- 您现在的位置：买卖IC网 > PDF目录16548 > MAX1578ETG+ (Maxim Integrated Products)IC PS BIAS/WHITE LED TFT 24-TQFN PDF资料下载
参数资料
| 型号： | MAX1578ETG+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 10/13页 |
| 文件大小： | 0K |
| 描述： | IC PS BIAS/WHITE LED TFT 24-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 75 |
| 应用： | LCD 显示器 |
| 电流 - 电源： | 3mA |
| 电源电压： | 2.7 V ~ 5.5 V |
| 工作温度： | -40°C ~ 85°C |
| 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： | 管件 |
Complete Bias and White LED Power Supplies
for Small TFT Displays
Soft-Start
The LED boost converter utilizes a soft-start function to
eliminate inrush current during startup. Once the boost
converter is enabled, LX begins switching at the mini-
mum duty cycle until C COMP is charged to 1.25V. Once
this occurs, the duty cycle increases to further charge
the output until V CS reaches 20% of V CTRL . The soft-
start time is adjustable using the capacitor from COMP
to GND. Calculate the required COMP capacitor as:
Drive ONBIAS low to shut down the internal POS and
NEG charge pumps and disable the MAIN LDO output.
On-chip pulldown resistors discharge these outputs
during shutdown. Drive ONBIAS high for normal opera-
tion. V DD is connected to IN when ONBIAS is low. The
quiescent current is reduced to 430μA when the charge
pumps are shut down and the boost converter is
enabled.
Applications Information
C COMP =
12 μ A × t SS
1 . 25 V
Adjusting LED Current
Set the maximum LED current using a resistor from CS
where t SS is the desired soft-start time in seconds.
to GND. Calculate the resistance as follows:
Overvoltage Protection
The output of the LED boost converter is protected from
overvoltage conditions by internal overvoltage circuitry.
If V OUT exceeds 34V, the LX switching terminates.
Once V OUT falls below 32V, LX switches normally and
R CS =
R CS =
330 mV
I LED
340 mV
I LED
for the MAX 1578
for the MAX 1579
soft-start is re-initiated.
Ambient Temperature Derating Function
(MAX1579)
The MAX1579 limits the maximum LED current depend-
ing on the die temperature. V CS is limited to 340mV up
to +42 ° C. Once the temperature reaches +42 ° C, the
maximum V CS declines by 6mV/ ° C until the minimum
40mV threshold is reached at +100 ° C. Due to the pack-
age’s exposed paddle, the die temperature is always
very close to the PC board temperature.
The temperature derating function allows the LED cur-
rent to be safely set higher at normal operating temper-
atures, thereby allowing either a brighter display or
fewer LEDs to be used for normal display brightness.
Shutdown
The MAX1578/MAX1579 include a low-quiescent-current
shutdown mode. To enter shutdown, drive CTRL below
0.1V for longer than 10.5ms and drive ONBIAS low. The
quiescent current is reduced to less than 1μA when the
boost converter and charge pumps are disabled.
To disable the LED boost converter, drive CTRL below
0.1V for longer than 10.5ms. During shutdown, the
internal boost switch from LX to PGND is high imped-
ance; however, a DC path exists from IN to OUT
through the external inductor and Schottky diode. Drive
CTRL with an analog voltage between 0.24V and 1.65V
or a 200Hz to 200kHz digital PWM dimming signal for
normal operation. The quiescent current is reduced to
870μA when the boost converter is shut down and the
charge pumps are enabled.
where I LED is the desired maximum current through the
LEDs in Amps when V CTRL is 1.65V.
LED Dimming Control Using a DAC
V CTRL controls the LED drive current. The voltage at CS
regulates to 20% of V CTRL to control the current
through the LEDs and, therefore, the brightness. Drive
CTRL using a DAC with an output voltage between
0.24V and 1.65V to control the brightness of the LEDs.
Increasing V CTRL beyond 1.65V results in no further
brightness increase. Hold CTRL below 100mV for
longer than 10.5ms to shut down the boost converter.
LED Dimming Using Direct PWM into CTRL
Another useful technique for LED dimming control is the
application of a logic-level PWM signal applied directly
to CTRL. LED current may be varied from zero to full
scale. The frequency range of the PWM signal is from
200Hz to 200kHz, while 0% duty cycle corresponds to
zero current and 100% duty cycle corresponds to full
current. The error amplifier and compensation capaci-
tor form a lowpass filter so PWM dimming results in DC
current to the LEDs without the need for any additional
RC filters. See the Typical Operating Characteristics .
Input/Output Ripple
For LED drivers, input and output ripple may be impor-
tant. Input ripple depends on the source supply’s output
impedance. Adding a lowpass filter to the input further
reduces input ripple. Alternately, increasing C IN to 10μF
cuts input ripple in half. Likewise, an output filter or high-
er output capacitance value reduces output ripple.
10
______________________________________________________________________________________
相关PDF资料 |
PDF描述 |
|---|---|
| MAX769EEI+T | IC PAGER SYSTEM 28-QSOP |
| GCA22DTKI-S288 | CONN EDGECARD 44POS .125 EXTEND |
| HSC05DRTF-S13 | CONN EDGECARD 10POS .100 EXTEND |
| GSA10DRSI-S288 | CONN EDGECARD 20POS .125 EXTEND |
| GMA10DRSI-S288 | CONN EDGECARD 20POS .125 EXTEND |
相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1578ETG+ | 功能描述:LED照明驱动器 Cmplete Bias & White LED Power Supply RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N |
| MAX1578ETG+T | 功能描述:LED照明驱动器 Cmplete Bias & White LED Power Supply RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N |
| MAX1578ETG-T | 功能描述:LED照明驱动器 Cmplete Bias & White LED Power Supply RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N |
| MAX1579ETG | 功能描述:LED照明驱动器 RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N |
| MAX1579ETG+ | 功能描述:LED照明驱动器 Cmplete Bias & White LED Power Supply RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N |
发布紧急采购，3分钟左右您将得到回复。