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LTC4095 Datasheet(PDF) 9 Page - Linear Technology |
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LTC4095 Datasheet(HTML) 9 Page - Linear Technology |
9 / 16 page LTC4095 9 4095fa OPERATION In any mode, the actual battery current can be determined by monitoring the PROG pin voltage and using the follow- ing equation: I PROG R BAT PROG = •800 Thermal Regulation To prevent thermal damage to the IC or surrounding components, an internal thermal feedback loop will automatically decrease the programmed charge current if the die temperature rises to approximately 115°C. Thermal regulation protects the LTC4095 from excessive temperature due to high power operation or high ambient thermal conditions and allows the user to push the limits of the power handling capability with a given circuit board design without risk of damaging the LTC4095 or external components. The benefit of the LTC4095 thermal regula- tion loop is that charge current can be set according to actual conditions rather than worst-case conditions with the assurance that the battery charger will automatically reduce the current in worst-case conditions. Charge Status Indication The ⎯C⎯H⎯R⎯G pin indicates the status of the battery charger. Four possible states are represented by ⎯C⎯H⎯R⎯G: charging, not charging, unresponsive battery and battery temperature out of range. The signal at the ⎯C⎯H⎯R⎯G pin can be easily recognized as one of the above four states by either a human or a micropro- cessor. The ⎯C⎯H⎯R⎯G pin, which is an open-drain output, can drive an indicator LED through a current limiting resistor for human interfacing, or simply a pull-up resistor for microprocessor interfacing. To make the ⎯C⎯H⎯R⎯G pin easily recognized by both humans and microprocessors, the pin is either a DC signal of ON for charging, OFF for not charging, or it is switched at high frequency (35kHz) to indicate the two possible faults: unresponsive battery and battery temperature out of range. When charging begins, ⎯C⎯H⎯R⎯G is pulled low and remains low for the duration of a normal charge cycle. When the charge current has dropped to below 10% of the full-scale current, the ⎯C⎯H⎯R⎯G pin is released (high impedance). If a fault occurs after the ⎯C⎯H⎯R⎯G pin is released, the pin re- mains high impedance. However, if a fault occurs before the ⎯C⎯H⎯R⎯G pin is released, the pin is switched at 35kHz. While switching, its duty cycle is modulated between a high and low value at a very low frequency. The low and high duty cycles are disparate enough to make an LED appear to be on or off thus giving the appearance of “blinking”. Each of the two faults has its own unique “blink” rate for human recognition as well as two unique duty cycles for microprocessor recognition. Table 1 illustrates the four possible states of the ⎯C⎯H⎯R⎯G pin when the battery charger is active. Table 1. ⎯C⎯H⎯R⎯G Output Pin STATUS FREQUENCY MODULATION (BLINK) FREQUENCY DUTY CYCLE Charging 0Hz 0 Hz (Lo-Z) 100% IBAT < C/10 0Hz 0 Hz (Hi-Z) 0% NTC Fault 35kHz 1.5Hz at 50% 6.25% to 93.75% Bad Battery 35kHz 6.1Hz at 50% 12.5% to 87.5% An NTC fault is represented by a 35kHz pulse train whose duty cycle varies between 6.25% and 93.75% at a 1.5Hz rate. A human will easily recognize the 1.5Hz rate as a “slow” blinking which indicates the out of range battery temperature while a microprocessor will be able to decode either the 6.25% or 93.75% duty cycles as an NTC fault. If a battery is found to be unresponsive to charging (i.e., its voltage remains below VTRKL for over 1/2 hour), the ⎯C⎯H⎯R⎯G pin gives the battery fault indication. For this fault, a human would easily recognize the frantic 6.1Hz “fast” blinking of the LED while a microprocessor would be able to decode either the 12.5% or 87.5% duty cycles as a bad battery fault. Although very improbable, it is possible that a duty cycle reading could be taken at the bright-dim transition (low duty cycle to high duty cycle). When this happens the duty cycle reading will be precisely 50%. If the duty cycle reading is 50%, system software should disqualify it and take a new duty cycle reading. |
Similar Part No. - LTC4095_15 |
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Similar Description - LTC4095_15 |
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