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DS2714E+ Datasheet(PDF) 9 Page - Maxim Integrated Products |
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DS2714E+ Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 12 page DS2714: Quad Loose Cell NiMH Charger 9 of 12 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 time-out period is set with an external resistor connected from the TMR pin to VSS. Resistors can be selected to support Fast charge time-out periods of 0.5 to 10 hours and Top-off charge time-out 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 time-out period is half of the Fast charge time-out period. When the timer expires in Top-Off, charging proceeds to the Maintenance phase. The programmed charge time approximately follows the equation: t = 1.5 * R / 1000 (time in minutes) SUSPEND Suspension of charge activity is possible by floating the TMR pin. All CCx 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 10kΩ NTC thermistor between THM1 or THM2 (THMx) and VSS, and a 10kΩ bias resistor between VDD and THMx allows the DS2714 to sense temperature. In order to sense the temperature of the battery cells, locate the thermistor close to the body of the battery cell. The THM1 thermistor should be placed between cells 1 and 2, and THM2 thermistor between cells 3 and 4. Alternatively, the thermistors can sense ambient temperature by locating them away from the cells. THM1 and THM2 can be tied together to sense temperature using a single thermistor and bias resistor. The temperature qualification function can be defeated by tying THMx pins to a single resistor divider supplying a voltage between the Thermistor-Min and Thermistor-Max threshold voltages. 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 (TA > 50 °C), Fast charging stops and the maintenance phase begins. In Pre-charge the device will transition to the Fault state if the voltage on THMx reaches VTHM-STOP. Table 1. THM1, THM2 Thresholds TEMPERATURE THM THRESHOLD RATIO OF VDD THERMISTOR RESISTANCE Semitec 103AT-2 Fenwal 197-103LAG-A01 173-103LAF-301 MIN 0.73 27.04k 0C 4C MAX 0.33 4.925k 45C 42C STOP 0.29 4.085k 50C 47C CELL VOLTAGE MONITORING Individual cell voltages are monitored for minimum and maximum values, using the VBAT-LOW , VBAT-MAX1 and VBAT- MAX2 threshold limits. Upon inserting a cell or power-up with cells inserted, cell voltages must be less than the VBAT- MAX1 threshold before charging begins. The VBAT-LOW threshold determines whether a Pre-charge cycle should precede the Fast charge cycle, and when to transition from Pre-charge to Fast charge. Once Fast charging commences, cell voltages are compared to the VBAT-MAX2 threshold once every 2 seconds. The comparison occurs while the charge control pin (CC1-4) controlling current to the cell is active (low). When the charge control pin is active such that charge is applied to the cell, the cell voltage is referred to as the VON voltage. When the charge control pin is inactive, the cell voltage is referred to as the VOFF voltage. Charging is halted and a Fault condition is displayed if VON is greater than VBAT-MAX2. Charging is also halted and a fault condition is entered if VOFF is greater than VBAT-MAX1. While Fast charge is in progress, cell voltage measurements are stored and compared to future measurements for charge termination and cell test purposes. |
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