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LTC4075HVX Datasheet(PDF) 9 Page - Linear Technology |
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LTC4075HVX Datasheet(HTML) 9 Page - Linear Technology |
9 / 16 page LTC4075HVX 9 4075hvxf OPERATION The LTC4075HVX is designed to efficiently manage charg- ing of a single-cell lithium-ion battery from two separate power sources: a wall adapter and USB power bus. Us- ing 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 LTC4075HVX has two internal P-channel power MOSFETs and thermal regulation circuitry. No blocking diodes or external sense resistors are required. Power Source Selection The LTC4075HVX can charge a battery from either the wall adapter input or the USB port input. The LTC4075HVX au- tomatically senses the presence of voltage at each input. If both power sources are present, the LTC4075HVX defaults to the wall adapter source provided a valid voltage is pres- ent at the DCIN input. “Valid voltage” is defined as: • Supply voltage is greater than the undervoltage lock- out threshold and less than the overvoltage lockout threshold. • Supply voltage is greater than the battery voltage by 40mV. The open drain power status outputs (⎯P⎯W⎯R and USBPWR) indicate which power source has been selected. Table 1 describes the behavior of these status outputs. 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: R V I I V R R IDC CHRG DC CHRG DC IDC IUSB == = − − 1000 1000 , 1 1000 1000 V I I V R CHRG USB CHRG USB IUSB − − = , *Any external sources that hold the ITERM pin above 100mV will prevent the LTC4075HVX 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: I V R ch ing from wall adapter BAT IDC IDC = •, ( arg 1000 )) •, ( arg sup I V R ch ing from USB p BAT IUSB IUSB = 1000 lly) 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: R V I I V R ITERM TERMINATE TERMINATE ITERM == 100 100 , The termination condition is detected by 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 LTC4075HVX enters 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 programmed termination current. The 1.6ms filter time (tTERMINATE) on the termination comparator ensures that transient loads of this nature do not result in premature charge cycle termination. Once the average charge cur- rent drops below the programmed termination threshold, the LTC4075HVX terminates the charge cycle and stops providing current out of the BAT pin. In this state, any load on the BAT pin must be supplied by the battery. |
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