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LTC4078X Datasheet(PDF) 9 Page - Linear Technology |
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LTC4078X Datasheet(HTML) 9 Page - Linear Technology |
9 / 16 page LTC4078/LTC4078X 9 4078xfb OPERATION The LTC4078/LTC4078X are designed to efficiently man- age charging of a single-cell lithium-ion battery from two separate power sources: a wall adapter and USB power bus. Using the constant-current/constant-voltage algorithm, the charger can deliver up to 950mA of charge current from the wall adapter supply or up to 850mA of charge current from the USB supply with a final float voltage accuracy of ±0.6%. The LTC4078/LTC4078X have two internal P-chan- nel power MOSFETs and thermal regulation circuitry. No blocking diodes or external sense resistors are required. Power Source Selection The LTC4078/LTC4078X can charge a battery from ei- ther the wall adapter input or the USB port input. The LTC4078/LTC4078X automatically sense the presence of voltage at each input. If both power sources are present, the LTC4078/LTC4078X default to the wall adapter source provided a valid voltage is present at the DCIN input. “Valid voltage” is defined as: • Supply voltage is greater than the UVLO threshold and less than the OVLO threshold. • Supply voltage is greater than the battery voltage by 40mV. The open-drain power status output (PWR) indicates which power source has been selected. Table 1 describes the behavior of this status output. Programming and Monitoring Charge Current The charge current delivered to the battery from the wall adapter or USB supply is programmed using a single re- sistor from the IDC or IUSB pin to ground. Both program resistors and charge currents (ICHRG) are calculated using the following equations: RIDC = 1000V ICHRG DC ,ICHRG DC = 1000V RIDC RIUSB = 1000V ICHRG USB ,ICHRG USB = 1000V RIUSB *Any external sources that hold the ITERM pin above 100mV will prevent the LTC4078X from terminating a charge cycle. Charge current out of the BAT pin can be determined at any time by monitoring the IDC or IUSB pin voltage and applying the following equations: IBAT = VIDC RIDC • 1000, (charging from wall adapter) IBAT = VIUSB RIUSB • 1000, (charging from USBsupply) Battery Detection By default, the BATDET pin is pulled high with an internal resistor, disabling the charger. To enable the charger, the BATDET pin must be pulled below the VBDET threshold (typically 1.75V). An external resistor to ground less than 100k (typically 3.9k) located in the battery pack is used to detect battery presence. Programming Charge Termination The charge cycle terminates when the charge current falls below the programmed termination threshold level during constant-voltage mode. This threshold is set by connecting an external resistor, RITERM, from the ITERM pin to ground. The charge termination current threshold (ITERMINATE) is set by the following equation: RITERM = 100V ITERMINATE ,ITERMINATE = 100V RITERM The termination condition is detected using an internal filtered comparator to monitor the ITERM pin. When the ITERM pin voltage drops below 100mV* for longer than tTERMINATE (typically 1.6ms), charging is terminated. The charge current is latched off and the LTC4078/LTC4078X enter standby mode. When charging, transient loads on the BAT pin can cause the ITERM pin to fall below 100mV for short periods of time before the DC charge current has dropped below the |
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