Datasheet LT3575 (Analog Devices) - 5

LT3575
PIN FUNCTIONS NC (Pins 1, 15, 16)
: No Connect Pins. Can be left open of the switch. or connected to any ground plane.
VC (Pin 9)
: Compensation Pin for Internal Error Amplifi er.
VIN (Pin 2)
: Input Voltage. This pin supplies current to Connect a series RC from this pin to ground to compensate the internal start-up circuitry and as a reference voltage the switching regulator. A 100pF capacitor in parallel helps for the DCM comparator and feedback circuitry. This pin eliminate noise. must be locally bypassed with a capacitor.
RFB (Pin 10)
: Input Pin for External Feedback Resistor. This
SW (Pins 3, 4)
: Collector Node of the Output Switch. This pin is connected to the transformer primary (VSW). The pin has large currents fl owing through it. Keep the traces to ratio of this resistor to the RREF resistor, times the internal the switching components as short as possible to minimize bandgap reference, determines the output voltage (plus electromagnetic radiation and voltage spikes. the effect of any non-unity transformer turns ratio). The average current through this resistor during the fl yback
BIAS (Pin 5)
: Bias Voltage. This pin supplies current to the period should be approximately 200μA. For nonisolated switch driver and internal circuitry of the LT3575. This pin applications, this pin should be connected to V must be locally bypassed with a capacitor. This pin may IN. also be connected to VIN if a third winding is not used and if
RREF (Pin 11)
: Input Pin for External Ground-Referred VIN ≤ 15V. If a third winding is used, the BIAS voltage should Reference Resistor. This resistor should be in the range of be lower than the input voltage for proper operation. 6k, but for convenience, need not be precisely this value.
SHDN
For nonisolated applications, a traditional resistor voltage
/UVLO (Pin 6)
: Shutdown/Undervoltage Lockout. divider may be connected to this pin. A resistor divider connected to VIN is tied to this pin to program the minimum input voltage at which the LT3575
TC (Pin 12)
: Output Voltage Temperature Compensation. will operate. At a voltage below ~0.7V, the part draws no Connect a resistor to ground to produce a current quiescent current. When below 1.22V and above ~0.7V, proportional to absolute temperature to be sourced into the part will draw 7μA of current, but internal circuitry will the RREF node. ITC = 0.55V/RTC. remain off. Above 1.22V, the internal circuitry will start
TEST (Pin 13):
This pin is used for testing purposes only and a 7μA current will be fed into the SS pin. When this and must be connected to ground for the part to operate pin falls below 1.22V, 2.8μA will be pulled from the pin to properly. provide programmable hysteresis for UVLO.
GND (Pin 14, Exposed Pad Pin 17):
Ground. The exposed
SS (Pin 7)
: Soft-Start Pin. Place a soft-start capacitor pad of the package provides both electrical contact to here to limit start-up inrush current and output voltage ground and good thermal contact to the printed circuit ramp rate. Switching starts when the voltage at this pin board. The exposed pad must be soldered to the circuit reaches ~0.7V. board for proper operation and should be well connected
RILIM (Pin 8)
: Maximum Current Limit Adjust Pin. A resistor with many vias to an internal ground plane. should be tied to this pin to ground to set the current limit. Use a 10k resistor for the full current capabilities 3575f 5