QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 783 NIMH/NICD CHARGER LTC4060 DESCRIPTION Demonstration circuit 783 is a complete Fast Battery to internal copper layers to maximize the power Charger capable of charging 1, 2, 3 or 4 series con- dissipation capabilities. Since this is a linear charger, nected NiMH or NiCd cells. Charge termination in- cludes - V, peak voltage and a safety timer. Included under some conditions, the power dissipated by the on the board are jumpers to select NTC thermistor charger can be high. To minimize power dissipation, functions, battery chemistry, number of series cells, close attention to the input voltage must be ob- safety timer length, recharge voltage and two LEDs served. to indicate charger status. A power path FET is also included that provides a low loss path between the Charging NiMH or NiCd batteries. battery and an external system load when the input power is removed. Terminals are included for PAUSE Nickel based batteries are typically charged with a and SHUTDOWN. constant current and allowing the battery voltage to rise to the level it requires (within limits) to force this The power portion of the circuit consists of a PNP current. When batteries are fast charged (1 to 2 power transistor constant current source which can hours) the charge cycle must be terminated when provide up to 2A of charge current under some con- the battery reaches full charge. This demo circuit ditions. Jumpers are provided for programming charge currents of 0.5A, 1A or 2A. Other charge cur- determines when the battery is fully charged using rents can be programmed by adding an external re- the - V method with peak voltage and timer as a sistor to the PROG terminal post. Charge current backup termination. greater than 2A can also be programmed by parallel- ing an external current sense resistor (R5) with the The V method measures the battery voltage as it internal LTC4060 sense resistor). See Extending is being charged with a constant current. The voltage Charge Current section of the data sheet for more will rise as the battery accepts charge. When it ap- information. For more power dissipation capability proaches full charge, the battery voltage will begin than the pc board can provide, terminals are in- rising faster, reach a peak, then begin to drop. When cluded for adding an external PNP pass transistor the battery voltage drops a fixed number of mV (de- mounted on a suitable heat sink. pending on battery chemistry), the battery is fully charged and the charge cycle terminates. Also included on this board is a power path MOSFET that provides a low resistance path between the bat- For the - V charge termination method to work cor- tery and a load (SYSTEM LOAD) when the input rectly, the charge current must be programmed to a power is removed. When the input voltage is pre- sufficiently high current level (C/2 to 2C). C is a sent, the load is powered from the input voltage. measure of cell capacity in mAHr. For example, to charge an 1800 mAHr battery at 1C would require a The pc board used for this demo circuit is a 4 layer charge current of 1.8A. board with generous amounts of copper surrounding the heat producing components. It also includes vias Design files for this circuit board are available. Call the LTC Factory. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 783 NIMH/NICD CHARGER QUICK START PROCEDURE FEATURES INCLUDE: TEST EQUIPMENT REQUIRED FOR DEMO BOARD EVALUATION: Jumper to select battery chemistry, NiMH or NiCd Lab Power supply for input power. 0 to 10V 2A Jumpers to select number of cells Digital multimeter for measuring battery voltage Jumper to select NTC Thermistor function (V ). 3-1/2 digits BAT Jumper to select recharge voltage level Digital multimeter for measuring charge current Jumper to select safety timer period Jumper to select charge (0.5A, 1A & 2A) 4 cell, 2000 mAHr NiCd or NiMH battery pack (10kW Terminals for custom timer periods and charge NTC thermistor optional) current 10W 10W power resistor for System Load (optional). Terminals for system load Resistor pads for optional external current sense resistor LEDs to indicate charger status o ACPR Sufficient input voltage for charging o CHRG Charging TYPICAL DEMO BOARD SPECIFICATIONS Minimum Input Voltage (1 series cell) - 4.5V (2 series cells) - 4.5V (3 series cells) - 6.9V (4 series cells) - 8.6V Maximum Input Voltage - 10V Constant Charge Current - 0.5A, 1A & 2A (8%) Safety Timer - 1.5Hrs & 3Hrs (20%) - V Termination (NiCd) - 16mV ( 2mV) - V Termination (NiMH) - 8mV ( 1.5mV) Recharge Threshold Voltage-OFF, 1.2V & 1.3V (5%) Precharge Current - 20% of Programmed Current (8%) 2