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