RT9273 데이터 시트보기 (PDF) - Richtek Technology
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RT9273 Datasheet PDF : 14 Pages
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RT9273
Function Block Diagram
Preliminary
VCC
EN
GND
SP
EN
EN
GT
VRF
Dimming Controller
5u
VCC
OVP
EN
ON
VRF
FB
GND
Boost Controller
GT
1ms
Buffer
OVP
LX
CH1
CH2
FB1
FB2
Operation
RT9273 operates at a wide input voltage range suitable for Li-On battery and has a constant high frequency for smaller
inductor and capacitors. The block diagram refers the operation circuit. The scheme is divided into three parts: dimming
controller, boost controller and the logic selection function. By SP pin, it can choose the different channel to turn on CH1
or CH2. As the input signal change, internal MOSFET of LX pin will turn off 1ms to prevent the over voltage damage by
the output voltage instant change.
z The Dimming Controller:
RT9273 uses the PWM signal on EN pin to achieve dimming control. If the period of EN is less than 3ms in 50% duty,
EN is always pulled high. Then EN signal is sent to the next boost controller to enable the function. This action is to
differentiate between shut down and dimming control. VRF offers the reference voltage to error amplifier of next function.
The internal soft start is designed for enable control and dimming control to avoid the inrush current.
z The Boost Controller:
RT9273 uses current mode control scheme to provide better performance of line and load regulation. The boost controller
includes of error amplifier, summing comparator, logic control and protection function. The difference between the feedback
voltage and the reference voltage is send to the negative input of comparator. The comparator also senses the sensing
current from inductor and slope compensation. To keep the output in regulation, the output of summing comparator is
sent to the logic function, and then to control the duty ratio of the MOSFET switch. If the error amplifier's output
increases, the duty of the switch will be larger to deliver more current to the output.
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DS9273-09 August 2007
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