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LTC4069EDC-TRPBF Datasheet(PDF) 11 Page - Linear Technology |
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LTC4069EDC-TRPBF Datasheet(HTML) 11 Page - Linear Technology |
11 / 16 page LTC4069 11 4069fb OPERATION 4069 F03 RNOM RNTC VCC – + TOO COLD TOO HOT NTC_ENABLE 0.76 • VCC 0.35 • VCC 0.016 • VCC 6 NTC APPLICATIONS INFORMATION Figure 3. NTC Circuit Information Undervoltage Charge Current Limiting (UVCL) The LTC4069 includes undervoltage charge (ΔVUVCL1) current limiting that prevents full charge current until the input supply voltage exceeds approximately 200mV above the battery voltage. This feature is particularly useful if the LTC4069 is powered from a supply with long leads (or any relatively high output impedance). For example, USB-powered systems tend to have highly variable source impedances (due primarily to cable quality and length). A transient load combined with such impedance can easily trip the UVLO threshold and turn the charger off unless undervoltage charge current limiting is implemented. Consider a situation where the LTC4069 is operating under normal conditions and the input supply voltage begins to droop (e.g., an external load drags the input supply down). If the input voltage reaches VBAT + ΔVUVCL1(approximately 220mV above the battery voltage), undervoltage charge current limiting will begin to reduce the charge current in an attempt to maintain ΔVUVCL1 between the VCC input and the BAT output of the IC. The LTC4069 will continue to operate at the reduced charge current until the input supply voltage is increased or constant voltage mode reduces the charge current further. Operation from Current Limited Wall Adapter By using a current limited wall adapter as the input supply, the LTC4069 dissipates significantly less power when programmed for a current higher than the limit of the supply as compared to using a non-current limited supply at the same charge current. Consider a situation where an application demands a 600mA charge current for an 800mAh Li-Ion battery. If a typical 5V (non-current limited) input supply is used, the charger’s peak power dissipation can exceed 1W. Now consider the same scenario, but with a 5V input supply with a 600mA current limit. To take advantage of the current limited supply, it is necessary to program the LTC4069 to charge at a current above 600mA. Assume that the LTC4069 is programmed for 750mA (i.e., RPROG = 1.33k) to ensure that part tolerances maintain a programmed current higher than 600mA. Since the |
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