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LTC4077 Datasheet(PDF) 9 Page - Linear Technology |
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LTC4077 Datasheet(HTML) 9 Page - Linear Technology |
9 / 16 page LTC4077 9 4077fa The LTC4077 is designed to efficiently manage 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 650mA of charge current from the USB supply with a final float voltage accuracy of ±0.6%. The LTC4077 has two internal P-channel power MOSFETs and thermal regulation circuitry. No blocking diodes or external sense resistors are required. Power Source Selection The LTC4077 can charge a battery from either the wall adapterinputortheUSBportinput.TheLTC4077automati- cally senses the presence of voltage at each input. If both power sources are present, the LTC4077 defaults to the wall adapter source provided sufficient power is present at the DCIN input. “Sufficient power” is defined as: • Supply voltage is greater than the UVLO threshold. • Supply voltage is greater than the battery voltage by 50mV (180mV rising, 50mV falling). The open drain power status output (PWR) indicates that sufficientpowerisavailable.Table1describesthebehavior of this status output. Table 1. Power Source Selection VUSBIN > 3.95V and VUSBIN < 3.95V or VUSBIN > BAT + 50mV VUSBIN < BAT + 50mV VDCIN > 4.15V and Device powered from Device powered from VDCIN > BAT + 50mV wall adapter source; wall adapter source USBIN current < 25µA PWR: LOW PWR: LOW VDCIN < 4.15V or Device powered from No charging VDCIN < BAT + 50mV USB source; PWR: LOW PWR: Hi-Z Programming and Monitoring Charge Current The charge current delivered to the battery from the wall adaptersupplyisprogrammedusingasingleresistorfrom the IDC pin to ground. Likewise, the charge current from the USB supply is programmed using a single resistor from the IUSB pin to ground if HPWR is set on its high logic state or from the IUSBL pin to ground if HPWR is set on its low logic state or it is left floating. The program resistor and the charge current (ICHRG) are calculated using the following equations: R V I I V R R IDC CHRG DC CHRG DC IDC IUS = = 1000 1000 ( ) ( ) , BB CHRG USB CHRG USB IUSB IU V I I V R R = = 1000 1000 ( ) ( ) , SSBL CHRG USB CHRG USB IUSBL V I I V R = = 200 200 ( ) ( ) , Charge current out of the BAT pin can be determined at any time by monitoring the IDC or IUSB pin voltage and using the following equations: I V R ch ing from wall adapter BAT IDC IDC = • , ( arg 1000 )) • , ( I V R BAT IUSB IUSB = 1000 charging from USB supplly HPWR chargi , ) • , ( = = high I V R BAT IUSBL IUSBL 200 nng from USB supply, ) HPWR low = OPERATIO |
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