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| 型号： | LP5521YQX/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 14/44页 |
| 文件大小： | 0K |
| 描述： | IC LED DRIVER RGB 24-LLP |
| 标准包装： | 4,500 |
| 系列： | PowerWise® |
| 恒定电流： | 是 |
| 拓扑： | PWM，切换式电容器（充电泵） |
| 输出数： | 3 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 背光，照明管理装置（LMU） |
| 类型 - 次要： | RGB |
| 频率： | 1.25MHz |
| 电源电压： | 2.7 V ~ 5.5 V |
| 输出电压： | 4.55V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-WFQFN 裸露焊盘 |
| 供应商设备封装： | 24-LLP |
| 包装： | 带卷 (TR) |
| 工作温度： | -30°C ~ 85°C |
| 其它名称： | LP5521YQX |
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SNVS441F – JANUARY 2007 – REVISED FEBRUAY 2013
LED FORWARD VOLTAGE MONITORING
When charge pump automatic mode selection is enabled, voltages over LED drivers are monitored. If drivers do
not have enough headroom, charge pump gain is set to 1.5x. Driver saturation monitor does not have a fixed
voltage limit, since saturation voltage is a function of temperature and current. Charge pump gain is set to 1x,
when battery voltage is high enough to supply all LEDs.
In automatic gain change mode, charge pump is switched to bypass mode (1x), when LEDs are inactive for over
50 ms.
Charge pump gain control utilizes digital filtering to prevent supply voltage disturbances from triggering gain
changes. If R driver current source is connected to battery (address 08H, bit R_TO_BATT = 1) voltage
monitoring is disabled in R output, but still functional in B and G output.
LED forward voltage monitoring and gain control block diagram is shown below.
Charge
Pump
VOUT
Current
Source
V OFS
PWM
Saturation
MODE
Monitor
R/G/B
Comparator
Digital
Filter
Control
Registers
Program
Memory
Command
Look-ahead
Mode
Control
Figure 24. Voltage monitoring block diagram for one output
LED DRIVER OPERATIONAL DESCRIPTION
The LP5521 LED drivers are constant current sources with 8-bit PWM control. Output current can be
programmed with I 2 C register up to 25.5 mA. Current setting resolution is 100 μ A (8-bit control).
R driver has two modes: current source can be connected to battery (V DD ) or to charge pump output. If current
source is connected to battery, automatic charge pump gain control is not used for this output. This approach
provides better efficiency when LED with low V F is connected to R driver, and battery voltage is high enough to
drive this LED in all conditions. R driver mode can be selected with I 2 C register bit. When address 08H, bit
R_TO_BATT = 1, R current source is connected to battery. When it is 0 (default), R current source is connected
to charge pump same way as in G and B drivers. G and B drivers are always connected to charge pump output.
Some LED configuration examples are given in table below. When LEDs with low V F are used, charge pump can
be operating in bypass mode (1x). This eliminates the need of having double drivers for all outputs; one
connected to battery and another connected to charge pump output. When LP5521 is driving a RGB LED, R
channel can be configured to use battery power. This configuration increases power efficiency by minimizing the
voltage drop across the LED driver.
Table 2. LED configuration examples
Configuration
R output to BATT
R output to CP
CP Mode
RGB LED with low V F red
3 x low V F LED
3 x white LED
1 x low V F LED (R output)
X
X
X
X
Auto (1x or 1.5x)
1x
Auto (1x or 1.5x)
Disabled
PWM frequency is either 256 Hz or 558 Hz, frequency is set with PWM_HF bit in register 08H. When PWM_HF
is 0, then the frequency is 256 Hz, and when bit is 1 then the PWM frequency is 558 Hz. Brightness adjustment
is either linear or logarithmic. This can be set with register 00H LOG_EN bit. When LOG_EN = 0 linear
adjustment scale is used, and when LOG_EN = 1 logarithmic scale is used. By using logarithmic scale the visual
effect seems linear to the eye. Register control bits are presented in following tables:
14
Product Folder Links: LP5521
Copyright ? 2007–2013, Texas Instruments Incorporated
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