Datasheet

LT3470A
7
3470afb
SHDN (Pin 8): The SHDN pin is used to put the LT3470A in
shutdown mode. Tie to ground to shut down the LT3470A.
Apply 2V or more for normal operation. If the shutdown
feature is not used, tie this pin to the V
IN
pin.
NC (Pin 7): This pin can be left floating, connected to V
IN
,
or tied to GND.
V
IN
(Pin 6): The V
IN
pin supplies current to the LT3470A’s
internal regulator and to the internal power switch. This
pin must be locally bypassed.
GND (Pin 5): Tie the GND pin to a local ground plane
below the LT3470A and the circuit components. Return
the feedback divider to this pin.
SW (Pin 4): The SW pin is the output of the internal power
switch. Connect this pin to the inductor, catch diode and
boost capacitor.
BOOST (Pin 3): The BOOST pin is used to provide a drive
voltage, which is higher than the input voltage, to the
internal bipolar NPN power switch.
BIAS ( Pin 2): The BIAS pin connects to the internal boost
Schottky diode and to the internal regulator. Tie to V
OUT
when V
OUT
> 2.5V or to V
IN
otherwise. When V
BIAS
> 3V
the BIAS pin will supply current to the internal regulator.
FB ( Pin 1): The LT3470A regulates its feedback pin to
1.25V. Connect the feedback resistor divider tap to this
pin. Set the output voltage according to V
OUT
= 1.25V (1
+ R1/R2) or R1 = R2 (V
OUT
/1.25 – 1).
Exposed Pad (
Pin 9): Ground. Must be soldered to PCB.
PIN FUNCTIONS
BLOCK DIAGRAM
–
+
–
+
RQʹ
SQ
500ns
ONE SHOT
V
REF
1.25V
BURST MODE
DETECT
SW
GND
3470a BD
FB
R2 R1
SHDN
ENABLE
V
IN
V
IN
NC
BIAS
BOOST
L1
C2
C3
V
OUT
g
m
C1