Datasheet
5
LTC1627
I
TH
(Pin 1): Error Amplifier Compensation Point. The
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is 0V to 1.2V.
RUN/SS (Pin 2): Combination of Soft-Start and Run
Control Inputs. A capacitor to ground at this pin sets the
ramp time to full current output. The time is approximately
0.5s/µF. Forcing this pin below 0.4V shuts down all the
circuitry.
V
FB
(Pin 3): Feedback Pin. Receives the feedback voltage
from an external resistive divider across the output.
GND (Pin 4): Ground Pin.
SW (Pin 5): Switch Node Connection to Inductor. This pin
connects to the drains of the internal main and synchro-
nous power MOSFET switches.
V
IN
(Pin 6):
Main Supply Pin. Must be closely decoupled
to GND, Pin 4.
V
DR
(Pin 7): Top Driver Return Pin. This pin can be
bootstrapped to go below ground to improve efficiency at
low V
IN
(see Applications Information).
SYNC/FCB (Pin 8): Multifunction Pin. This pin performs
three functions: 1) secondary winding feedback input, 2)
external clock synchronization and 3) Burst Mode opera-
tion or forced continuous mode select. For secondary
winding applications connect a resistive divider from the
secondary output. To synchronize with an external clock
apply a TTL/CMOS compatible clock with a frequency
between 385kHz and 525kHz. To select Burst Mode opera-
tion, float the pin or tie it to V
IN
. Grounding Pin 8 forces
continuous operation (see Applications Information).
V
FB
V
IN
3
2
1
6
7
5
4
Q
Q
R
S
0.12V
SWITCHING
LOGIC
AND
BLANKING
CIRCUIT
0.6V
I
TH
RUN/SS
0.8V
0.4V
0.86V
SYNC/FCB
Y = “0” ONLY WHEN X IS A CONSTANT “1”
SHUTDOWN
SLEEP
6Ω
1.5µA
2.25µA
V
IN
V
IN
V
IN
V
IN
V
DR
SW
GND
1627 BD
V
IN
0.8V
BURST
EN
8
OSC
FREQ
SHIFT
0.8V
REF
UVLO
TRIP = 2.5V
Y
X
BURST
DEFEAT
SLOPE
COMP
–
+
OVDET
–
+
–
+
–
+
–
+
–
+
–
+
EA
I
COMP
–
+
I
RCMP
RUN/SOFT
START
FCB
ANTI-
SHOOT-THRU
UU
U
PI FU CTIO S
FU CTIO AL DIAGRA
U
U
W