LTC3803ES6-3#TRMPBF Linear Technology, LTC3803ES6-3#TRMPBF Datasheet - Page 8

• Manufacturer Part Number: LTC3803ES6-3#TRMPBF
• Description: IC FLYBACK SYNC ADJ 1A TSOT23-6
• Manufacturer: Linear Technology
• Type: Flybackr

Specifications of LTC3803ES6-3#TRMPBF

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: Adjustable
• Current - Output: 1A
• Frequency - Switching: 300kHz
• Voltage - Input: Adjustable
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: TSOT-23-6, TSOT-6
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

LTC3803-3
OPERATION
The undervoltage lockout (UVLO) mechanism prevents
the LTC3803-3 from trying to drive a MOSFET with in-
suffi cient V
V
LTC3803-3 operation. The V
to fall to V
lockout disables the LTC3803-3. This wide UVLO hysteresis
range supports the use of a bias winding on the fl yback
transformer to power the LTC3803-3—see the section
Powering the LTC3803-3.
The I
threshold (V
down. An internal 0.3μA current source always tries to
pull this pin towards V
is allowed to exceed V
the LTC3803-3 begins to operate and an internal clamp
immediately pulls the I
operation, the I
0.7V to 1.9V to represent current comparator thresholds
from zero to maximum.
Internal Soft-Start
An internal soft-start feature is enabled whenever the
LTC3803-3 comes out of shutdown. Specifi cally, the I
RUN voltage is clamped and is prevented from reaching
maximum until roughly 1.4ms has passed. This allows
the input and output currents of LTC3803-3-based power
supplies to rise in a smooth and controlled manner on
start-up.
Powering the LTC3803-3
In the simplest case, the LTC3803-3 can be powered from
a high voltage supply through a resistor. A built-in shunt
8
TURNON
TH
/RUN pin can be driven below the shutdown
(nominally 8.7V) at least momentarily to enable
TURNOFF
GS
ITHSHDN
. The voltage at the V
TH
/RUN pin voltage will vary from roughly
(nominally 5.7V) before undervoltage
) to force the LTC3803-3 into shut-
ITHSHDN
CC
TH
. When the I
/RUN pin up to about 0.7V. In
CC
, and V
voltage is then allowed
CC
CC
TH
exceeds V
/RUN pin voltage
pin must exceed
TURNON
TH
/
,
regulator from the V
current as needed through this resistor to regulate the
V
forced to sink more than 25mA. This shunt regulator is
always active, even when the LTC3803-3 is in shutdown,
since it serves the vital function of protecting the V
from seeing too much voltage.
For higher effi ciency or for wide V
fl yback controllers are typically powered through a separate
bias winding on the fl yback transformer. The LTC3803-3
has the wide UVLO hysteresis (1V min) and small V
supply current draw (<90μA when V
needed to support such bootstrapped hysteretic start-up
schemes.
The V
adjacent to the IC pins with a minimum of a 1μF ceramic
or tantalum capacitor. Proper supply bypassing is neces-
sary to supply the high transient currents required by the
MOSFET gate driver.
Adjustable Slope Compensation
The LTC3803-3 injects a 5μA peak current ramp out through
its SENSE pin which can be used for slope compensation in
designs that require it. This current ramp is approximately
linear and begins at zero current at 8% duty cycle, reach-
ing peak current at 80% duty cycle. Additional details are
provided in the Applications Information section.
CC
voltage to around 9.5V as long as the V
CC
pin must be bypassed to ground immediately
CC
pin to GND will draw as much
IN
CC
range applications,
< V
TURNON
CC
pin is not
) that is
CC
38033fd
pin
CC