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SC810ULTRT Datasheet(PDF) 10 Page - Semtech Corporation |
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SC810ULTRT Datasheet(HTML) 10 Page - Semtech Corporation |
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10 / 19 page  © 2008 Semtech Corporation SC810 10 Charger Operation The SC810 is a single cell Li-ion battery charger. It imple- ments a Constant Current, Constant Voltage, Constant Temperature (CC/CV/CT) charging algorithm. When an input supply is first detected, a charge cycle is initiated and the STATB open-drain output goes low. If the battery voltage is less than the pre-charge threshold voltage, the pre-charge current is supplied. Pre-charge current is 20% of the programmed fast-charge current. When the battery voltage exceeds the pre-charge thresh- old, typically within seconds for a standard battery with a starting cell voltage greater than 2V, the fast-charge Constant Current (CC) mode begins. The charge current soft-starts in three steps (20%, 60%, and 100% of pro- grammed fast-charge current) to reduce adapter load transients. CC current is programmed by the IPRGM resis- tance to ground. The charger begins Constant Voltage (CV) regulation when the battery voltage rises to the fully-charged single- cell Li-ion regulation voltage (V CV ), nominally 4.2V. In CV regulation, the output voltage is regulated, and as the battery charges, the charge current gradually decreases. The STATB output goes high when I BAT drops below the termination current threshold, which is 10% of the IPRGM pin programmed fast-charge current, regardless of the mode selected. This is known as charge termination. Optional Float-charging or Monitoring Depending on the state of the ENB input, upon termina- tion the SC810 either operates indefinitely as a voltage regulator (float-charging) or it turns off its output. If the output is turned off upon termination, the device enters the monitor state. In this state, the output remains off until the BAT pin voltage decreases by the re-charge threshold (VT ReQ). A re-charge cycle then begins automati- cally and the process repeats. A forced re-charge cycle can also be periodically commanded by the processor to keep the battery topped-off without float-charging. See the Monitor State section for details. Re-charge cycles are not indicated by the STATB pin. Charging Input Pin Properties Glitch filtering is performed on the VIN pin, so an input voltage that is ringing across its Under-Voltage Lockout (UVLO) threshold will not be recognized until the ringing has ceased. The UVLO rising threshold is set higher than the voltage of a fully charged Li-ion single cell battery, ensuring that only a charging source capable of fully charging the battery has been applied. If the charging current loads the adapter beyond its current limit, the input voltage will be pulled down to just above the battery voltage. The UVLO falling threshold is set close to the battery voltage pre-charge threshold to permit low- dissipation charging from a current limited adapter. Constant Current Mode Fast-charge Current Programming The Constant Current (CC) mode is active when the battery voltage is above VT PreQ and less than VCV. The pro- grammed CC regulation fast-charge (FQ) current is inversely proportional to the resistance between IPRGM and GND according to the equation 1000 R V I IPRGM Typ _ IPRGM FQ The fast-charge current can be programmed for a minimum of 70mA and a maximum of 995mA, nominally. Current regulation accuracy is dominated by gain error at high current settings, and offset error at low current set- tings. The range of expected fast-charge output current versus programming resistance is shown in Figures 1a and 1b. The figures show the nominal current versus nominal R IPRGM resistance as the center plot and two theo- retical limit plots indicating maximum and minimum current versus nominal programming resistance. These plots are derived from models of the expected worst-case contribution of error sources depending on programmed current. The current range includes the uncertainty due to 1% tolerance resistors. The dots on each plot indicate the currents obtained with standard value 1% tolerance resistors. Figures 1a and 1b show low and high resistance ranges, respectively. Pre-charge Mode This mode is automatically enabled when the battery voltage is below the pre-charge threshold voltage (VT PreQ), typically 2.8V. Pre-charge current conditions the battery for fast charging. The pre-charge current value is Applications Information |
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