参数资料
型号: LTC3803IS6#TRMPBF
厂商: Linear Technology
文件页数: 8/16页
文件大小: 0K
描述: IC REG CTRLR FLYBK PWM TSOT23-6
标准包装: 500
PWM 型: 电流模式
输出数: 1
频率 - 最大: 240kHz
占空比: 90%
电源电压: 5.7 V ~ 8 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 125°C
封装/外壳: SOT-23-6 细型,TSOT-23-6
包装: 带卷 (TR)
相关产品: 732-2263-6-ND - TRANS FLYBACK LTC3803 16.9UH
732-2263-1-ND - TRANS FLYBACK LTC3803 16.9UH
732-2263-2-ND - TRANS FLYBACK LTC3803 16.9UH
其它名称: LTC3803IS6#PBF
LTC3803IS6#PBF-ND
LTC3803
OPERATION
The undervoltage lockout (UVLO) mechanism prevents the
LTC3803 from trying to drive a MOSFET with insuf?cient
V GS . The voltage at the V CC pin must exceed V TURNON
(nominally 8.7V) at least momentarily to enable LTC3803
operation. The V CC voltage is then allowed to fall to V TURNOFF
(nominally 5.7V) before undervoltage lockout disables the
LTC3803. This wide UVLO hysteresis range supports the
use of a bias winding on the ?yback transformer to power
the LTC3803—see the section Powering the LTC3803.
The I TH /RUN pin can be driven below V ITHSHDN (nominally
0.28V) to force the LTC3803 into shutdown. An internal
0.3μA current source always tries to pull this pin towards
V CC . When the I TH /RUN pin voltage is allowed to exceed
V ITHSHDN , and V CC exceeds V TURNON , the LTC3803 begins
to operate and an internal clamp immediately pulls the
I TH /RUN pin up to about 0.7V. In operation, the I TH /RUN
pin voltage will vary from roughly 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 comes out of shutdown. Speci?cally, the I TH /
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-based power
supplies to rise in a smooth and controlled manner on
start-up.
Powering the LTC3803
In the simplest case, the LTC3803 can be powered from
a high voltage supply through a resistor. A built-in shunt
regulator from the V CC pin to GND will draw as much
current as needed through this resistor to regulate the
V CC voltage to around 9.5V as long as the V CC pin is not
forced to sink more than 25mA. This shunt regulator is
always active, even when the LTC3803 is in shutdown,
since it serves the vital function of protecting the V CC pin
from seeing too much voltage.
For higher ef?ciency or for wide V IN range applications,
?yback controllers are typically powered through a separate
bias winding on the ?yback transformer. The LTC3803 has
the wide UVLO hysteresis and small V CC supply current
draw that is needed to support such bootstrapped hysteretic
start-up schemes.
The V CC pin must be bypassed to ground immediately
adjacent to the IC pins with a minimum of a 10μF 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 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 6% duty cycle, reach-
ing peak current at 80% duty cycle. Additional details are
provided in the Applications Information section.
3803fc
8
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