Datasheet LT1933 (Analog Devices) - 6

LT1933
PIN FUNCTIONS (SOT-23/DFN) BOOST (Pin 1):
The BOOST pin is used to provide a drive
SHDN (Pin 4):
The SHDN pin is used to put the LT1933 in voltage, higher than the input voltage, to the internal bipolar shutdown mode. Tie to ground to shut down the LT1933. NPN power switch. Tie to 2.3V or more for normal operation. If the shutdown feature is not used, tie this pin to the V
GND (Pin 2/Pin 5 and Exposed Pad, Pin 7):
Tie the IN pin. SHDN also provides a soft-start function; see the Applications Infor- GND pin to a local ground plane below the LT1933 and mation section. the circuit components. Return the feedback divider to this pin.
VIN (Pin 5/Pin 2):
The VIN pin supplies current to the LT1933’s internal regulator and to the internal power
FB (Pin 3/Pin 6):
The LT1933 regulates its feedback pin to switch. This pin must be locally bypassed. 1.245V. Connect the feedback resistor divider tap to this pin. Set the output voltage according to VOUT = 1.245V
SW (Pin 6):
The SW pin is the output of the internal power (1 + R1/R2). A good value for R2 is 10k. switch. Connect this pin to the inductor, catch diode and boost capacitor.
BLOCK DIAGRAM
VIN VIN C2 INT REG AND UVLO D2 Σ BOOST ON OFF SLOPE R R3 COMP Q SHDN C3 S Q DRIVER Q1 C4 L1 OSC SW VOUT C1 D1 FREQUENCY FOLDBACK VC gm 1.245V GND FB R2 R1 1933 BD 1933fe 6