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LTC4096EDD Datasheet(PDF) 10 Page - Linear Technology |
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LTC4096EDD Datasheet(HTML) 10 Page - Linear Technology |
10 / 16 page LTC4096/LTC4096X 10 4096xf Programming Charge Termination The charge cycle terminates when the charge current falls below the programmed termination threshold during constant-voltage mode. This threshold is set by connect- ing an external resistor, RITERM, from the ITERM pin to ground. The charge termination current threshold (ITERMINATE) is set by the following equation: R V I I V R ITERM TERMINATE TERMINATE ITERM == 100 100 , The termination condition is detected by using an internal filtered comparator to monitor the ITERM pin. When the ITERM pin voltage drops below 100mV* for longer than tTERMINATE (typically 3ms), the charge cycle terminates, charge current latches off and the LTC4096 enters standby mode. When charging, transient loads on the BAT pin can cause the ITERM pin to fall below 100mV for short periods of time before the DC charge current has dropped below the programmed termination current. The 3ms filter time (tTERMINATE) on the termination comparator ensures that transient loads of this nature do not result in premature charge cycle termination. Once the average charge current drops below the programmed termination threshold, the LTC4096 terminates the charge cycle and stops providing any current out of the BAT pin. In this state, any load on the BAT pin must be supplied by the battery. Low-Battery Charge Conditioning (Trickle Charge) This feature ensures that deeply discharged batteries are gradually charged before applying full charge current. If the BAT pin voltage is below 2.9V, the LTC4096 supplies 1/10th of the full charge current to the battery until the BAT pin rises above 2.9V. For example, if the charger is programmed to charge at 800mA from the wall adapter input and 500mA from the USB input, the charge current OPERATION *Any external sources that hold the ITERM pin above 100mV will prevent the LTC4096 from terminating a charge cycle. during trickle charge mode would be 80mA and 50mA, respectively. The LTC4096X has no trickle charge mode. Automatic Recharge In standby mode, the charger sits idle and monitors the battery voltage using a comparator with a 1.6ms filter time (tRECHRG). A charge cycle automatically restarts when the battery voltage falls below 4.15V (which corresponds to approximately 80%-90% battery capacity). This ensures that the battery is kept at, or near, a fully charged condi- tion and eliminates the need for periodic charge cycle initiations. If the battery is removed from the charger, a sawtooth waveform appears at the battery output. This is caused by the repeated cycling between termination and recharge events. This cycling results in pulsing at the ⎯C⎯H⎯R⎯G output; an LED connected to this pin will exhibit a blinking pattern, indicating to the user that a battery is not present. The frequency of the sawtooth is dependent on the amount of output capacitance. Status Indicators The charge status output ( ⎯C⎯H⎯R⎯G)hastwostates:pull-down and high impedance. The pull-down state indicates that the LTC4096 is in a charge cycle. Once the charge cycle has terminated or the LTC4096 is disabled, the pin state becomes high impedance. The pull-down state is capable of sinking up to 10mA. The power present output (PWR) has two states: DCIN/ USBIN voltages and high impedance. These states are described in Table 1 and the circuit is shown in Figure 2. The high impedance state indicates that voltage is not present at either DCIN or USBIN, so LTC4096 lacks sufficient power to charge the battery. The PWR present output is capable of sourcing up to 120mA steady state and includes short circuit protection. |
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