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LM3621M-3.0 Scheda tecnica(PDF) 10 Page - National Semiconductor (TI) |
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LM3621M-3.0 Scheda tecnica(HTML) 10 Page - National Semiconductor (TI) |
10 / 14 page Application Information Battery Charger Operation Information Figure 4 shows a general battery charger configuration using LM3621. The LM3621 provides all the necessary control functions for charging Lithium-Ion batteries precisely and safely. It features constant voltage and constant current mode operation. The on chip timer provides all critical timing functions to properly initialize the charging cycle, avoid over charging the battery above its maximum capacity level, and cut off charging to a defective battery. The LM3621 also pro- vides the high accuracy of output voltage regulation without requiring a trim pot or precision resistors. A built-in power down switch prevents the battery from discharging through the LM3621. Input Supply Voltage The voltage supply to LM3621 must never exceed 6.0V or catastrophic damage may occur to the IC. When power is first applied to the battery charger, the LM3621 will remain in a reset state until the voltage on the V DD pin exceeds 3.4V for at least one second. This ensures that the power source is stable before a charge cycle is initiated. Figure 2 shows the state diagram for the charge cycle operation. Once the LM3621 emerges from the reset state after power up, it will not go into the reset state again until the voltage on the V DD pin drops below approximately 2.2V. When the LM3621 is in the reset state, the PFD (Pass FET Drive) pin is pulled low so that current is not allowed to flow into the load (e.g., Li+ battery). The LM3621 transitions from the reset state to standby mode when the conditions for a stable power source are met. Digital Control Inputs The LM3621 has four digital input control pins: Enable, Boost, V SET and ChgInt. To ensure proper operation, never allow unused digital input pins to be left open circuited. En- able is used to initiate a charge cycle, Boost is used to in- crease the maximum regulation current output, V SET con- trols the maximum output voltage, and ChgInt is used to instantaneously interrupt (and resume) a charge cycle in progress. Current Boost Mode This mode is activated when the “Boost” pin is pulled high. The charger increases the maximum output current equal to aV CSR level of 0.9V. This mode of operation is overridden by a charge interrupt signal. Charge Interrupt Control Charging is interrupted with the digital input “ChgInt” pulled low. The PFD pin is pulled to ground turning off the series low pass FET. This is useful to prevent charging a battery if, for example, the ambient temperature is excessively high. DS100107-4 FIGURE 4. General Application Circuit www.national.com 10 |
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