Datasheet

LTC3621/LTC3621-2
7
3621fb
For more information www.linear.com/LTC3621
pin FuncTions
(DFN/MSOP)
block DiagraM
SW (Pin 1/Pin 1): Switch Node Connection to the Inductor
of the Step-Down Regulator.
V
IN
(Pin 2/Pin 2): Input Voltage of the Step-Down Regulator.
RUN (Pin 3/Pin 3): Logic Controlled RUN Input. Do not
leave this pin floating. Logic high activates the step-down
regulator.
FB (Pin 4/Pin 5): Feedback Input to the Error Amplifier
of the Step-Down Regulator. Connect a resistor divider
tap to this pin. The output voltage can be adjusted from
0.6V to V
IN
by:
V
OUT
= 0.6V • [1 + (R2/R1)]
For Fixed V
OUT
options, connect the FB pin directly to V
OUT
.
PGOOD (Pin 4, MSOP Package Only): V
OUT
within Regu-
lation Indicator.
INTV
CC
(Pin 5/Pin 6): Low Dropout Regulator. Bypass with
at least 1µF to Ground.
MODE/SYNC (Pin 6/Pin 7): Burst Mode Select and External
Clock Synchronization of the Step-Down Regulator. Tie
MODE/SYNC to INTV
CC
for Burst Mode operation with a
400mA peak current clamp, tie MODE/SYNC to GND for
pulse skipping operation, and tie MODE/SYNC to a volt
-
age between 1V and V
INTVCC
– 1.2V for forced continuous
mode. Furthermore, connecting MODE/SYNC to an external
clock will sync the system clock to the external clock and
put the part in forced continuous mode.
GND (Exposed Pad Pin 7/Pin 9): Ground Backplane for
Power and Signal Ground. Must be soldered to PCB ground.
SGND (Pin 8, MSOP Package Only): Signal Ground.
–
+
–
+
–
+
+
V
ERROR
AMPLIFIER
BURST
AMPLIFIER
MAIN
I-COMPARATOR
–
+
–
+
OVERCURRENT
COMPARATOR
REVERSE
COMPARATOR
0.6V
FB
ITH
MODE/SYNC
RUN
PGOOD
INTV
CC
CLK
V
IN
– 5V
SW
GND
3621 BD
V
IN
FIXED V
OUT
INTV
CC
OSCILLATOR
LDO
MS8E PACKAGE ONLY
BUCK
LOGIC
AND
GATE DRIVE
SLOPE
COMPENSATION
0.8ms
SOFT-START