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LTC3557 Datasheet(PDF) 10 Page - Linear Technology |
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LTC3557 Datasheet(HTML) 10 Page - Linear Technology |
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10 / 28 page  LTC3557/LTC3557-1 10 35571fc PIN FUNCTIONS VIN2 (Pin 16): Power Input for Step-Down Switching Regu- lators 2 and 3. This pin will generally be connected to VOUT. SW3 (Pin 17): Power Transmission (Switch) Pin for Step-Down Switching Regulator 3. VNTC (Pin 18): Output Bias Voltage for NTC. A resistor from this pin to the NTC pin will bias the NTC thermistor. NTC (Pin 19): The NTC pin connects to a battery’s thermistor to determine if the battery is too hot or too cold to charge. If the battery’s temperature is out of range, charging is paused until it drops back into range. A low drift bias resistor is required from VNTCtoNTCandathermistorisrequiredfrom NTC to ground. If the NTC function is not desired, the NTC pin should be grounded. PROG (Pin 20): Charge Current Program and Charge Current Monitor Pin. Connecting a resistor from PROG to ground programs the charge current: I CHG(A) = 1000V R PROG If sufficient input power is available in constant current mode, this pin servos to 1V. The voltage on this pin always represents the actual charge current. GATE (Pin 21): Ideal Diode Gate Connection. This pin controls the gate of an optional external P-channel MOSFET transistor used to supplement the internal ideal diode. The source of the P-channel MOSFET should be connected to VOUT and the drain should be connected to BAT. It is important to maintain high impedance on this pin and minimize all leakage paths. BAT (Pin 22): Single Cell Li-Ion Battery Pin. Depending on available power and load, a Li-Ion battery on BAT will either deliver system power to VOUT through the ideal diode or be charged from the battery charger. VOUT (Pin 23): Output Voltage of the PowerPath Controller and Input Voltage of the Battery Charger. The majority of the portable product should be powered from VOUT. The LTC3557/LTC3557-1 will partition the available power between the external load on VOUT and the internal battery charger. Priority is given to the external load and any extra power is used to charge the battery. An ideal diode from BAT to VOUT ensures that VOUT is powered even if the load exceeds the allotted input current from VBUS or if the VBUS power source is removed. VOUT should be bypassed with a low impedance multilayer ceramic capacitor. The total capacitance on VOUT should maintain a minimum of 5μF over operating voltage and temperature. VBUS (Pin 24): USB Input Voltage. VBUS will usually be connected to the USB port of a computer or a DC output wall adapter. VBUS should be bypassed with a low impedance multilayer ceramic capacitor. ACPR (Pin 25): Wall Adapter Present Output (Active Low). A low on this pin indicates that the wall adapter input comparator has had its input pulled above its input threshold (typically 4.3V). This pin can be used to drive the gate of an external P-channel MOSFET to provide power to VOUT from a power source other than a USB port. VC (Pin 26): High Voltage Buck Regulator Control Pin. This pin can be used to drive the VC pin of an approved external highvoltagebuckswitchingregulator.AnexternalP-channel MOSFET is required to provide power to VOUT with its gate tied to the ACPR pin. The VC pin is designed to work with the LT ®3480, LT3481 and LT3505. CLPROG (Pin 27): Input Current Program and Input Current Monitor Pin. A resistor from CLPROG to ground determines the upper limit of the current drawn from the VBUS pin (i.e., the input current limit). A precise fraction of the input current, hCLPROG, is sent to the CLPROG pin. The input PowerPath delivers current until the CLPROG pin reaches 2.0V (10x Mode), 1.0V (5x Mode) or 0.2V (1x Mode). Therefore, the current drawn from VBUS will be limited to an amount given by hCLPROGandRCLPROG.InUSBapplications the resistor RCLPROG should be set to no less than 2.1k. CHRG (Pin 28): Open-Drain Charge Status Output. The CHRG pin indicates the status of the battery charger. Four possible states are represented by CHRG: charging, not charging (i.e., float charge current less than 1/10th programmed charge current), unresponsive battery (i.e., its voltage remains below 2.8V after 1/2 hour of charging) and battery temperature out of range. CHRG requires a pull-up resistor and/or LED to provide indication. Exposed Pad (Pin 29): Ground. The exposed package pad is ground and must be soldered to the PC board for proper functionality and for maximum heat transfer. |
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Similar Description - LTC3557 |
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