LTC1877 Linear Technology, LTC1877 Datasheet - Page 6

• Manufacturer Part Number: LTC1877
• Description: High Efficiency Monolithic Synchronous Step-Down Regulator
• Manufacturer: Linear Technology

FUNCTIONAL DIAGRA
LTC1877
PIN
RUN (Pin 1): Run Control Input. Forcing this pin below
0.4V shuts down the LTC1877. In shutdown all functions
are disabled drawing <1 A supply current. Forcing this pin
above 1.2V enables the LTC1877. Do not leave RUN
floating.
I
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is from 0.5V
to 1.9V.
V
from an external resistive divider across the output.
GND (Pin 4): Ground Pin.
SW (Pin 5): Switch Node Connection to Inductor. This pin
6
SYNC/MODE
TH
FB
PLL LPF
RUN
U
V
U
(Pin 2): Error Amplifier Compensation Point. The
(Pin 3): Feedback Pin. Receives the feedback voltage
8
7
3
1
FB
0.6V
FUNCTIONS
U
+
–
DEFEAT
BURST
0.8V REF
V
U
IN
SHUTDOWN
X
Y
U
0.85V
SHIFT
FREQ
VCO
Y = “0” ONLY WHEN X IS A CONSTANT “1”
V
0.8V
REF
g
m
+
–
OVDET
= 0.5m
+
–
EA
SLOPE
COMP
W
V
–
+
IN
SLEEP
OSC
V
IN
2
0.45V
I
TH
connects to the drains of the internal main and synchro-
nous power MOSFET switches.
V
to GND, Pin 4.
SYNC/MODE (Pin 7): External Clock Synchronization and
Mode Select Input. To synchronize with an external clock,
apply a clock with a frequency between 400kHz and
700kHz. To select Burst Mode operation, tie to V
ing this pin selects pulse skipping mode. Do not leave this
pin floating.
PLL LPF (Pin 8): Output of the Phase Detector and Control
Input of Oscillator. Connect a series RC lowpass network
from this pin to ground if externally synchronized. If
unused, this pin may be left open.
IN
RS LATCH
+
–
S
R
(Pin 6): Main Supply Pin. Must be closely decoupled
BURST
EN
Q
Q
SLEEP
SWITCHING
BLANKING
CIRCUIT
LOGIC
AND
0.8V
–
I
SHOOT-
COMP
THRU
ANTI
I
RCMP
+
V
+
–
IN
6
IN
. Ground-
6
5
4
1877 BD
V
SW
GND
IN