Datasheet

LT1912
7
1912fa
BD (Pin 1): This pin connects to the anode of the boost
Schottky diode. BD also supplies current to the internal
regulator.
BOOST (Pin 2): This pin is used to provide a drive
voltage, higher than the input voltage, to the internal bipolar
NPN power switch.
SW (Pin 3): The SW pin is the output of the internal power
switch. Connect this pin to the inductor, catch diode and
boost capacitor.
V
IN
(Pin 4): The V
IN
pin supplies current to the LT1912’s
internal regulator and to the internal power switch. This
pin must be locally bypassed.
RUN/SS (Pin 5): The RUN/SS pin is used to put the
LT1912 in shutdown mode. Tie to ground to shut down
the LT1912. Tie to 2.5V or more for normal operation. If
the shutdown feature is not used, tie this pin to the V
IN
pin. RUN/SS also provides a soft-start function; see the
Applications Information section.
SYNC (Pin 6): This is the external clock synchronization
input. Ground this pin when SYNC function is not used. Tie
to a clock source for synchronization. Clock edges should
have rise and fall times faster than 1µs. See synchronizing
section in Applications Information.
N/C (Pin 7): This pin should be tied to ground.
FB (Pin 8): The LT1912 regulates the FB pin to 0.790V.
Connect the feedback resistor divider tap to this pin.
V
C
(Pin 9): The V
C
pin is the output of the internal error
amplifier. The voltage on this pin controls the peak switch
current. Tie an RC network from this pin to ground to
compensate the control loop.
R
T
(Pin 10): Oscillator Resistor Input. Connecting a resis-
tor to ground from this pin sets the switching frequency.
GND (Exposed Pad Pin 11): Ground. The exposed pad
must be soldered to PCB.
+
–
+
–
OSCILLATOR
200kHz–500kHz
V
C
CLAMP
SOFT-START
SLOPE COMP
R
V
IN
V
IN
RUN/SS
BOOST
SW
SWITCH
LATCH
V
C
V
OUT
C2
C3
C
F
L1
D1
C
C
R
C
BD
R
T
R2
GND
ERROR AMP
R1
FB
R
T
C1
S
Q
∑
1912 BD
4
5
10
1
2
3
9
11 8
6
INTERNAL 0.79V REF
SYNC
PIN FUNCTIONS
BLOCK DIAGRAM