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| 型号： | MAX8879ETG+T |
| 厂商： | Maxim Integrated |
| 文件页数： | 13/16页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR WT/RGB BCKLGT 24TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 恒定电流： | 是 |
| 拓扑： | 切换式电容器（充电泵） |
| 输出数： | 11 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 背光 |
| 类型 - 次要： | RGB，白色 LED |
| 频率： | 1MHz |
| 电源电压： | 2.7 V ~ 5.5 V |
| 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-TQFN-EP（4x4） |
| 包装： | 带卷 (TR) |
| 工作温度： | -40°C ~ 85°C |
Charge Pump for Backlight/Flash/RGB LEDs
with Safety Timer
by reducing the LED current above +40°C by approxi-
mately 1.7%/°C. The typical derating function character-
istic is shown in the Typical Operating Characteristics.
The temperature derating function is enabled/disabled
using the I 2 C interface and is off by default.
I 2 C Interface
An I 2 C 2-wire serial interface is provided on the
MAX8879 to control LED brightness, flash, temperature
deration, and RGB ramp rate. The serial interface con-
sists of a serial data line (SDA) and a serial clock line
(SCK). Standard I 2 C write-byte commands are used.
Figure 2 shows a timing diagram for the I 2 C protocol.
The MAX8879 is a slave-only device, relying upon a
master to generate a clock signal. The master (typically
a microprocessor) initiates data transfer on the bus and
generates SCK to permit data transfer. A master device
communicates to the MAX8879 by transmitting the
proper 8-bit address (0x9A) followed by the 8-bit con-
trol byte. Each 8-bit control byte consists of a 3-bit
command code and 5 bits of data (see Table 1). Each
transmit sequence is framed by a START (A) condition
and a STOP (L) condition (see Figure 2). Each word
transmitted over the bus is 8 bits long and is always fol-
lowed by an acknowledge clock pulse.
Shutdown Mode
When all the LEDs are off, the MAX8879 turns off the
charge pump and enters low-power shutdown mode.
When in shutdown, OUT is pulled to GND by an internal
5k Ω resistor, discharging the output capacitor. IN and
PIN are high impedance during shutdown, but the I 2 C
interface (powered from V DD ) remains active. To enter
shutdown, send control byte 0x00 to the I 2 C interface,
and drive FSH high. To exit shutdown, enable any of
the LEDs with the I 2 C interface.
FSH Logic Input
The FSH input is used to control the flash LEDs with the
embedded safety timer. When FSH is driven low, the
flash LEDs are driven to the current set in the Flash reg-
ister. Driving FSH low activates the flash safety timer
with the pre-set time (programmed period). The safety
timer is not activated until an active-low signal is
applied to FSH . This function also serves as a protec-
tion feature to avoid thermal damage to the flash LEDs
because of software-related errors. This pin is the flash-
dedicated control pin.
Movie-Mode Operation
The movie current level is set through the I 2 C interface
according to the current scale in Movie register. The
ON/OFF of movie LEDs is only through I 2 C interface.
Output Overvoltage Protection
In case an LED fails or the cathode is shorted to GND,
the output overvoltage protection limits the output to
5V. When the MAX8879 detects the output voltage ris-
ing above 5V, it shuts off the charge pump. The charge
pump restarts once the output voltage has dropped to
4.9V.
To avoid constantly operating in overvoltage protection,
any unused LED cathode connection (M_, S_, or F_)
must be connected to OUT; this disables the corre-
sponding current regulator.
Thermal Shutdown
Thermal shutdown limits total power dissipation in the
MAX8879. When the junction temperature exceeds
+160°C, the MAX8879 turns off, allowing the IC to cool.
The MAX8879 turns on and begins soft-start after the junc-
tion temperature cools by 20°C. This results in a pulsed
output during continuous thermal-overload conditions.
Applications Information
Input Ripple
In 1x mode, the input ripple of the MAX8879 is negligi-
ble. When the charge pump is switching in 1.5x or 2x
mode, the input ripple depends on the load current and
the output impedance of the source supply. The worst-
case ripple occurs when the charge pump is operating
in 1.5x mode. The switching waveforms in the Typical
Operating Characteristics show the typical input ripple.
For noise-sensitive applications, input ripple can be
reduced by increasing the input capacitance.
Capacitor Selection
Ceramic capacitors are recommended due to their small
size, low cost, and low ESR. Select ceramic capacitors
that maintain their capacitance over temperature and DC
bias. Capacitors with X5R or X7R temperature character-
istics generally perform well. Recommended values are
shown in the Typical Operating Circuit. Using a larger-
value input capacitor helps to reduce input ripple (see
the Input Ripple section).
PCB Layout and Routing
The MAX8879 is a high-frequency switched-capacitor
regulator. For best circuit performance, use a solid
ground plane and place the capacitors as close to the
IC as possible. Connect the exposed pad to GND and
PGND, and allow sufficient copper area for cooling the
IC. Refer to the MAX8879 evaluation kit for an example
PCB layout.
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相关代理商/技术参数 |
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| MAX887EVKIT | 功能描述:直流/直流开关转换器 Evaluation Kit for the MAX887 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX887HESA | 功能描述:直流/直流开关转换器 100% Duty Step-Down DC/DC Converter RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX887HESA+ | 功能描述:直流/直流开关转换器 100% Duty Step-Down DC/DC Converter RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX887HESA+T | 功能描述:直流/直流开关转换器 100% Duty Step-Down DC/DC Converter RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX887HESA-T | 功能描述:直流/直流开关转换器 100% Duty Step-Down DC/DC Converter RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
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