin. The charge C/10 rate, or approximately 10% of maximum charge rate. current is monitored with a sense resistor (RSENSE) con-
FAULT (Pin 25):
Open-Collector Fault Status Output. This nected between this pin and the BAT pin. The inductor pin indicates charge cycle fault conditions during a battery current flows through RSENSE to the battery. The voltage charging cycle. Typically a resistor pull-up is used on this across this resistor sets the average charge current. The pin. This status pin can be pulled up to voltages as high maximum average charge current (IMAX) corresponds to as V 95mV across the sense resistor. IN when disabled, and can sink currents up to 10mA when enabled. A temperature fault causes this pin to be
BOOST (Pin 5):
Bootstrapped Supply Rail for Switch pulled low. If the internal timer is used for termination, Drive. This pin facilitates saturation of the high side switch a bad battery fault also causes this pin to be pulled low. transistor. Connect a 1µF or greater capacitor from the If no fault conditions exist, the FAULT pin remains high BOOST pin to the SW pin. The operating range of this pin impedance. is 0V to 8.5V, referenced to the SW pin when the switch is
CHRG (Pin 26):
Open-Collector Charger Status Output. high. The voltage on the decoupling capacitor is refreshed This pin indicates the battery charging status. Typically through a rectifying diode, with the anode connected to a resistor pull-up is used on this pin. This status pin can either the battery output voltage or an external source, be pulled up to voltages as high as V and the cathode connected to the BOOST pin. IN when disabled, 36518284fa For more information www.linear.com/LT3651-8.2 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 Typical Application Related Parts