LT3755/LT3755-1/LT3755-2 PIN FUNCTIONS (MSOP/QFN)RT (Pin 11/Pin 5): Switching Frequency Adjustment Pin. VIN (Pin 14/Pin 8): Input Supply Pin. Must be locally Set the frequency using a resistor to GND (for resistor bypassed with a 0.22µF (or larger) capacitor placed close values, see the Typical Performance curve or Table 1). Do to the IC. not leave the RT pin open. SENSE (Pin 15/Pin 9): The current sense input for the SHDN/UVLO (Pin 12/Pin 6): Shutdown and Undervoltage control loop. Kelvin connect this pin to the positive ter- Detect Pin. An accurate 1.22V falling threshold with ex- minal of the switch current sense resistor, RSENSE, in the ternally programmable hysteresis detects when power is source of the NFET. The negative terminal of the current OK to enable switching. Rising hysteresis is generated sense resistor should be Kelvin connected to the GND by the external resistor divider and an accurate internal plane of the IC. 2.1µA pull-down current. Above the threshold (but below 6V), SHDN/UVLO input bias current is sub-µA. Below the GATE (Pin 16/Pin 10): N-channel FET Gate Driver Output. falling threshold, a 2.1µA pull-down current is enabled so Switches between INTVCC and GND. Driven to GND during the user can define the hysteresis with the external resistor shutdown, fault or idle states. selection. An undervoltage condition resets soft-start. Exposed Pad (Pin 17/Pin 17): Ground. This pin also serves Tie to 0.4V, or less, to disable the device and reduce VIN as current sense input for control loop, sensing negative quiescent current below 1µA. terminal of current sense resistor. Solder the Exposed Pad INTV directly to ground plane. CC (Pin 13/Pin 7): Regulated Supply for Internal Loads, GATE Driver and PWMOUT Driver. Supplied from VIN and regulates to 7.15V (typical). INTVCC must be bypassed with a 4.7µF capacitor placed close to the pin. Connect INTVCC directly to VIN if VIN is always less than or equal to 8V. Rev. E 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts
