Datasheet LTC4121, LTC4121-4.2 (Analog Devices) - 9

LTC4121/LTC4121-4.2
PIN FUNCTIONS BAT (Pin 9):
Battery Output Pin. Battery charge current represents the average charge current using the following is delivered from this pin through the internal charge formula: current sense resistor. In low battery conditions a small V linear charge current, I PROG LOWBAT, is sourced from this pin ICHG = hPROG • to precondition the battery. Decouple the BAT pin with a RPROG low ESR 22µF ceramic capacitor to GND. where hPROG is typically 988. Keep parasitic capacitance
BATSNS (Pin 10, LTC4121-4.2 Only):
Battery Voltage on the PROG pin to a minimum. If monitoring charge cur- Sense Pin. For proper operation, this pin must always be rent via the voltage at the PROG pin add a series resistor connected physically close to the positive battery terminal. of at least 2k to isolate stray capacitance from this node.
FB (Pin 10, LTC4121 Only):
Battery Voltage Feedback
CHRG (Pin 14):
Open-drain Charge Status Output Pin. Reference Pin. The charge function operates to achieve a Typically pulled up through a resistor to a reference final float voltage of 2.4V at this pin. Battery float voltage voltage, the CHRG pin indicates the status of the battery is programmed using a resistive divider from BAT to FB charger. The pin can be pulled up to voltages as high as to FBG, and can be programmed from 3.5V up to 18V. IN when disabled, and can sink currents up to 5mA when The feedback pin input bias current, IFB, is 25nA. Using a enabled. When the battery is being charged, the CHRG resistive divider with a Thevenin equivalent resistance of pin is pulled low. When the termination timer expires or 588k compensates for input bias current error. the charge current drops below 10% of the programmed
FBG (Pin 11, LTC4121 Only):
Feedback Ground Pin. This value, the CHRG pin is forced to a high impedance state. pin disconnects the external FB divider load from the battery
FAULT (Pin 15):
Open-drain Fault Status Output Pin. Typi- when it is not needed. When sensing the battery voltage cally pulled up through a resistor to a reference voltage, this pin presents a low resistance, RFBG, to GND. When in this status pin indicates fault conditions during a charge disabled or shutdown modes this pin is high impedance. cycle. The pin can be pulled up to voltages as high as IN
NTC (Pin 12):
Input to the Negative Temperature Coefficient when disabled, and can sink currents up to 5mA when Thermistor Monitoring Circuit. The NTC pin connects to enabled. An NTC temperature fault causes this pin to be a negative temperature coefficient thermistor which is pulled low. A bad battery fault also causes this pin to typically co-packaged with the battery to determine if the be pulled low. If no fault conditions exist, the FAULT pin battery is too hot or too cold to charge. If the battery’s remains high impedance. temperature is out of range, the LTC4121 enters STANDBY
RUN (Pin 16):
Run Pin. When RUN is pulled below VEN mode and charging is paused until the battery tempera- and its hysteresis, the device is disabled. In disabled ture re-enters the valid range. A low drift bias resistor is mode, battery charge current is zero and the CHRG and required from INTVCC to NTC and a thermistor is required FAULT pins assume high impedance states. If the voltage from NTC to GND. Tie the NTC pin to GND, and omit the at RUN is pulled below VSD, the device is in SHUTDOWN NTC resistive divider to disable NTC qualified charging if mode. When the voltage at the RUN pin rises above VEN, NTC functionality is not required. the INTVCC LDO turns on. When the INTVCC LDO rises
PROG (Pin 13):
Charge Current Program and Charge above its UVLO threshold the charger is enabled. The Current Monitor Pin. Connect a 1% resistor between RUN pin should be tied to a resistive divider from VIN to 3.01k (400mA) and 24.3k (50mA) from PROG to ground program the input voltage at which charging is enabled. to program the charge current. While in constant-current Do not float the RUN pin. mode, this pin regulates to 1.227V. The voltage at this pin 4121fc For more information www.linear.com/LTC4121 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Applications Examples Package Description Typical Application Related Parts