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L6924U013 Folha de dados(PDF) 11 Page - STMicroelectronics |
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L6924U013 Folha de dados(HTML) 11 Page - STMicroelectronics |
11 / 37 page L6924U Operation description Doc ID 14716 Rev 2 11/37 6 Operation description The L6924U is a fully integrated battery charger that allows a very compact battery management system for space limited applications. It integrates in a small package all the power elements: power MOSFET, reverse blocking diode and the sense resistor. It normally works as a linear charger when powered from an external voltage regulated adapter or USB port. However, thanks to its very low minimum input voltage (down to 2.5 V) the L6924U can also work as a quasi-pulse charger when powered from a current limited adapter. To work in this condition, it is enough to set the device’s charging current higher than the adapter’s one (Chapter 6.2: Quasi-pulse mode on page 14). The advantage of the linear charging approach is that the device has a direct control of the charging current and so the designer needn’t to rely on power source. However, the advantage of the quasi-pulse approach is that the power dissipated inside the portable equipment is dramatically reduced. The L6924U charges the battery in three phases: ● Pre-charge constant current: in this phase (active when the battery is deeply discharged) the battery is charged with a low current (internally set to 10 % of the fast- charge current). ● Fast-charge constant current: in this phase the device charges the battery with the maximum current (IAC for AC adapter mode, IUSB for USB mode). ● Constant voltage: when the battery voltage reaches the selected output voltage, the device starts to reduce the current, until the charge termination is done. The full flexibility is provided by: ● Programmable fast-charging current (IAC or IUSB) (Chapter 7.3 on page 18). ● Programmable end of charge current threshold (IENDTH) (Chapter 7.4 on page 20). ● Programmable end of charge timer (TMAXCH) (Chapter 7.7 on page 21). If a PTC or NTC resistor is used, the device can monitor the battery temperature in order to protect the battery from operating under unsafe thermal conditions. Beside the good thermal behavior guaranteed by low thermal resistance of the package, additional safety is provided by the built-in temperature control loop. The IC monitors continuously its junction temperature. When the temperature reaches approximately 120 °C, the thermal control loop starts working, and reduces the charging current, in order to keep the IC junction temperature at 120 °C. Two open collector outputs are available for diagnostic purpose (status pins ST1 and ST2). They can be also used to drive external LEDs or to interface with a microcontroller. The voltage across the resistor connected between IEND and GND gives information about the actual charging current (working as a gas gauge), and it can be easily fed into a microcontroller ADC. Battery disconnection control is provided thanks to the differentiated sensing and forcing output pins. A small current is sunk and forced through VOUT. If VOSNS doesn’t detect the battery, the IC goes into a standby mode. Figure 5 on page 12 shows the real charging profile of a Li-Ion battery, with a fast charge current of 450 mA (R1 or R2 = 26 kΩ). |
Nº de peça semelhante - L6924U013 |
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Descrição semelhante - L6924U013 |
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