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RT8555AWSC

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P26
19
DS8555-01 August 2016 www.richtek.com
RT8555
©
Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
Smart Dither Slope Time Control
The smart dither slope time control could be set by the I
2
C, it is shown in the Table 16.
Table 16. Smart Dither Slop Time Control
Smart dither slope time can be control by address 08h[6:4], there are many difference brightness times that adjust
range from 7.8ms to 500ms. When the smart dither slope command is below B000, the slope time that is the dimming
duty from 0% to 100% will be kept at 7.8ms. This function can guarantee the highest of slope time is 500ms. The
resolution is shown in Table 17.
Address Bit Name Default Value Description Resolution R/W
08h [6:4]
Smart Dither
Slope Time
Control
B000
Slope time control
B000 : 7.8ms
B001 : 7.8ms
B010 : 15.625ms
B011 : 31.25ms
B100 : 62.5ms
B101 : 125ms
B110 : 250ms
B111 : 500ms
-- R/W
09h [4:4]
Smart Dither
Enable
B1
Smart dither enable
B0 : Disable
B1 : Enable
-- R/W
Table 17. Smart Dither Resolution
Time (period T)
10 bit mode
0T~1T 1T~2T 2T~3T 3T~4T 4T~5T 5T~6T 6T~7T
Dimming Duty (%)
0~
1.5625%
1.5625%
~3.125%
3.125%
~6.25%
6.25%
~12.5%
12.5%
~25%
25%
~50%
50%
~100%
Resolution (step) 1024 512 512 512 512 512 511
Slope Time Setting
7.8ms
1.114ms 1.114ms
1.114ms 1.114ms 1.114ms 1.114ms 1.114ms
Figure 10. LED Current (Dimming Up) vs. Time Figure 11. LED Current (Dimming Down) vs. Time
Smart Dither Slope Control (Dimming Down)
0
10
20
30
40
50
60
70
80
90
100
01234567
Time (period T)
LED Current (%)
0% to 100% total 7T
Smart Dither Slope Control (Dimming Up)
0
10
20
30
40
50
60
70
80
90
100
01234567
Time (period T)
LED Current (%)
0% to 100% total 7T
20
DS8555-01 August 2016www.richtek.com
RT8555
©
Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
Dither Resolution Control
The dither resolution control could be set by the I
2
C, it is shown in the Table 18.
Table 18. Dither Slop Time Control
Dither resolution can be control by address 09h[1:0], there are four kind of dither resolution that are from 0 bit to 3 bit.
When the command is below B00, the dither resolution that is the dimming duty from 0% to 100% will be kept at 0 bit.
This function can guarantee the highest of dither resolution is 3 bit. The dither resolution is shown in Table 19.
Address Bit Name Default Value Description Resolution R/W
09h [1:0]
Dither
Resolution
B00
Dither resolution
B00 : 0 bit
B01 : 1 bit
B10 : 2 bit
B11 : 3 bit
-- R/W
09h [2:2]
PWM Dither
Enable
B1
PWM dither enable
B0 : Disable
B1 : Enable
-- R/W
09h [3:3]
DC Dither
Enable
B1
DC dither enable
B0 : Disable
B1 : Enable
-- R/W
Table 19. Dither Resolution
Dimming Duty (%)
Resolution
(
step
)
x Step Time
(
s
)
0~
1.5625%
1.5625%~
3.125%
3.125%
~6.25%
6.25%
~12.5%
12.5%
~25%
25%
~50%
50%
~100%
Total Time (s)
(0%~100%)
No DC dither
09h[3:3] = 0
16 x 1s 16 x 1s 32 x 1s 64 x 1s 128 x 1s
256 x
1s
511 x
1s
1023s
0bit dither 32 x 16s 32 x 16s 64 x 8s
128 x
4s
256 x 2s
512 x
1s
511 x
1s
3583s
1bit dither 64 x 16s 64 x 16s 128 x 8s
256 x
4
s
512 x 1s
512 x
2
s
511 x
2
s
7166s
2bit dither 128 x 16s 128 x 16s 256 x 8s
512 x
4
s
512 x 4s
512 x
4
s
511 x
4
s
14332s
3bit dither 256 x 16s 256 x 16s 512 x 8s
512 x
8
s
512 x 8s
512 x
8
s
511 x
8
s
28664s
Note : Fade Time is 1s (09h[6:5] = B01)
Figuer 12. LED Current (Dimming Up) vs. Time Figuer 13. LED Current (Dimming Down) vs. Time
Dither Resolution (Dimming Down)
0
10
20
30
40
50
60
70
80
90
100
0 4200 8400 12600 16800 21000 25200 29400
Time (µs)
LED Current (%)
No Dither
0Bit
1Bit
2Bit
3Bit
Dither Resolution (Dimming Up)
0
10
20
30
40
50
60
70
80
90
100
0 4200 8400 12600 16800 21000 25200 29400
Time (µs)
LED Current (%)
No Dither
0Bit
1Bit
2Bit
3Bit
21
DS8555-01 August 2016 www.richtek.com
RT8555
©
Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
26KHz Mode Division Frequency
The 26KHz mode division frequency could be set by the I
2
C, it is shown in the Table 20.
Table 20. 26KHz Mode Division Frequency
The 26kHz mode division frequency can be control by address 0Ah[7:5], there are five kind of division frequency that
contain 26KHz, 26KHz/2, 26KHz/4, 26KHz/8 and 26KHz/16. When the command is below B000, the PWMO frequency
that is the 26kHz mode will be kept at 26KHz. This function can guarantee the most of division frequency is division 16
time.
Address Bit Name Default Value Description Resolution R/W
0Ah [7:5]
26KHz mode
division
frequency
B000
PWMO frequency
B000 : 26KHz
B001 : 26KHz/2
B010 : 26KHz/4
B011 : 26KHz/8
B1xx : 26KHz/16
-- R/W
Control CLK PFM Function Enable
The CLK PFM function enable could be set by the I
2
C, it is shown in the Table 21.
Table 21. Control CLK PFM Function Enable
The CLK PFM function enable can be control by address 0Dh[7:7]. If the bit equals to 0, it means the boost switching
frequency just depends on the switching frequency setting. Otherwise, if the bit equals to 1, the boost switching
frequency will be decreased, when the boost on time is lower than the minimum on time.
LED Protection
RT8555 has LED protection for LED OVP level, LED unused. The LED protection could be set by the I
2
C, it is shown in
the Table 22.
Table 22. LED Protection
Address Bit Name Default Value Description Resolution R/W
0Dh [7:7]
Control CLK
PFM function
enable
B0
Control CLK PFM function
enable
B0 : off
B1 : on
-- R/W
Address Bit Name Default Value Description Resolution R/W
0Eh [3:2]
LED OVP
level
B00
LED OVP level
B00 : 2.1V
B01 : 2.52V
B10 : 2.8V
B11 : 3.5V
-- R/W
0Eh [5:5]
LED unused
check
B0
LED unused check
B0 : Disable
B1 : Enable
-- R/W
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RT8555AWSC

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