LTC3803 Datasheet, PDF (5/12 Pages) Linear Technology – Constant Frequency Current Mode Flyback DC/DC Controller in ThinSOT

LTC3803
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 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
200kHz
OSCILLATOR
SHUTDOWN
SWITCHING
LOGIC AND
BLANKING
CIRCUIT
V_CC
GATE
DRIVER _NGATE
6
SLOPE
COMP
CURRENT
RAMP
SENSE
4
3803 BD
3803i
5