LT3795 PIN FUNCTIONS RAMP (Pin 13): The RAMP pin is used for spread spectrum INTVCC (Pin 20): Regulated Supply for Internal Loads frequency modulation. The internal switching frequency and GATE Driver. Supplied from VIN and regulates to 7.7V is spread out to 70% of the original value, where the (typical). INTVCC must be bypassed with a 4.7μF capacitor modulation frequency is set by 12µA/(2 • 1V • CRAMP). If placed close to the pin. Connect INTVCC directly to VIN if not used, tie this pin to GND. VIN is always less than or equal to 8V. PWM (Pin 14): PWM Input Signal Pin. A low signal turns VIN (Pin 23): Input Supply Pin. Must be locally bypassed off switching, idles the oscillator, disconnects the VC pin with a 0.22μF (or larger) capacitor placed close to the IC. from all internal loads, and drives TG to the ISP level. EN/UVLO (Pin 24): Enable and Undervoltage Lockout PWM has an internal 500k pull-down resistor. If not used, Pin. An accurate 1.22V falling threshold with externally connect to VREF. programmable hysteresis detects when power is OK to SHORTLED (Pin 15): An open-collector pull-down on enable switching. Rising hysteresis is generated by the SHORTLED asserts when any of the following conditions external resistor divider and an accurate internal 3μA happen: pull-down current. Above the threshold, EN/UVLO input 1. FB < 0.3V after SS pin reaches 1.7V at start-up. bias current is sub-μA. Below the falling threshold, a 3μA pull-down current is enabled so the user can define the 2. LED overcurrent (V(ISP-ISN) > 375mV). hysteresis with the external resistor selection. An under- To function, the pin requires an external pull-up resistor. voltage condition resets soft-start. Tie to 0.4V, or less, to SHORTLED status is only updated during PWM high state disable the device. and latched during PWM low state. SHORTLED remains OVLO (Pin 25): Input Overvoltage Lockout Pin. An ac- asserted until the SS pin is discharged below 0.2V. curate 1.25V rising threshold detects when power is OK OPENLED (Pin 16): An open-collector pull-down on to enable switching. OPENLED asserts if the FB input is above 1.20V (typical), IVINN (Pin 26): Connection Point for the Negative Terminal and V(ISP-ISN) is less than 25mV (typical). To function, the of the Input Current Sense Resistor (RINSNS). The input pin requires an external pull-up resistor. OPENLED status current can be programmed by IIN = 60mV/RINSNS. is updated only during PWM high state and latched during PWM low state. IVINP (Pin 27): Connection Point for the Positive Terminal of the Input Current Sense Resistor. SENSE (Pin 18): The current sense input for the control loop. Kelvin connect this pin to the positive terminal of IVINCOMP (Pin 28): Input Current Sense Amplifier Output the switch current sense resistor, R Pin. The voltage at IVINCOMP pin is proportional to IIN as SENSE, in the source of the N-channel MOSFET. The negative terminal of the VIVINCOMP = IIN • RINSNS • 20. A 10nF or larger capacitor current sense resistor should be Kelvin connected to the to GND is required at this pin to compensate the input GND plane of the IC. current loop. Do not leave this pin open, and do not load this pin with a current. GATE (Pin 19): N-Channel MOSFET Gate Driver Output. Switches between INTVCC and GND. It is driven to GND during shutdown, fault or idle states. 3795fc 10 For more information www.linear.com/LT3795 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
