ltc3803es6-5 Linear Technology Corporation, ltc3803es6-5 Datasheet - Page 8

• Manufacturer Part Number: ltc3803es6-5
• Description: Constant Frequency Current Mode Flyback Dc/dc Controller In Thinsot
• Manufacturer: Linear Technology Corporation

OPERATIO
LTC3803-5
The I
control loop. Typically, an external series RC network is
connected from I
optimal response to load and line transients. The imped-
ance of this RC network converts the output current of the
error amplifier to the I
current comparator threshold and commands consider-
able influence over the dynamics of the voltage regulation
loop.
Start-Up/Shutdown
The LTC3803-5 has two shutdown mechanisms to disable
and enable operation: an undervoltage lockout on the V
supply pin voltage, and a forced shutdown whenever
external circuitry drives the I
5 transitions into and out of shutdown according to the
state diagram (Figure 1).
8
(NOMINALLY 4V)
V
CC
TH
< V
TURNOFF
/RUN pin serves as the compensation point for the
Figure 1. Start-Up/Shutdown State Diagram
U
TH
/RUN to ground and is chosen for
SHUT DOWN
LTC3803-5
LTC3803-5
TH
ENABLED
/RUN voltage which sets the
TH
V
(NOMINALLY 0.28V)
ITH/RUN
/RUN pin low. The LTC3803-
38035 F01
< V
ITHSHDN
V
AND V
(NOMINALLY 4.8V)
ITH/RUN
CC
> V
> V
ITHSHDN
TURNON
CC
The undervoltage lockout (UVLO) mechanism prevents
the LTC3803-5 from trying to drive a MOSFET with insuf-
ficient V
V
LTC3803-5 operation. The V
fall to V
out disables the LTC3803-5.
The I
0.28V) to force the LTC3803-5 into shutdown. An internal
0.3μA current source always tries to pull this pin towards
V
V
to operate and an internal clamp immediately pulls the
I
pin voltage will vary from roughly 0.7V to 1.9V to repre-
sent current comparator thresholds from zero to maxi-
mum.
Internal Soft-Start
An internal soft-start feature is enabled whenever the
LTC3803-5 comes out of shutdown. Specifically, the
I
ing maximum until roughly 0.7ms has passed. This
allows the input and output currents of LTC3803-5-
based power supplies to rise in a smooth and controlled
manner on start-up.
TH
TH
TURNON
CC
SHDN
/RUN pin up to about 0.7V. In operation, the I
/RUN voltage is clamped and is prevented from reach-
. When the I
TH
, and V
TURNOFF
/RUN pin can be driven below V
GS
(nominally 4.8V) at least momentarily to enable
. The voltage at the V
CC
(nominally 4V) before undervoltage lock-
exceeds V
TH
/RUN pin voltage is allowed to exceed
TURNON
CC
voltage is then allowed to
, the LTC3803-5 begins
CC
pin must exceed
SHDN
(nominally
TH
/RUN
38035fb