Datasheet LTC4000 (Analog Devices) - 9

LTC4000
pin FuncTions (QFN/SSOP)
is not exceeded. The charge current limit is determined if the battery temperature is safe for charging. The charge using the following formula: current and charge timer are suspended if the thermistor  indicates a temperature that is unsafe for charging. Once the R  I CL temperature returns to the safe region, charging resumes. CLIM = 2.5µA •   RCS  Leave the pin open or connected to a capacitor to disable the temperature qualified charging function. Where RCS is the sense resistor connected to the CSP and the CSN pins. Leave the pin open for the maximum
FBG (Pin 15/Pin 11):
Feedback Ground Pin. This is the charge current limit of 50mV/R ground return pin for the resistor dividers connected to CS. the BFB and OFB pins. As soon as the voltage at IN is valid
TMR (Pin 9/Pin 5):
Charge Timer. Attach 1nF of external (>3V typical), this pin has a 100Ω resistance to GND. When capacitance (CTMR) to GND for each 104 seconds of charge the voltage at IN is not valid, this pin is disconnected from termination time and 26 seconds of bad battery indicator GND to ensure that the resistor dividers connected to the time. Short to GND to prevent bad battery indicator time BFB and OFB pins do not continue to drain the battery and charge termination time from expiring – allowing a when the battery is the only available power source. continuous trickle charge and top off float voltage regula- tion charge. Short to BIAS to disable bad battery detect
BFB (Pin 16/Pin 12):
Battery Feedback Voltage Pin. This and enable C/X charging termination. pin is a high impedance input pin used to sense the battery voltage level. In regulation, the battery float voltage loop
GND (Pins 10, 28, 29/Pins 6, 24):
Device Ground Pins. sets the voltage on this pin to 1.136V (typical). Connect Connect the ground pins to a suitable PCB copper ground this pin to the center node of a resistor divider between plane for proper electrical operation. The QFN package the BAT pin and the FBG pin to set the battery float voltage. exposed pad must be soldered to PCB ground for rated The battery float voltage can then be obtained as follows: thermal performance.
FLT, CHRG (Pin 11, Pin 12/Pin 7, Pin 8):
Charge Status VFLOAT = RBFB2 +RBFB1 • 1.136V R Indicator Pins. These pins are high voltage open drain pull BFB2 down pins. The FLT pin pulls down when there is an under
BAT (Pin 17/Pin 13):
Battery Pack Connection. Connect or over temperature condition during charging or when the battery to this pin. This pin is the anode of the battery the voltage on the BFB pin stays below the low battery ideal diode driver (the cathode is the CSN pin). threshold during charging for a period longer than the bad battery indicator time. The CHRG pin pulls down during
BGATE (Pin 18/Pin 14):
External Battery PMOS Gate Drive a charging cycle. Please refer to the application informa- Output. When not charging, the BGATE pin drives the tion section for details on specific modes indicated by the external PMOS to behave as an ideal diode from the BAT combination of the states of these two pins. Pull up each pin (anode) to the CSN pin (cathode). This allows efficient of these pins with an LED in series with a resistor to a delivery of any required additional power from the battery voltage source to provide a visual status indicator. Short to the downstream system connected to the CSN pin. these pins to GND when not used. When charging a heavily discharged battery, the BGATE
BIAS (Pin 13/Pin 9):
2.9V Regulator Output. Connect a pin is regulated to set the output feedback voltage (OFB capacitor of at least 470nF to bypass this 2.9V regulated pin) to 86% of the battery float voltage (0.974V typical). voltage output. Use this pin to bias the resistor divider to This allows the instant-on feature, providing an immedi- set up the voltage at the NTC pin. ate valid voltage level at the output when the LTC4000 is charging a heavily discharged battery. Once the voltage
NTC (Pin 14/Pin 10):
Thermistor Input. Connect a ther- on the OFB pin is above the 0.974V typical value, then the mistor from NTC to GND, and a corresponding resistor BGATE pin is driven low to ensure an efficient charging from BIAS to NTC. The voltage level on this pin determines path from the CSN pin to the BAT pin. 4000fb For more information www.linear.com/LTC4000 9 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