LTC1627 Linear Technology, LTC1627 Datasheet - Page 5

• Manufacturer Part Number: LTC1627
• Description: Monolithic Synchronous Step-Down Switching Regulator
• Manufacturer: Linear Technology

FUNCTIONAL DIAGRA
PIN
I
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/ F. Forcing this pin below 0.4V shuts down all the
circuitry.
V
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.
SYNC/FCB
TH
FB
V
8
3
U
FB
SHUTDOWN
U
(Pin 1): Error Amplifier Compensation Point. The
(Pin 3): Feedback Pin. Receives the feedback voltage
0.6V
TRIP = 2.5V
FUNCTIONS
UVLO
0.8V
REF
V
V
IN
IN
1.5 A
U
–
+
U
DEFEAT
BURST
X
0.8V
Y
U
RUN/SS
V
IN
Y = “0” ONLY WHEN X IS A CONSTANT “1”
SHIFT
FREQ
OSC
–
+
FCB
2.25 A
2
0.86V
0.8V
SLOPE
COMP
W
+
–
+
–
OVDET
RUN/SOFT
EA
START
–
+
I
TH
1
0.12V
–
+
BURST
V
to GND, Pin 4.
V
bootstrapped to go below ground to improve efficiency at
low V
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
continuous operation (see Applications Information).
S
R
EN
IN
DR
Q
Q
(Pin 6): Main Supply Pin. Must be closely decoupled
(Pin 7): Top Driver Return Pin. This pin can be
IN
SLEEP
V
(see Applications Information).
SWITCHING
BLANKING
IN
CIRCUIT
LOGIC
AND
0.4V
V
SHOOT-THRU
IN
–
I
COMP
ANTI-
I
RCMP
+
+
–
IN
. Grounding Pin 8 forces
6
LTC1627
7
5
4
1627 BD
6
5
V
SW
GND
DR
V
IN