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SMB239 Datasheet(PDF) 11 Page - Summit Microelectronics, Inc. |
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SMB239 Datasheet(HTML) 11 Page - Summit Microelectronics, Inc. |
11 / 30 page SMB239 Summit Microelectronics, Inc 2129 3.0 2/23/2009 11 APPLICATIONS INFORMATION DEVICE OPERATION The SMB239 is a fully programmable battery charger for single-cell Li-Ion and Li-Polymer battery packs. The device’s simple, linear-mode operation and ultra-small package significantly reduce component count and required board space. The SMB239 provides four main charging phases: trickle-charge, pre-conditioning (pre- charge), constant (fast-charge) current and constant voltage. The overall system accuracy of the SMB239 is 1%, allowing for a higher capacity utilization versus other conventional solutions. The main battery charging parameters are programmable, allowing for high design flexibility and sophisticated battery management. Furthermore, the SMB239 offers many advanced protection features, allowing applications to meet strict safety standards without the need for additional cost and components. Power Supply The SMB239 can be powered from an input voltage between +4.35 and +6.5 Volts applied between the IN pin and ground. The voltage on the IN pin is monitored by an Under-Voltage (UVLO) circuit, which prevents the charger from turning on when the voltage at this node is less than the UVLO threshold (+3.5V). The IN pin also supplies an internal +2.5V VDD regulator, which is used as an internal VDD supply. When the input supply is removed, the SMB239 enters a low-power shutdown mode, exhibiting a very low discharge leakage current (2µA), thereby extending battery life. Pre-qualification Mode When an external wall adaptor or another type of power source is connected, the SMB239 performs a series of pre-qualification tests before initiating the first charge cycle. The input voltage level needs to be higher than the UVLO threshold, and 130mV greater than the battery voltage; and the appropriate I2C command (enable/disable) needs to be asserted. The pre- qualification parameters are continuously monitored and charge cycle is suspended when one of them is outside the limits. A device option exists (controlled by register 08h[5]) for preventing charging initiation upon power cycling unless the battery voltage is 200mV, 390mV or 550mV (VCH) below the float voltage level. This prevents over- stressing of the battery via continuous charging cycles in systems with short run times and frequent power cycling (IN power connect/disconnect). Trickle-charge Mode Once all pre-qualification conditions are met, the device checks the battery voltage to decide if trickle-charging is required. If the battery voltage is below approximately 2.0V, a charging current of 10mA (typical) is applied on the battery cell. This allows the SMB239 to reset the protection circuit in the battery pack and bring the battery voltage to a higher level without compromising safety. Pre-charge Mode Once the battery voltage crosses the 2.0V level, the SMB239 pre-charges the battery to safely charge the deeply discharged cells (Figure 3). The pre-charge (pre-conditioning) current is programmable from 25mA to 212.5mA (Register 00h). The SMB239 remains in this mode until the battery voltage reaches the pre- charge to fast-charge voltage threshold (programmable from +2.4V to +3.1V in 100mV steps). If the pre-charge to fast-charge voltage threshold is not exceeded before the pre-charge timer expires, the charge cycle is terminated and a corresponding timeout fault signal is asserted (“Pre-charge Timeout” in register 36h). Constant Current Mode When the battery voltage exceeds the pre-charge to fast-charge voltage threshold, the device enters the constant current (fast charge) mode. During this mode, the fast charge current level is set by the corresponding register. The fast charge current is programmable from 47.5mA to 525mA (Register 00h). Constant Voltage Mode When the battery voltage reaches the pre-defined float voltage, the fast-charge current starts diminishing. The float voltage is programmable from +4.020V to +4.40V in 20mV steps and is ±1% accurate over the +10°C to +50 °C temperature range. The higher float voltage settings of the SMB239 enable the charging of modern battery packs with a required float voltage of 4.3V, and 4.4V. Furthermore, the ability to dynamically adjust the float voltage allows the implementation of sophisticated battery charging and control algorithms. Charge Completion The charge cycle is considered complete when the charge current reaches the programmed termination current threshold. The termination current is programmable from 25mA to 250mA (Register 01h). If the termination current threshold is not met before the fast-charge timer expires, the charge cycle is terminated and a corresponding timeout fault signal is asserted (“Fast-charge Timeout” in register 36h). |
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