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MC33340 bảng dữ liệu(PDF) 8 Page - ON Semiconductor |
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MC33340 bảng dữ liệu(HTML) 8 Page - ON Semiconductor |
8 / 16 page MC33340, MC33342 http://onsemi.com 8 switching between the fast and trickle modes as the lower temperature limit is crossed. The amount of temperature rise to overcome the hysteresis is determined by the thermistor’s rate of resistance change or sensitivity at the under temperature trip point. The required resistance change is: DR(T Low ³ T High ) + VH(T) I in + 44 mV 30 mA + 1.46 k The resistance change approximates a thermal hysteresis of 2 °C with a 10 kW thermistor operating at 0°C. The under temperature fast charge inhibit feature can be disabled by biasing the t3/Tref Low input to a voltage that is greater than that present at t2/Tsen, and less than VCC − 0.7 V. Under extremely cold conditions, it is possible that the thermistor resistance can become too high, allowing the t2/Tsen input to go above VCC − 0.7 V, and activate the timer. This condition can be prevented by placing a resistor in parallel with the thermistor. Note that the time/temperature threshold of VCC − 0.7 V is a typical value at room temperature. Refer to the Electrical Characteristics table and to Figure 4 for additional information. The upper comparator senses the presence of an over temperature condition. When the upper temperature limit is exceeded, the comparator output sets the Overtemperature Latch and the charger is switched to trickle mode. Once the latch is set, the charger cannot be returned to fast charge, even after the temperature falls below the limit. This feature prevents the battery pack from being continuously temperature cycled and overcharged. The latch can be reset by removing and reconnecting the battery pack or by cycling the power supply voltage. If the charger does not require either the time or temperature backup features, they can both be easily disabled. This is accomplished by biasing the t3/Tref Low input to a voltage greater than t2/Tsen, and by grounding the t1/Tref High input. Under these conditions, the Time/Temp Select comparator output is low, indicating that the temperature mode is selected, and that the t2/Tsen input is biased within the limits of an artificial temperature window. Charging of battery packs that are used in portable power tool applications typically use temperature as the only means for fast charge termination. The MC33340/342 can be configured in this manner by constantly resetting the − DV detection logic. This is accomplished by biasing the Vsen input to ≈1.5 V from a two resistor divider that is connected between the positive battery pack terminal and ground. The Vsen Gate output is also connected to the Vsen input. Now, each time that the Sample Timer causes the Vsen output to go low, the Vsen input will be pulled below the undervoltage threshold of 1.0 V. This causes a reset of the − DV logic every 1.38 seconds, thus disabling detection. Operating Logic The order of events in the charging process is controlled by the logic circuitry. Each event is dependent upon the input conditions and the chosen method of charge termination. A table summary containing all of the possible operating modes is shown in Table 2. Table 1. FAST CHARGE BACKUP TERMINATION TIME/TEMPERATURE LIMIT Backup Termination Mode Programming Inputs Time Limit Fast Charge (Minutes) t3/Tref Low (Pin 5) t2/Tsen (Pin 6) t1/Tref High (Pin 7) Time Open Open Open 283 Time Open Open GND 247 Time Open GND Open 212 Time Open GND GND 177 Time GND Open Open 141 Time GND Open GND 106 Time GND GND Open 71 Temperature 0 V to VCC − 0.7 V 0 V to VCC − 0.7 V 0 V to VCC − 0.7 V Timer Disabled |
Số phần tương tự - MC33340 |
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Mô tả tương tự - MC33340 |
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