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参数资料
| 型号： | MAX8790ETP+ |
| 厂商： | Maxim Integrated |
| 文件页数： | 13/24页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR WHITE BCKLGT 20-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 75 |
| 拓扑： | PWM，升压（升压） |
| 输出数： | 6 |
| 内部驱动器： | 无 |
| 类型 - 主要： | 背光 |
| 类型 - 次要： | 白色 LED |
| 频率： | 1MHz |
| 电源电压： | 4.5 V ~ 5.5 V，5.5 V ~ 26 V |
| 输出电压： | 5V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-WFQFN 裸露焊盘 |
| 供应商设备封装： | 20-TQFN-EP |
| 包装： | 管件 |
| 工作温度： | -40°C ~ 85°C |
| 产品目录页面： | 1424 (CN2011-ZH PDF) |
Six-String White LED Driver with Active
Current Balancing for LCD Panel Applications
Startup
At startup, the MAX8790 checks each FB_ pin to deter-
mine if the respective current string is enabled. Each
FB_ pin is internally pulled up with a 10μA current
source. If an FB_ pin is connected to GND, the corre-
sponding string current source is disabled. This feed-
back scan takes approximately 264μs, after which the
step-up converter begins switching.
Shutdown
When the SHDN pin is less than 0.8V, the MAX8790
shuts down the internal LDO, the reference, current
sources, and all control circuitry. The resulting supply
current is less than 10μA. While the n-channel MOSFET
is turned off, the step-up regulator’s output is connected
to IN through the external inductor and rectifier diode.
Frequency Selection
A tri-level OSC input sets the internal oscillator frequency
for the step-up converter, as shown in Table 1. High-fre-
quency (1MHz) operation optimizes the regulator for the
smallest component size, at the expense of efficiency
due to increased switching losses. Low-frequency
(500kHz) operation offers the best overall efficiency, but
requires larger components and PCB area.
Table 1. Frequency Selection
off within 10μs, enabling PWM frequencies of up to
2kHz. All LED full-scale currents are identical and are
set through the ISET pin (15mA < I LED < 25mA).
The minimum voltage drop across each current source
is approximately 450mV at 20mA. The low voltage drop
helps reduce dissipation while maintaining sufficient
compliance to control the LED current within the
required tolerances.
The LED current sources can be disabled by grounding
the respective FB_ pin at startup. When the IC is pow-
ered up, the controller scans settings for all FB_ pins. If
an FB_ pin is not grounded, an internal circuit pulls this
pin high, and the controller enables the corresponding
current source to regulate the string current. If the FB_ pin
is grounded, the controller disables the corresponding
current regulator. The current regulator cannot be dis-
abled by grounding any of the FB_ pins after the IC is
powered up.
All FB_ pins in use are measured and the highest signal
(HVC) and the lowest signal (LVC) are extracted for two
feedback loops. HVC is used to identify excessive dis-
sipation across the current-source inputs. When HVC is
greater than V CC + 0.6V (typ) for greater than 65ms
(see the Current-Source Fault Protection section), a
fault latch is set and the MAX8790 is shut down. The
OSC
GND
Open
V CC
SWITCHING FREQUENCY (kHz)
500
750
1000
LDO output is not affected by the fault latch. LVC is fed
into the step-up converter’s error amplifier to regulate
the step-up converter’s output voltage.
Current-Source Fault Protection
The LED current sources are protected against string
Overvoltage Protection
To protect the step-up converter when the load is open,
or the output voltage becomes excessive for any rea-
son, the MAX8790 features a dedicated overvoltage
feedback input (OV). The OV pin is connected to the
center tap of a resistive voltage-divider from the high-
voltage output (see Figure 1). When the MAX8790 is
powered up, if none of the LED strings on FB1–FB6 are
connected to the step-up converter output, the step-up
converter regulates the output voltage to V OUT =
1.23V(1 + R1 / R2). When V OV exceeds 1.23V, a com-
parator turns off N1. The step-up converter switch is
reenabled after the output voltage drops below the pro-
tection threshold.
LED Current Sources
Maintaining uniform LED brightness and dimming
capability are critical for LCD backlight applications.
The MAX8790 is equipped with a bank of six matched
current sources. These specialized current sources are
accurate to within ±1.5% and can be switched on and
open, short, and gross mismatch faults, using overvolt-
age detection circuitry on each FB_ pin. If any of these
three fault conditions persists for a preset duration, the
MAX8790 is latched off. The duration of the fault time
depends on the dimming mode and the duty cycle of
the BRT input (D BRT ). In the DPWM mode, the timeout
interval is:
t TIMEOUT_DPWM = 65ms/D BRT
In analog dimming mode, the fault time is fixed at 65ms
for D BRT greater than 12.5%. When D BRT is less than
12.5%, the timeout interval is:
t TIMEOUT_ANALOG = 8.125ms/D BRT
The fault latch can be cleared by cycling the power or
toggling the shutdown pin SHDN .
Open-Current Source Protection
The MAX8790 step-up converter output voltage is regu-
lated according to the minimum value of the enable FB_
voltages. If an individual LED string is open, the respec-
tive FB_ is pulled down to near ground. In this situation,
the step-up converter output voltage increases but is
______________________________________________________________________________________
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8790ETP+ | 功能描述:LED照明驱动器 Six-String White LED Driver 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 |
| MAX8790ETP+T | 功能描述:LED照明驱动器 Six-String White LED Driver 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 |
| MAX8790EVKIT+ | 功能描述:LED 照明开发工具 RoHS:否 制造商:Fairchild Semiconductor 产品:Evaluation Kits 用于:FL7732 核心: 电源电压:120V 系列: 封装: |
| MAX8791AGTA+ | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX8791AGTA+T | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
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