Datasheet

5
LTC1707
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 the
LTC1707.
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.
SYNC/MODE (Pin 7): This pin performs two functions:
1) synchronize with an external clock and 2) select be-
tween two modes of low load current operation. To
synchronize with an external clock, apply a TTL/CMOS
compatible clock with a frequency between 385kHz and
550kHz. To select Burst Mode operation, float the pin or
tie it to V
IN
. Grounding Pin 7 forces pulse skipping mode
operation.
V
REF
(Pin 8): The Output of a 1.19V ±1% Precision
Reference. May be loaded up to 100µA and is stable with
up to 2000pF load capacitance.
V
FB
V
IN
3
V
REF
2
1
6
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/MODE
Y = “0” ONLY WHEN X IS A CONSTANT “1”
SHUTDOWN
SLEEP
6Ω
1.5µA
2.25µA
V
IN
V
IN
V
IN
V
IN
SW
GND
1707 BD
V
IN
BURST
EN
7
OSC
FREQ
SHIFT
1.19V
REF
UVLO
TRIP = 2.7V
Y
X
BURST
DEFEAT
SLOPE
COMP
–
+
OVDET
–
+
–
+
–
+
–
+
–
+
EA
I
COMP
–
+
I
RCMP
RUN/SOFT
START
ANTI-
SHOOT-THRU
8
UU
U
PI FU CTIO S
FU CTIO AL DIAGRA
U
U
W