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MAX712CPE Datasheet(PDF) 8 Page - Maxim Integrated Products |
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MAX712CPE Datasheet(HTML) 8 Page - Maxim Integrated Products |
8 / 17 page NiCd/NiMH Battery Fast-Charge Controllers 8 _______________________________________________________________________________________ Detailed Description The MAX712/MAX713 fast charge NiMH or NiCd batter- ies by forcing a constant current into the battery. The MAX712/MAX713 are always in one of two states: fast charge or trickle charge. During fast charge, the current level is high; once full charge is detected, the current reduces to trickle charge. The device monitors three variables to determine when the battery reaches full charge: voltage slope, battery temperature, and charge time. Figure 1 shows the block diagram for the MAX712/ MAX713. The timer, voltage-slope detection, and temper- ature comparators are used to determine full charge state. The voltage and current regulator controls output voltage and current, and senses battery presence. Figure 2 shows a typical charging scenario with batteries already inserted before power is applied. At time 1, the MAX712/MAX713 draw negligible power from the bat- tery. When power is applied to DC IN (time 2), the power-on reset circuit (see the POWER - _ON - _RESET sig- nal in Figure 1) holds the MAX712/MAX713 in trickle charge. Once POWER - _ON - _RESET goes high, the device enters the fast-charge state (time 3) as long as the cell voltage is above the undervoltage lockout (UVLO) volt- age (0.4V per cell). Fast charging cannot start until (bat- tery voltage) / (number of cells) exceeds 0.4V. When the cell voltage slope becomes negative, fast charge is terminated and the MAX712/MAX713 revert to trickle-charge state (time 4). When power is removed (time 5), the device draws negligible current from the battery. Figure 3 shows a typical charging event using tempera- ture full-charge detection. In the case shown, the bat- tery pack is too cold for fast charging (for instance, brought in from a cold outside environment). During time 2, the MAX712/MAX713 remain in trickle-charge state. Once a safe temperature is reached (time 3), fast charge starts. When the battery temperature exceeds the limit set by THI, the MAX712/MAX713 revert to trick- le charge (time 4). 0 A mA µA 1 0.4 TIME VOLTAGE 1.4 1.5 1.3 2 4 5 3 1. NO POWER TO CHARGER 2. CELL VOLTAGE LESS THAN 0.4V 3. FAST CHARGE 4. TRICKLE CHARGE 5. CHARGER POWER REMOVED TEMPERATURE Figure 2. Typical Charging Using Voltage Slope A mA µA 1 TIME TLO THI 24 3 1. NO POWER TO CHARGER 2. CELL TEMPERATURE TOO LOW 3. FAST CHARGE 4. TRICKLE CHARGE Figure 3. Typical Charging Using Temperature A 1.5 1.4 1.3 mA µA 1 TIME VREF = VLIMIT 24 3 1. BATTERY NOT INSERTED 2. FAST CHARGE 3. TRICKLE CHARGE 4. BATTERY REMOVED Figure 4. Typical Charging with Battery Insertion |
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