LTC3803-3
6
38033fd
PIN FUNCTIONS
BLOCK DIAGRAM
I
TH
/RUN (Pin 1): This pin performs two functions. It
serves as the error amplifi er compensation point as well
as the run/shutdown control input. Nominal voltage range
is 0.7V to 1.9V. Forcing this pin below the shutdown
threshold (V
ITHSHDN
) causes the LTC3803-3 to shut down.
In shutdown mode, the NGATE pin is held low.
GND (Pin 2): Ground Pin.
V
FB
(Pin 3): Receives the feedback voltage from an external
resistive divider across the output.
SENSE (Pin 4): This pin performs two functions. It monitors
switch current by reading the voltage across an external
current sense resistor to ground. It also injects a current
ramp that develops slope compensation voltage across
an optional external programming resistor.
V
CC
(Pin 5): Supply Pin. Must be closely decoupled to
GND (Pin 2).
NGATE (Pin 6): Gate Drive for the External N-Channel
MOSFET. This pin swings from 0V to V
CC
.
–
+
–
+
SLOPE
COMP
CURRENT
RAMP
V
CC
GATE
DRIVER
NGATE
4
SENSE
38033 BD
300kHz
OSCILLATOR
UNDERVOLTAGE
LOCKOUT
Q
R
CURRENT
COMPARATOR
SHUTDOWN
COMPARATOR
SHUTDOWN
S
20mV
I
TH
/RUN
ERROR
AMPLIFIER
V
FB
SOFT-
START
CLAMP
V
CC
SHUNT
REGULATOR
SWITCHING
LOGIC AND
BLANKING
CIRCUIT
6
0.28V
V
CC
< V
TURNON
0.3μA
V
CC
–
+
5
3
GND
1.2V
2
1
800mV
REFERENCE
