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ACT3704YH-T Datasheet(PDF) 10 Page - Active-Semi, Inc |
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ACT3704YH-T Datasheet(HTML) 10 Page - Active-Semi, Inc |
10 / 15 page ACT3704 Rev2, 26-Jul-07 Innovative Products. Active Solutions. - 10 - www.active-semi.com Copyright © 2007 Active-Semi, Inc. Top-Off State In the TOP-OFF state, the cell is charged in con- stant-voltage (CV) mode, with the charge current limited by the internal chemistry of the cell, decreas- ing as charging continues. If the ACT3704 state machine does not complete a charging cycle before the TOP-OFF Timeout period (TTOPOFF) expires, then a damaged cell is detected and the state machine jumps to the TIMEOUT- FAULT State. The TOP-OFF Timeout period is default to 60mins with a 2.2nF CTIMER capacitor, or it can be increased with a larger value external capacitor. See the Safety Timers section for more information. In TOP-OFF state, nSTAT indicates charge com- plete but charge current still continues. After another delay of 60mins, then charging stops and charge current becomes zero. When the battery voltage drops below the charge restart voltage, the charging process will start again. End of Charge State In the End of Charge (EOC) state, the ACT3704 presents a high-impedance to the battery, allowing the cell to “relax” and minimize battery leakage cur- rent. The ACT3704 continues to monitor the cell voltage, however, so that it can reinitiate charging cycles as necessary to ensure that the cell remains fully charged. Charge Restart Under normal operation, the state machine initiates a new charging cycle by jumping to the NORMAL CHARGE state when VBAT drops below the Charge Termination Threshold by more than the Charge Re- start Threshold of 100mV (typ). Timeout-Fault State In TIMEOUT-FAULT state, both nSTAT and nEOC indicators are OFF, or high-Z. Charge and EOC Status Outputs nSTAT and nEOC are open-drain outputs that sink current when asserted and are high-Z otherwise. For more information regarding the state of nSTAT and nEOC throughout the entire charging cycle, see Ta- ble 3. These outputs have internal 7mA current lim- its, and are capable of directly driving LEDs, without the need of current-limiting resistors or other exter- nal circuitry, for a visual charge-status indication. To drive an LED, simply connect the LED between each pin and an appropriate supply (typically VIN). For a logic-level indication, simply connect a resistor from each output to an appropriate voltage supply. Reverse Battery & Shutdown The ACT3704 includes internal circuitry that elimi- nates the need for series blocking diodes, reducing solution size and cost as well as dropout voltage relative to conventional battery chargers. When VIN goes below the ACT3704’s under voltage-lockout (UVLO) voltage, or when VIN drops below VBAT, the ACT3704 automatically goes into SUSPEND mode and reconfigures its power switch to minimize cur- rent drain from the battery. Safety Timers The ACT3704 has several internal charge safety timers, for each of the PRECONDITION and NOR- MAL charge states as well as TOPOFF timeout pe- riod. If any of these timers expire before charge suc- cessfully proceeds through the associated state, the ACT3704 enters the TIMEOUT-FAULT state. The TIMEOUT-FAULT state can only be reset by power- cycling the ACT3704. Each of these timers are internally set according to the following ratios: All the timers could be set by an external capacitor by (CTIMER in nF) where TO is given by: When operating in thermal regulation mode the timeout periods are extended in order to compen- sate for the effect of the reduced charging current on total charge time. In order to ensure a safe charge, the maximum timeout periods are limited to 2x the room temperature values. O ON PRECONDITI T 1 T × = O NORMAL T 5 . 1 T × = O TOTAL T 3 T × = % 15 C 9 T TIMER O ± × = (9) (10) (11) (12) |
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