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LT3755 Datasheet(PDF) 9 Page - Linear Technology |
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LT3755 Datasheet(HTML) 9 Page - Linear Technology |
9 / 26 page LT3791-1 9 37911fa For more information www.linear.com/LT3791-1 pin FuncTions CTRL(Pin1):OutputCurrentSenseThresholdAdjustment Pin. Regulating threshold V(ISP-ISN) is 1/10th of (VCTRL – 200mV). CTRL linear range is from 200mV to 1.1V. For VCTRL > 1.3V, the current sense threshold is constant at the full-scale value of 100mV. For 1.1V < VCTRL < 1.3V, the dependenceofthecurrentsensethresholduponVCTRLtran- sitions from a linear function to a constant value, reaching 98% of full scale by VCTRL = 1.2V. Connect CTRL to VREF for the 100mV default threshold. Force less than 175mV (typical) to stop switching. Do not leave this pin open. SS (Pin 2): Soft-start reduces the input power sources surge current by gradually increasing the controller’s cur- rent limit. A minimum value of 22nF is recommended on this pin. A 100k resistor must be placed between SS and VREF for the LT3791-1. PWM (Pin 3): A signal low turns off switches, idles switch- ing and disconnects the VC pin from all external loads. The PWMOUT pin follows the PWM pin. PWM has an internal 90k pull-down resistor. If not used, connect to INTVCC. C/10 (Pin 4): C/10 Charge Termination Pin. An open-drain pull-down on C/10 asserts if FB is greater than 1.15V (typi- cal) and V(ISP-ISN) is less than 10mV (typical). To function, the pin requires an external pull-up resistor. SHORT (Pin 5): Output Shorted Pin. An open-drain pull- downon SHORTassertsifFBislessthan400mV(typical). To function, the pin requires an external pull-up resistor. VREF (Pin 6): Voltage Reference Output Pin, Typically 2V. This pin drives a resistor divider for the CTRL pin, either for output current adjustment or for temperature limit/ compensation of the output load. Can supply up to 200µA of current. ISMON (Pin 7): Monitor pin that produces a voltage that is ten times the voltage V(ISP-ISN). ISMON will equal 1V when V(ISP-ISN) = 100mV. IVINMON (Pin 8): Monitor pin that produces a voltage that is twenty times the voltage V(IVINP-IVINN). IVINMON will equal 1V when V(IVINP-IVINN) = 50mV. EN/UVLO (Pin 9): Enable Control Pin. Forcing an accurate 1.2V falling threshold with an externally programmable hysteresis is generated by the external resistor divider and a 3µA pull-down current. Above the 1.2V (typical) threshold (but below 6V), EN/UVLO input bias current is sub-µA. Below the falling threshold, a 3µA pull-down cur- rent is enabled so the user can define the hysteresis with the external resistor selection. An undervoltage condition resets soft-start. Tie to 0.3V, or less, to disable the device and reduce VIN quiescent current below 1µA. IVINP (Pin 10): Positive Input for the Input Current Limit andMonitor.Inputbiascurrentforthispinistypically90µA. IVINN (Pin 11): Negative Input for the Input Current Limit and Monitor. The input bias current for this pin is typically 20µA. VIN (Pin 12): Main Input Supply. Bypass this pin to PGND with a capacitor. INTVCC (Pin 13): Internal 5V Regulator Output. The driver and control circuits are powered from this voltage. Bypass this pin to PGND with a minimum 4.7µF ceramic capacitor. TG1 (Pin 14): Top Gate Drive. Drives the top N-channel MOSFET with a voltage equal to INTVCC superimposed on the switch node voltage SW1. BST1 (Pin 15): Bootstrapped Driver Supply. The BST1 pin swings from a diode voltage below INTVCC up to a diode voltage below VIN + INTVCC. SW1 (Pin 16): Switch Node. SW1 pin swings from a diode voltage drop below ground up to VIN. PGND (Pins 17, 20): Power Ground. Connect these pins closely to the source of the bottom N-channel MOSFET. BG1 (Pin 18): Bottom Gate Drive. Drives the gate of the bottom N-channel MOSFET between ground and INTVCC. BG2 (Pin 19): Bottom Gate Drive. Drives the gate of the bottom N-channel MOSFET between ground and INTVCC. SW2 (Pin 21): Switch Node. SW2 pin swings from a diode voltage drop below ground up to VOUT. |
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