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LTC4060 Datasheet(PDF) 11 Page - Linear Integrated Systems |
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LTC4060 Datasheet(HTML) 11 Page - Linear Integrated Systems |
11 / 20 page 11 LTC4060 4060f OPERATIO charging begins at the maximum current set by the external programming resistor connected between the PROG pin and GND. If an external thermistor indicates sensed temperature is beyond a range of 5°C to 55°C charging is suspended, the charge timer is paused and the CHRG status output remains low. Normal charging resumes from the previous state when the sensed temperature rises above 5°C or falls below 45°C. Voltage-based termination (–∆V) is then reset and immediately enabled. If voltage-based termina- tion was imminent when the temperature limits were exceeded, charge termination will occur. Charge Termination Once fast charge begins and after an initial battery voltage stabilization hold-off period shown in Table 1, voltage- based termination (–∆V) is enabled. This period is used to prevent falsely terminating on a –∆V event that can occur almost immediately after initiating charging on some heavily discharged or stored batteries. However, if VCELL was measured to be above 1.3V (VIDT) immediately prior to the precharge cycle, then a mostly charged battery is assumed and voltage-based termination (–∆V) is enabled without delay. An internal 1.5mV resolution A/D converter measures the cell voltage after each battery voltage sampling interval indicated in Table 1. The peak cell voltage is stored and compared to the current cell voltage. When the cell voltage has dropped by at least VMDV (magnitude selected by the CHEM pin) from the peak for four consecutive battery voltage sampling intervals, charging is terminated. Back-up termination is provided by the charge time limiter, whose time limit is indicated in Table 1, and by a battery overvoltage detector. Once terminated by back-up termi- nation, charge qualification can be reinitiated only by remov- ing and replacing the battery or toggling the SHDN pin low to high or removing and reapplying power to the charger. Automatic Recharge Once charging is complete, the optional programmable automatic recharge state can be entered. This state, if enabled, will automatically restart the charger from the charge qualification state without user intervention when- ever the battery cell voltage drops below a set level. With the advent of low memory effect NiMH and improved NiCd cells an automatic recharge feature is practical and elimi- nates the need for very slow trickle charging. The CHRG status output is high impedance in the auto- matic recharge state until charging begins. If the VCELL voltage drops below the voltage set on the ARCT pin for at least the automatic recharge entry delay time as shown in Table 1, the charge qualification state is entered and charging will begin anew in fast charge. An easy way of setting the voltage on the ARCT pin is by using two series current programming resistors and connecting their com- mon to the ARCT pin as shown in Figure 2. The PROG pin will provide a constant 1.5V (VPROG). The programmable voltage range of the ARCT pin is approximately 0.8V to 1.6V. A preprogrammed recharge threshold of 1.3V (VARDT) is selected when the ARCT pin is connected to VCC (VARDEF). Automatic recharge is disabled when the ARCT pin is connected to ground (VARDIS). Pause After charging is initiated, the PAUSE pin may be used to pause operation at any time. Whenever the voltage on the PAUSE pin is a logic high, the charge timer and all other timers pause, charging is stopped and the fast charge ter- mination algorithm is inhibited. The CHRG status output remains at GND. If voltage-based termination was immi- nent before pause, charge termination will occur. Otherwise, when pause ends, the charge timer and all other timers resume timing, charging restarts and voltage-based termi- nation (–∆V) is reset and immediately enabled. If the bat- tery is removed while the PAUSE pin is a logic high, then battery removal is detected and shutdown is entered. If the battery is replaced while the PAUSE pin is a logic high, it will not be detected until pause is turned off. For pause periods or a series of periods where the battery capacity could be significantly depleted, consider using shutdown instead of pause to avoid having the safety timer expire before the battery can be fully charged. Shutdown resets the safety timer. |
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