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LTC1729 Datasheet(PDF) 10 Page - Linear Technology |
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LTC1729 Datasheet(HTML) 10 Page - Linear Technology |
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10 / 16 page  10 LTC1729 Series Status Output Pin The STATUS pin is designed to provide an indication that the battery is charging. Once the current drops below the C/10 threshold, the battery is close to being fully charged. The LTC1729 turns off the hard pull-down once the C/10 comparator is active for more than three seconds. The 50 µA soft pull down remains in effect until the 3-hour time-out is completed or the input power is removed. By using two different value pull-up resistors, a micropro- cessor can detect three states from this pin (charging, C/10 and stop charging). See Figure 7. Second, if the battery is removed from the charger, the VMAX signal is activated as mentioned in the Block Dia- gram section. This causes the state machine to make the VBAT > VMAX transition to the Pause state. The third way to exit the charger “ON” state is with a VBAT < VMIN transition to the Precondition state. The battery will need to drop below 2.6V/cell to be less than VMIN. This is not a likely scenario. Once in the Pause state, there are two ways to proceed. The first is to go to the No Bat state. This requires that the VBAT remain greater than VMAX for more than one second. From these conditions, the LTC1729 interprets that a battery has been removed. If the voltage on the BAT pin stays less than VMAX for more than one second, then the state machine returns to the Charge state (Precondi- tion and charger “ON”). This is interpreted as a momentary open caused by the battery pack protection circuitry or loose contact. The Done state can only proceed to the No Bat state. From outside the LTC1729 this transition is undetectable. The requirement for this transition is for the BAT pin voltage to exceed VMAX for more than one second. The IC now assumes that the battery has been removed. From the No Bat state, there is only one possible transition. The No Bat state can move to the Charge state if the voltage on the BAT pin remains less than VMAX for one second. The LTC1729 will now work on the assumption that a new battery has been installed. Although the Precondition and Charger “ON” both reside in the Charge state, there are differences between these states. The main purpose of the Precondition state is to slowly bring a heavily discharged battery up to a minimum level before full charge current begins. The Precondition state uses a 12mA current source to trickle charge the battery with a 1-hour time-out transition to the Done state. The Charger “ON” state enables the external charger and the time-out is increased to three hours. For the entire time in the Precondition state, the STATUS pin uses a hard pull-down. In the Charger “ON” state the STATUS pin uses two types of pull-down: hard pull-down and soft 50 µA pull-down. APPLICATIO S I FOR ATIO 3k 200k STATUS 1729 F07 VCC LTC1729 VIN VDD OUT µPROCESSOR IN 6 8 Figure 7. Microprocessor Interface When the LTC1729 is in charge mode, the STATUS pin is pulled down by an internal N-channel MOSFET. To detect this mode, force the digital output pin, OUT, high and measure the voltage at the STATUS pin. The N-channel MOSFET will pull the pin low even with a 3k pull-up resis- tor. Once the charge current drops to 10% of the full-scale current (C/10), the N-channel MOSFET is turned off and a 50 µA current source is connected to the STATUS pin. The IN pin will then be pulled high by the 3k pull-up. By forcing the OUT pin into a high impedance state, the current source will pull the pin low through the 200k resistor. When the internal timer has expired, the STATUS pin will change to high impedance state and the 200k resistor will then pull the pin high to indicate the charging has stopped. Terminate at C/10 Current Charging can also be terminated using C/10 detection before the 3-hour time-out. By connecting the low side of the NTC thermistor to the STATUS pin instead of ground, |
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Similar Description - LTC1729 |
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