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LTC4008EGN-1 Datasheet(PDF) 10 Page - Linear Technology |
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LTC4008EGN-1 Datasheet(HTML) 10 Page - Linear Technology |
10 / 24 page 10 LTC4008 4008fa If the charging current decreases below 10% to 15% of programmed current, while engaged in input current limiting, BGATE will be forced low to prevent the charger from discharging the battery. Audible noise can occur in this mode of operation. An overvoltage comparator guards against voltage tran- sient overshoots (>7% of programmed value). In this case, both MOSFETs are turned off until the overvoltage condition is cleared. This feature is useful for batteries which “load dump” themselves by opening their protec- tion switch to perform functions such as calibration or pulse mode charging. PWM Watchdog Timer There is a watchdog timer that observes the activity on the BGATE and TGATE pins. If TGATE stops switching for more than 40 µs, the watchdog activates and turns off the top MOSFET for about 400ns. The watchdog engages to prevent very low frequency operation in dropout which is a potential source of audible noise when using ceramic input and output capacitors. Charger Startup When the charger is enabled, it will not begin switching until the ITH voltage exceeds a threshold that assures initial current will be positive. This threshold is 5% to 15% of the maximum programmed current (100mV/RSENSE). After the charger begins switching, the various loops will control the current at a level that is higher or lower than the initial current. The duration of this transient condition depends upon the loop compensation but is typically less than 100 µs. Thermistor Detection The thermistor detection circuit is shown in Figure 3. It requires an external resistor and capacitor in order to function properly. OPERATIO ICHARGE (% OF MAXIMUM CURRENT) 0 0 0.2 0.4 0.6 0.8 4008 F02 1.0 1.2 20 40 60 80 100 1.19V 0.309V Figure 2. VPROG vs ICHARGE 8 NTC LTC4008 S1 R10 32.4k C7 0.47 µF RTH 10k NTC – + – + – + 60k ~4.5V CLK 45k 15k TBAD 4008 F03 D C Q Figure 3 |
Similar Part No. - LTC4008EGN-1 |
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Similar Description - LTC4008EGN-1 |
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