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参数资料
| 型号： | SC668ULTRT |
| 厂商： | Semtech |
| 文件页数： | 20/46页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR LMU 8CH MLPQUT20 |
| 特色产品： | Semtech sc667 and sc668 |
| 标准包装： | 1 |
| 拓扑： | 线性（LDO），PWM |
| 输出数： | 12 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 背光，LED 闪烁器，照明管理装置（LMU） |
| 频率： | 400kHz |
| 电源电压： | 2.9 V ~ 5.5 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-UFQFN 裸露焊盘 |
| 供应商设备封装： | 20-MLPQ（3x3） |
| 包装： | 标准包装 |
| 工作温度： | -40°C ~ 85°C |
| 其它名称： | SC668ULDKR |
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SC668
Applications Information (continued)
ongoing fade, the bank will turn off immediately. When
the backlight bits are re-enabled and BxFEN = 1, the back-
light currents will begin at 0mA and fade to the value
determined by the backlight current register bits IBx[4:0].
If the backlight enable bits are re-enabled and BxFEN = 0,
the main backlights will proceed immediately to the value
of IBx[4:0]. Note that the words “target value” are not used
to describe the final value after a fade operation. “Target
value” is reserved for describing the backlight settings at
the end of the blink or breathe effect cycles.
Non-Programmable Backlight Steps
In addition to the 32 programmable backlight steps, there
are 75 non-programmable steps which are used only
the duty cycle to a DC current level. A DC current is passed
through the LEDs, providing lower noise compared to the
more conventional pulsed current PWM method.
PWM Sampling
The sampling system that translates the PWM signal to a
DC current requires the PWM pin to have a minimum high
time t HIGH_MIN to set the DC level. High time less than t HIGH_MIN
impacts the accuracy of the target I BL . The minimum duty
cycle needed to support the minimum high time specifi-
cation varies with the applied PWM frequency (see Figure
9). Note that use of a lower PWM frequency, from 200Hz
to 10kHz, will support a lower minimum duty cycle and an
extended backlight dimming range.
during a fade or breathe operation. Table 1 provides the
total number of steps between the starting and ending
value of any fade or breathe operation. The value from
Table 1 is multiplied by the fade rate to determine the
total fade time. The maximum possible fade-in duration,
from 0mA to 25mA, or fade-out duration, from 25mA to
0mA, is equal to 106 x 16ms = 1696ms.
Figures 10 through 14 provide additional information
about the non-programmable steps. Each figure repre-
sents one linear segment of the overall fade range shown
in Figure 15. The overall fade range is a piece-wise linear
5
4
3
2
1
t HIGH_MIN = 1μs
approximation of a logarithmic function which provides
for a very smooth visual fading or breathing effect.
0
0.2
10
20 30
PWM Frequency (kHz)
40
50
The fade rate may be changed dynamically when a fade
operation is active by writing new values to the fade reg-
ister. When a new backlight level is written during an
ongoing fade operation, the fade will be redirected to the
new value from the present state. An ongoing fade opera-
tion may be cancelled by disabling fade, which will result
in the backlight current changing immediately to the final
value. If fade is disabled, the current level will change
immediately to the final value without the fade delay.
PWM Operation on Bank #1
A PWM signal on the PWM pin can be used to adjust the
DC current through the LEDs in bank #1. When the duty
cycle is 100%, the backlight current through each LED (I BL )
equals the full scale current value set for bank #1. The
PWM input samples voltage at the PWM pin and converts
Figure 9 — Minimum Duty Cycle
Ambient Light Sense
The SC668 includes a general purpose sigma-delta ADC
that is designed to interface with an ambient light sensor.
The ADC input accepts the output of an external ambient
light sensor circuit. When the ADC is enabled via the I 2 C
bus, the analog signal produced by the ambient light
sensor is compared with two user programmable thresh-
old levels. The result of the comparison is then used to
automatically change the brightness of the LEDs in bank
#1 to a user defined value. This function is used to com-
pensate for ambient lighting conditions — increasing
brightness where brighter ambient conditions exist and
decreasing brightness in lower lighting conditions.
20
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