DC788A Analog Devices

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 788A SINGLE CELL LI-ION BATTERY CHARGER WITH NTC LTC4061 DESCRIPTION Demonstration circuit 788A is a complete constant- vided for adding a thermistor for sensing battery tem- current, constant-voltage battery charger for one perature, shutting down the charger, monitoring Lithium-Ion cell. The LTC4061EDD used on this demo charge current and programming the minimum circuit features an internal P-Channel power MOSFET charge current level for termination (I ). An DETECT with a unique thermal feedback loop that reduces the LED indicates when the charge current has dropped output current under high ambient temperature below the minimum charge current termination level. and/or high power dissipation conditions. This feature The IC is available in a 10-Pin 3mm x 3mm DFN allows the charger to provide higher charge currents thermally enhanced package featuring an exposed under normal conditions and still provide safe charg- bottom-side metal pad for soldering to the PC board. ing under abnormal conditions such as high ambient temperature, high input voltage or low battery volt- age. Design files for this circuit board are available. Call the LTC factory. Jumpers on the board allow charge currents from 50mA to 1A to be programmed and several charge LTC is a trademark of Linear Technology Corporation termination methods to be used. Terminals are pro- Table 1. Typical Specifications (25C) Input Voltage Range V 4.3 to 8V (upper range limited by PC board power IN dissipation) Input UnderVoltage Lockout 3.8V Output Float Voltage V (constant voltage mode) 4.2V 0.5% BAT Output Current I (constant current mode) From 50mA to 1A 8% (selected by jumpers) BAT Current Monitor Output 1V 5% Full Current Charge Termination Timer 3 Hours 10% Charge Termination Threshold Current (I ) 25mA, 50mA, 100mA 10% DETECT 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 788A SINGLE CELL LI-ION BATTERY CHARGER WITH NTC OPERATION terminates the charge cycle when the charge cur- Demonstration circuit 788A allows three methods rent drops to a programmed threshold level after of charge termination which are selected using the battery has reached the constant voltage portion jumper JP1. In the lower Timer position, the of the charge cycle. Placing the jumper (JP1) in the charge cycle terminates at the end of the timer pe- middle position defeats the on board termination riod as set by capacitor C2. The 3 hour timer is suf- thus allowing external user termination. ficient time to fully charge a depleted battery when charging at a current level ranging from C/2 to 1C. The charge current and the termination current are selected using a combination of jumpers JP2, JP3 The upper ITERM position selects minimum and JP4. (See table 2) charge current termination (I ). This method DETECT Table 2. Jumper Positions for Charge Current and Termination Current. IDET JUMPER (JP4) 100MA C / 10 ICHG-1 ICHG-2 Charge Current Idetect Current Charge Current Idetect Current (JP3) (JP2) C 1A 100mA 500mA 50mA HIGH C / 5 200mA 100mA 100mA 50mA C 500mA 100mA 250mA 25mA LOW C/5 100mA 100mA 50mA 25mA The CHRG LED always indicates the presence of The current monitor terminal can be used to indi- charge current that is greater than the I cur- cate charge current level at all times during the DETECT rent level that is selected by the IDET jumper (JP4). charge cycle with 1 Volt indicating 100% of the The LED is on for charge current greater than IDET, programmed current. This terminal can also be regardless of the termination method used as set by used to program other charge currents by removing jumper JP1. jumper JP3 and connecting an external program- ming resistor from the current monitor terminal to When minimum charge current termination ground. See data sheet for details. (I ) is used, the charge cycle ends when the DETECT charge current drops below the I level. The DETECT CHRG LED also goes off. 2