LTC3803-3 Datasheet, PDF (6/16 Pages) Linear Technology – Constant Frequency Current Mode Flyback DC/DC Controller in ThinSOT

LTC3803-3
PI FU CTIO S
I_TH/RUN (Pin 1): This pin performs two functions. It
serves as the error amplifier compensation point as well as
the run/shutdown control input. Nominal voltage range is
0.7V to 1.9V. Forcing this pin below 0.28V 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 exter-
nal resistive divider across the output.
SENSE (Pin 4): This pin performs two functions. It moni-
tors 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.
BLOCK DIAGRA
5
V_CC
800mV
REFERENCE
V_CC
SHUNT
REGULATOR
0.3μA 0.28V
SHUTDOWN
+
COMPARATOR
–
V_CC < V_{TURNON UNDERVOLTAGE}
LOCKOUT
V_FB
3
GND
2
SOFT-
START
CLAMP
ERROR
+
AMPLIFIER
–
1.2V
I_TH/RUN
1
CURRENT
–
COMPARATOR
R
+
Q
S
20mV
300kHz
OSCILLATOR
SHUTDOWN
SWITCHING
LOGIC AND
BLANKING
CIRCUIT
V_CC
GATE
DRIVER NGATE
6
SLOPE
COMP
CURRENT
RAMP
SENSE
4
38033 BD
38033fa
6