Datasheet LT3511 (Analog Devices) - 5

LT3511
PIN FUNCTIONS EN/UVLO (Pin 1):
Enable/Undervoltage Lockout. The EN/
VC (Pin 10):
Compensation Pin for Internal Error Amplifier. UVLO pin is used to start up the LT3511. Pull the pin to 0V Connect a series RC from this pin to ground to compensate to shut down the LT3511. This pin has an accurate 1.21V the switching regulator. An additional 100pF capacitor from threshold and can be used to program an undervoltage this pin to ground helps eliminate noise. lockout (UVLO) threshold using a resistor divider from
T
supply to ground. A 2.6μA pin current hysteresis allows
C (Pin 11):
Output Voltage Temperature Compensa- tion. Connect a resistor to ground to produce a current the programming of undervoltage lockout (UVLO) hys- proportional to absolute temperature to be sourced into teresis. EN/UVLO can be directly connected to VIN. If left the R open circuit the part will not power up. REF node. I
V
TC = 0.55V/RTC.
IN (Pin 3):
Input Supply Pin. This pin supplies current to the internal start-up circuitry, and serves as a reference
RREF (Pin 12):
Input Pin for External Ground-Referred voltage for the DCM comparator and feedback circuitry. Reference Resistor. The resistor at this pin should be 10k. Must be locally bypassed with a capacitor. For nonisolated applications, a traditional resistor voltage divider from V
GND (Pin 5, 8, 9):
Ground Pins. All three pins should be OUT may be connected to this pin. tied directly to the local ground plane.
RFB (Pin 14):
Input Pin for External Feedback Resistor. This pin is connected to the transformer primary (V
BIAS (Pin 6):
Bias Voltage. This pin supplies current to SW). The ratio of this resistor to the R the switch driver and internal circuitry of the LT3511. REF resistor, times the internal bandgap reference, determines the output voltage This pin may also be connected to VIN if a third winding (plus the effect of any non-unity transformer turns ratio). is not used and if VIN < 20V. The part can operate down For nonisolated applications, this pin should be connected to 4.5V when BIAS and VIN are connected together. If a to GND with a 1M resistor. third winding is used, the BIAS voltage should be lower than the input voltage and greater than 3.3V for proper
SW (Pin 16):
Switch Pin. Collector of the internal power operation. BIAS must be bypassed with a 4.7μF capacitor switch. Minimize trace area at this pin to minimize EMI placed close to the pin. and voltage spikes. 3511fc 5