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LTC4040 Datasheet(PDF) 10 Page - Linear Technology |
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LTC4040 Datasheet(HTML) 10 Page - Linear Technology |
10 / 26 page LTC4040 10 4040fa For more information www.linear.com/LTC4040 pin FuncTions VSYS (Pins 1, 24): System Voltage Output Pin. This pin is used to provide power to an external load from either the primary input supply or the backup battery if the primary inputsupplyisnotavailable.Inadditiontosupplyingpower to the load, this pin provides power to charge the battery when input power is available. VSYS should be bypassed with a low ESR ceramic capacitor of at least 100µF to GND. PROG (Pin 2): Charge Current Program Pin. An external resistor from the PROG pin to ground programs the full- scale charge current. At full scale, the PROG pin servos to 0.8V. The ratio of BAT pin current to PROG pin current is internally set to 2500. CLPROG (Pin 3): VSYS Current Monitoring Pin. The ratio betweentheCLPROGpinvoltageandthedifferentialvoltage between VINandCLNisinternallysetto32.Chargecurrent is reduced when the CLPROG pin voltage reaches 0.8V. CHGOFF (Pin 4): Disable Pin for the Battery Charger. Tie this pin to GND to enable the charger or to a voltage above 1.2V to disable it. Do not leave this pin unconnected. BSTOFF (Pin 5): Disable Pin for the Backup Boost Con- verter. Tie this pin to GND to enable the boost backup or to a voltage above 1.2V to disable backup. Do not leave this pin unconnected. VIN (Pin 6): Input Pin. Power can be applied directly to this pin if the optional overvoltage protection (OVP) fea- ture is not used. For applications where the OVP feature is required, connect an external N-channel FET between the power supply output VPWR and this pin. CLN (Pin 7): Negative terminal pin for an external cur- rent limit sense resistor connected between VIN and this pin. This resistor is used to monitor the current from VIN to VSYS. The LT4040 reduces charge current in order to maintain25mVacrossthissenseresistor.However,itdoes not limit the system current if the drop exceeds 25mV. CHRG (Pin 8): Open-Drain Charge Status Output; typi- cally pulled up through a resistor to a reference voltage. During a battery charging cycle, CHRG is pulled low until the charge current drops below C/8 when the CHRG pin becomes high impedance. FAULT (Pin 9): Open-Drain Fault Status Output; typically pulled up through a resistor to a reference voltage. This pin indicates charge cycle fault conditions during a battery charging cycle. A temperature fault or a bad-battery fault causes this pin to be pulled low. If no fault conditions exist, the FAULT pin remains high impedance. RSTFB (Pin 10): Reset Comparator Input. High Imped- ance input to an accurate comparator with a 0.74V falling threshold and 20mV hysteresis. This pin controls the state of the RST output pin. An external resistor divider is used betweenVSYS,RSTFBandGND.Itcanbethesameresistor divider as the BSTFB divider to monitor the system output voltage VSYS. See the Applications Information section. RST (Pin 11): Open-Drain Status Output of the Reset Comparator. This pin is pulled to ground by an internal N-channel MOSFET whenever the RSTFB pin falls below 0.74V. Once the RSTFB pin voltage recovers, the pin be- comes high impedance after a 232ms delay. F2 (Pin 12): Logic Input to Select Battery Chemistry. A logic high on this pin selects Li-Ion and a logic low selects LiFePO4. Do not leave this pin unconnected. F1, F0 (Pins 13, 14): Logic inputs to select one of the four possible charge voltage settings for each battery chemistry. Do not leave these pins unconnected. F0 F1 F2 = 1: Li-Ion (V) F2 = 0: LiFePO4 (V) 0 0 3.95 3.45 1 0 4.00 3.50 0 1 4.05 3.55 1 1 4.10 3.60 IGATE (Pin 15): Gate Pin for the External N-Channel FETs. This pin is driven by an internal charge pump to develop sufficient overdrive to fully enhance the pass transistors. The first pass transistor is connected between the supply output VPWR and VIN and is part of the optional overvolt- age protection module. The second pass transistor, con- nected between VIN and VSYS, is mandatory and is used to disconnect the system from the input supply during backup mode. |
Similar Part No. - LTC4040_15 |
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Similar Description - LTC4040_15 |
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