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High-Power Synchronous HBLED
Drivers with Rapid Current Pulsing
Voltage-Error Amplifier (VEA)
The VEA sets the gain of the voltage control loop, and
determines the error between the differential amplifier
output and the internal reference voltage. The VEA out-
put clamps to 0.93V relative to the internal common-
mode voltage, V CM (+0.6V), limiting the average maxi-
mum current. The maximum average current-limit
threshold is equal to the maximum clamp voltage of the
VEA divided by the gain (34.5) of the current-sense
amplifier. This results in accurate settings for the aver-
age maximum current.
MOSFET Gate Drivers
The high-side (DH) and low-side (DL) drivers drive the
gates of external n-channel MOSFETs. The drivers’ 4A
peak sink- and source-current capability provides
ample drive for the fast rise and fall times of the switch-
ing MOSFETs. Faster rise and fall times result in
reduced cross-conduction losses. Size the high-side
and low-side MOSFETs to handle the peak and RMS
currents during overload conditions. The driver block
also includes a logic circuit that provides an adaptive
nonoverlap time to prevent shoot-through currents dur-
ing transition. The typical nonoverlap time is 35ns
between the high-side and low-side MOSFETs.
BST
The MAX16821A/MAX16821B/MAX16821C provide
Current Limit
The error amplifier (VEA) output is clamped between
-0.050V and +0.93V with respect to common-mode
voltage (V CM ). Average current-mode control limits the
average current sourced by the converter during a fault
condition. When a fault condition occurs, the VEA out-
put clamps to +0.93V with respect to the common-
mode voltage (0.6V) to limit the maximum current
sourced by the converter to I LIMIT = 0.0275 / R S .
Overvoltage Protection
The OVP comparator compares the OVI input to the
overvoltage threshold. The overvoltage threshold is typ-
ically 1.127 times the internal 0.6V reference voltage
plus V CM (0.6V). A detected overvoltage event trips the
comparator output turning off both high-side and low-
side MOSFETs. Add an RC delay to reduce the sensi-
tivity of the overvoltage circuit and avoid unnecessary
tripping of the converter (Figure 4). After the OVI volt-
age falls below 1.076V (typ.), high-side and low-side
drivers turn on only after a 2048 clock-cycle POR and a
1024 clock-cycle soft-start have elapsed. Disable the
overvoltage function by connecting OVI to SGND.
C OVI
power to the low-side and high-side MOSFET drivers
through V DD . A bootstrap capacitor from BST to LX pro-
vides the additional boost voltage necessary for the
high-side driver. V DD supplies power internally to the
low-side driver. Connect a 0.47μF low-ESR ceramic
capacitor between BST and LX and a Schottky diode
from BST to V DD .
MAX16821A
MAX16821B
MAX16821C
OVI
DIFF
RB
RA
V OUT
Protection
The MAX16821A/MAX16821B/MAX16821C include out-
put overvoltage protection (OVP). During fault condi-
EAN
R IN
tions when the load goes to high impedance (output
opens), the controller attempts to maintain LED current.
The OVP disables the MAX16821A/MAX16821B/
MAX16821C whenever the output voltage exceeds the
OVP threshold, protecting the external circuits from
EAOUT
R F
undesirable voltages.
Figure 4. Overvoltage Protection Input Delay
12
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相关代理商/技术参数
MAX16821EVKIT+ 制造商:Maxim Integrated Products 功能描述:HIGH-POWER SYNCHRONOUS HBLED DRIVER - Boxed Product (Development Kits)
MAX16822AASA/V+ 功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense 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
MAX16822AASA/V+T 功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense 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
MAX16822AASA+ 功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense 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
MAX16822AASA+T 功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense 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
MAX16822BASA+ 功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense 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
MAX16822BASA+T 功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense 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
MAX16822BEVKIT+ 功能描述:LED 照明开发工具 MAX16822B Eval Kit 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: