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DS2712Z+T Datasheet(PDF) 10 Page - Maxim Integrated Products |
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DS2712Z+T Datasheet(HTML) 10 Page - Maxim Integrated Products |
10 / 15 page DS2711/DS2712: Loose-Cell NiMH Chargers 10 of 15 Charge Timer The charge timer monitors the duration of charge in fast and top-off charge phases, and is reset at the beginning of each phase. The timeout period is set with an external resistor connected from the TMR pin to VSS. Resistors can be selected to support fast-charge timeout periods of 0.5 to 10 hours and top-off charge timeout periods of 0.25 to 5 hours. If the timer expires in fast-charge, the timer count is reset and charging proceeds to the top-off charge phase. The top-off timeout period is half of the fast charge timeout period. If the timer expires in top-off, charging proceeds to the maintenance phase. The programmed charge time approximately follows the equation: t = 1.5 x R/1000 (time in minutes) Suspend Suspension of charge activity is possible by disconnecting the TMR pin. The CC1 and CC2 outputs become high-Z and the charge timer stops. The state machine and all timers are reset to their presence test conditions. Temperature Sense Connecting an external 10k Ω NTC thermistor between THM1 or THM2 (THMx) and V SS, and a 10kΩ bias resistor between VDD and THMx allows the DS2711 to sense temperature. To sense the temperature of the battery cells, locate the thermistor close to the body of the battery cell so THM1 monitors the temperature of cell-1 and THM2 monitors the temperature of cell-2. Alternatively, the thermistor can sense ambient temperature by locating it away from the cells. THM1 and THM2 can be connected together to sense temperature using a single thermistor and bias resistor. The temperature qualification function can be defeated by connecting THM1 and THM2 to a single resistor-divider supplying a voltage between the Thermistor-Min and Thermistor-Max threshold voltages. Several recommended 10k Ω thermistors are shown in Table 2. Min, Max Temperature Compare The voltage thresholds of the THMx inputs (VTHM-MIN, VTHM-MAX) are set to allow fast charging to start if 0 °C < TA < 45°C when using the recommended 10kΩ bias and 10kΩ thermistor. If fast charging is in progress, and the voltage on THMx reaches VTHM-STOP, fast charging stops and the maintenance phase begins. Table 1. THM1, THM2 Thresholds THM THRESHOLD RATIO OF VDD THERMISTOR RESISTANCE ( Ω) TEMPERATURE ( °C) Semitec 103AT-2 Fenwal 197-103LAG-A01 173-103LAF-301 MIN 0.73 27.04k 0 4 MAX 0.33 4.925k 45 42 STOP 0.29 4.085k 50 47 Figure 7. Cell Voltage Sense Points Vcell1 Vcell2 VN1 VN0 VP1 VP2 Charge Source Vcell1 Vcell2 CC1 CC1 CC2 VP1 VN1 VP2 VN0 Series Configuration Parallel Configuration Charge Source |
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