RT9273 데이터 시트보기 (PDF) - Richtek Technology
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RT9273 Datasheet PDF : 14 Pages
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RT9273
Preliminary
Channel Selection
There is one set of LC filter for RT9273 to share two channels power requirement. Each time turning on only one channel
can save the power dissipation and easily extend the standby time. Selection pin is internal logic controller. SP pin is
pulled low to turn on the internal channel 1 (for LED) and pulling high to turn on channel 2 (for OLED). 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.
Logic control and application circuit for LEDs and OLED turning on simultaneously + 2 modes dimming control
To achieve LEDs and OLED turning on simultaneously, the following application circuit (Figure 5) provides the complete
solution by simple logic control (Table 1).
Formula:
VOUTH
=
R2 + (R8//R7)
(R8//R7)
×
VFB2
;
VOUTL
=
R2 + R7
R7
× VFB2
ILEDH
=
VFB1
(R5//R6)
;
ILEDL
=
VFB1
R5
R3
=
VOUT
− 3VF(LED)
ILED
CIN
VIN
2.2uF
R1
4.7k
WLED_ON
EL_ON
L1
4.7uH SS0520
COUT
2.2uF
VCC LX
OVP
CH1
EN
RT9273
SP
CH2
FB2
GND FB1
R2
1M
R3
300
WLED_ON
R6
R5 20
82
R8
R7 100k
24k
Dimm
Figure 5. Application circuit for LED and OLED turning on simultaneously
Table 1. Truth table for Figure 5
WLED_ON EL_ON DIMM
M & S turn on simultaneously Normal
H
H
H
M & S turn on simultaneously Dimming
--
Main ONLY Normal
H
Main ONLY Dimming
H
Sub ONLY Normal
L
Sub ONLY Dimming
L
SHUT DOWN
L
--
--
L
H
L
L
H
H
H
L
L
Don’t care
Function
VOUT = 16V,
ILED = [VOUT - 3VF(LED)]/R3 mA
--
VOUT = 9.5V, ILED = 18.5 mA
VOUT = 9.5V, ILED = 3.6 mA
VOUT = 13V, ILED = 0 mA
VOUT = 16V, ILED = 0 mA
VOUT = 0V, ILED = 0 mA
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10
DS9273-09 August 2007
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