RT9273 데이터 시트보기 (PDF) - Richtek Technology
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RT9273 Datasheet PDF : 14 Pages
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RT9273
Preliminary
Logic control and application circuit for LED and OLED 2 level dimming control
Besides using a PWM signal on EN pin, using logic control can also achieve LEDs and OLED 2 modes dimming control
function. The following application circuit (Figure 7) provides another solution by simple logic control (Table 3).
Formula:
ILED (MIN)
=
VFB1
R4
=
0.3V (typ.)
R4
ILED (MAX)
=
VFB1
R4//R5
=
0.3V (typ.)
R4//R5
VOLED
=
R1+ (R2//R3)
(R2//R3)
× (VFB
-
R1//R2
R3 + (R1//R2)
Vd)
VFB = 0.3 (typ.),
If Vd_low = 0V, Vd_high = 2.8V, VOLED_high = 16.3V, VOLED_low = 13V.
Firstly to set R1=100kΩ, and then get
R2 = 1.92kΩ, R3 = 84.85kΩ
Note: The recommended R1 value is 100kΩ. Choosing R1's value ≤ 100kΩ is proper to the application circuit.
CIN
VIN
2.2uF
Chip Shutdown
Chip Enable
L1
4.7uH SS0520
COUT
2.2uF
VOUT
16.3V
13V
VCC LX
OVP
CH1
EN
RT9273
CH2
SP
FB2
FB1
GND
R5
R4 18
150
Dimm
2.8V
0V
R1
100k
R3
R2
84.85k 1.92k
Figure 7. Application circuit for LED and OLED 2 level dimming control respective
Main ONLY NORMAL
Main ONLY DIMMING
Sub ONLY NORMAL
Sub ONLY DIMMING
SHUT DOWN
Table 3. Truth table for Figure 7
DIMM
EN
SP
H_2.8V/ L_0V
H
L
H
H
L
L
H
H
L
H
H
H
L
Don’t care
Don’t care
Function
ILED = 18mA
ILED = 2mA
VOUT = 16.3V, ILED = 0mA
VOUT = 13V, ILED = 0mA
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DS9273-09 August 2007
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