Datasheet

7
LT1680
RUN/SHDN (Pin 11): Precision Referenced Shutdown.
Can be used as logic level input for shutdown control or
as an analog monitor for input supply undervoltage
protection, etc. IC is enabled when RUN/SHDN pin rising
edge exceeds 1.25V. 25mV of hysteresis helps assure
stable mode switching. All internal functions are disabled
in shutdown mode. If this function is not desired, connect
RUN/SHDN to 12V
IN
(typically through a 100k resistor).
See Applications Information.
PGND (Pin 12): Power Ground. References the output
switch and internal driver control circuits. Connect with
low impedance trace to V
IN
decoupling capacitor negative
(ground) terminal.
GATE (Pin 13): Driver Output. Connect to gate of external
power FET switch.
12V
IN
(Pin 14): 12V Power Supply Input. Bypass with at
least 1µF to PGND.
SYNC (Pin 15): Oscillator Synchronization Pin with
TTL-Level Compatible Input. Input drives internal rising
edge triggered one shot; SYNC signal on/off times should
be ≥1µs (10% to 90% duty cycle at 100kHz). Does not
contain internal pull-up. Connect to SGND if not used.
5V
REF
(Pin 16): 5V Reference Output. Allows connection
of external loads up to 10mA DC. Reference is not available
during shutdown. Typically bypassed with at least 1µF
capacitor to SGND.
REFERENCE ONE SHOT
–
1.25V
Q
UVLO
CIRCUIT
SR
5V
REF
5V
SYNC
GATE
SENSE
+
SENSE
–
I
AVG
V
IN
V
OUT
R
SENSE
12V
IN
PGND
SGND
OSC
C
T
R
CT
C
CT
V
C
SL/ADJ
V
REF
V
FB
–
+
–
+
IC1
–
+
2.5V
1680 BD
–
+
EA
0.5µA
CURRENT
SENSE
AMPLIFIER
SS
1.25V
CIRCUIT
ENABLE
RUN/SHDN
+
RUN SHDN
8µA
SOFT START
12V
–
+
×15
V
OUT
UU
U
PI FU CTIO S
BLOCK DIAGRA
W