LTC1773 LINER [Linear Technology], LTC1773 Datasheet - Page 5

• Manufacturer Part Number: LTC1773
• Description: Synchronous Step-Down DC/DC Controller
• Manufacturer: LINER [Linear Technology]

PIN
FUNCTIONAL DIAGRA
I
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is 0V to 1.2V.
Under high duty cycle and nearing current limit, I
swing up to 2.4V.
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
0.8s/µF. Forcing this pin below 0.4V shuts down all the
circuitry.
SYNC/FCB (Pin 3): 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 to a resistive divider from
the secondary output. To synchronize with an external
clock, apply a TTL/CMOS compatible clock with a fre-
quency between 585kHz and 750kHz. To select Burst
Mode operation, tie SYNC/FCB to V
forces continuous operation.
TH
U
U
(Pin 1): Error Amplifier Compensation Point. The
FUNCTIONS
U
SYNC/FCB
U
V
FB
0.4µA
3
4
U
0.6V
SHUTDOWN
–
+
TRIP = 2.5V
DEFEAT
0.8V REF
SYNC
UVLO
DEFEAT
BURST
X
0.8V
IN
W
Y
RUN/SS
. Grounding this pin
–
+
SHIFT
2
FREQ
OSC
1.5µA
FCB
0.86V
0.8V
Y = “0” ONLY WHEN X IS A CONSTANT “1”
+
+
–
–
SOFT-START
RUN/SOFT
OVDET
START
RUN/
EA
SLOPE
COMP
TH
–
+
can
Figure 2.
V
from an external resistive divider across the output. Do not
use more than 0.01µF of feedforward capacitance from FB
to the output.
GND (Pin 5): Ground Pin.
BG (Pin 6): Bottom Gate Driver of External N-Channel
Power MOSFET. This pin swings from 0V to V
TG (Pin 7): Top Gate Driver of External P-Channel Power
MOSFET. This pin swings from 0V to V
V
to GND (pin 5).
SENSE
parator. A sense resistor between this pin and V
peak current in the top switch. Connect this pin to the
source of the external P-Channel power MOSFET.
SW (Pin 10): Switch Node Connection to Inductor. This
pin connects to the drains of the external main and
synchronous power MOSFET switches.
0.22V
I
FB
IN
TH
1
(Pin 8) : Main Supply Pin. Must be closely decoupled
(Pin 4): Feedback Pin. Receives the feedback voltage
–
S
R
(Pin 9): The Negative Input to the Current Com-
+
–
Q
Q
50mV
BURST
COMP
EN
SWITCHING
BLANKING
SLEEP
CIRCUIT
LOGIC
AND
0.4V
SHOOT-THRU
–
I
I
COMP
ANTI
RCMP
+
+
–
IN
LTC1773
10
8
9
7
6
5
.
1773 FD
V
SENSE
TG
BG
SW
GND
IN
–
IN
IN
.
sets the
1773fb
5