Datasheet LTC4120, LTC4120-4.2 (Analog Devices) - 9

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PIN FUNCTIONS INTVCC (Pin 1):
Internal Regulator Output Pin. This pin is sense resistor. In low battery conditions a small linear the output of an internal linear regulator that generates the charge current, ILOWBAT, is sourced from this pin to pre- internal INTVCC supply from IN. It also supplies power to condition the battery. Decouple the BAT pin with a low the switch gate drivers and the low battery linear charge ESR 22µF or greater ceramic capacitor to GND. current ILOWBAT. Connect a 2.2µF low ESR capacitor from
BATSNS (Pin 10, LTC4120-4.2 Only):
Battery Voltage INTVCC to GND. Do not place any external load on INTVCC Sense Pin. For proper operation, this pin must always be other than the NTC bias network. Overloading this pin can connected physically close to the positive battery terminal. disrupt internal operation. When the RUN pin is above VEN, and INTVCC rises above the UVLO threshold, and
FB (Pin 10, LTC4120 Only):
Battery Voltage Feedback Pin. IN rises above BAT by ∆VDUVLO and its hysteresis, the The charge function operates to achieve a final float voltage charger is enabled. of 2.4V at this pin. Battery float voltage is programmed
BOOST (Pin 2):
Boosted Supply Pin. Connect a 22nF using a resistive divider from BAT to FB to FBG, and can be boost capacitor from this pin to the SW pin. programmed up to 11V. The feedback pin input bias cur- rent, IFB, is 25nA. Using a resistive divider with a Thevenin
IN (Pin 3):
Positive Input Power Supply. Decouple to GND equivalent resistance of 588k compensates for input bias with a 10µF or larger low ESR capacitor. current error (see curve of FB Pin Bias Current versus
SW (Pin 4):
Switch Pin. The SW pin delivers power from Temperature in the Typical Performance Characteristics). IN to BAT via the step-down switching regulator. An
FBG (Pin 11, LTC4120 Only):
Feedback Ground Pin. inductor should be connected from SW to CHGSNS. See This pin disconnects the external FB divider load from the Applications Information section for a discussion of the battery when it is not needed. When sensing the bat- inductor selection. tery voltage this pin presents a low resistance, RFBG, to
GND (Pin 5, Exposed Pad Pin 17):
Ground Pin. Connect GND. When in disabled or shutdown modes this pin is to exposed pad. The exposed pad must be soldered to high impedance. PCB GND to provide a low electrical and thermal imped-
NTC (Pin 12):
Input to the Negative Temperature Coefficient ance connection to ground. Thermistor Monitoring Circuit. The NTC pin connects to
DHC (Pin 6):
Dynamic Harmonization Control Pin. a negative temperature coefficient thermistor which is Connect a Schottky diode from the DHC pin to the IN pin, typically co-packaged with the battery to determine if the and a capacitor from the DHC pin as shown in the Typical battery is too hot or too cold to charge. If the battery’s Application or the Block Diagram. When VIN is greater temperature is out of range, the LTC4120 enters standby than VIN(DHC), this pin is high impedance. When VIN is mode and charging is paused until the battery tempera- below VIN(DHC) this pin is low impedance allowing the ture re-enters the valid range. A low drift bias resistor is LTC4120 to modulate the resonance of the tuned receiver required from INTVCC to NTC and a thermistor is required network. See Applications Information for more informa- from NTC to GND. Tie the NTC pin to GND to disable NTC tion on the tuned receiver network. qualified charging if NTC functionality is not required.
FREQ (Pin 7):
Buck Switching Frequency Select Input Pin.
PROG (Pin 13):
Charge Current Program and Charge Connect to INTVCC to select a 1.5MHz switching frequency Current Monitor Pin. Connect a 1% resistor between or GND to select a 750kHz switching frequency. Do not float. 3.01k (400mA) and 24.3k (50mA) from PROG to ground
CHGSNS (Pin 8):
Battery Charge Current Sense Pin. An to program the charge current. While in constant-current internal current sense resistor between CHGSNS and BAT mode, this pin regulates to 1.227V. The voltage at this pin pins monitors battery charge current. An inductor should represents the average battery charge current using the be connected from SW to CHGSNS. following formula:
BAT (Pin 9):
Battery Output Pin. Battery charge current is VPROG delivered from this pin through the internal charge current IBAT = hPROG • RPROG Rev. G For more information www.analog.com 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Test Circuit Operation Applications Information Package Description Revision History Typical Application Related Parts