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Six-String WLED Driver with Integrated
Step-Up Converter
Detailed Description
The MAX17127 is a high-efficiency driver for arrays of
white LEDs. It contains a fixed-frequency current-mode
PWM step-up controller, a 5V linear regulator, a dimming
control circuit, an internal power MOSFET, and six regu-
lated current sources. Figure 2 shows the MAX17127
functional diagram. When enabled, the step-up control-
ler boosts the output voltage to provide sufficient head-
room for the current sources to regulate their respective
string currents. The MAX17127 features resistor-adjust-
able switching frequency (250kHz to 1MHz), which
allows trade-offs between external component size and
operating efficiency.
The MAX17127 can implement brightness control
through the PWM signal input. The LED current is direct-
ly controlled by the external dimming signal's frequency
and duty cycle.
The MAX17127 has multiple features to protect the con-
troller from fault conditions. Separate feedback loops limit
the output voltage in all circumstances. The MAX17127
checks each FB_ voltage during operation.
If one or more strings are open, the corresponding FB_
voltages are pulled below 180mV (max), and an open-
circuit fault is detected. As a result, the respective cur-
rent sources are disabled.
When one or more LEDs are shorted and the related
FB_ voltage exceeds 8V, short fault is detected and the
respective current source is disabled if at least one FB_
voltage is lower than the minimum FB_ regulation voltage
+460mV (typ).
When in LED open or short conditions, the fault string is
disabled while other strings can still operate normally.
The MAX17127 also includes other kinds of fault pro-
tections, which are overcurrent, thermal shutdown, and
output overvoltage. The MAX17127 features cycle-by-
cycle current limit to provide consistent operation and
soft-start protection. In an overcurrent condition, the
IC latches off if the fault still exists after a 128 F s over-
current fault timer expires. The output overvoltage is a
nonlatched operation, and the step-up converter stops
switching during the fault. A thermal-shutdown circuit
provides another level of protection. The MAX17127 is
latched off once thermal shutdown occurs.
The MAX17127 includes a 5V linear regulator that pro-
vides the internal bias and gate driver for the step-up
controller.
Fixed-Frequency Step-Up Controller
The MAX17127’s fixed-frequency, current-mode, step-
up controller automatically chooses the lowest active FB_
voltage to regulate the feedback voltage. Specifically,
the difference between the lowest FB_ voltage and the
current source control signal plus an offset is integrated
at the COMP output. The resulting error signal is com-
pared to the internal switch current plus slope com-
pensation to determine the switch on-time. As the load
changes, the error amplifier sources or sinks current to
the COMP output to deliver the required peak inductor
current. The slope-compensation signal is added to the
current-sense signal in order to improve stability at high
duty cycles.
Internal 5V Linear Regulator and UVLO
The MAX17127 includes an internal low-dropout linear
regulator (V DDIO ). When V IN is higher than 5.0V, this lin-
ear regulator generates a 5V supply to power the internal
PWM controller, control logic, and MOSFET driver. The
V DDIO voltage drops to 3.3V in shutdown. If 5V < V IN <
5.5V, V DDIO and V IN can be connected together and
powered from an external 5V supply. There is a body
diode from V DDIO to V IN , so V IN must be greater than
V DDIO (see Figure 2).
The MAX17127 is disabled until V DDIO exceeds the UVLO
threshold. The hysteresis on UVLO is approximately
250mV. In standby mode, the internal LDO is in low-power
mode with 10 F A (max) input current and approximately
regulated at 3.3V (typ). When EN = high, the internal LDO
is enabled and regulated accurately at 5V (typ).
The V DDIO pin should be bypassed to AGND with a
minimum 1 F F ceramic capacitor.
Startup
At startup, the MAX17127 performs a diagnostic test of
the LED array. In the test phase, all FB_ pins are pulled
up by a given current source (0.4mA min) during 1ms
(typ). If some FB_ voltage is lower than 1.2V (max), the
string is considered to be unused. Therefore, when a
string is not in use, it should be connected to AGND. All
other strings with FB_ higher than 1.2V (max) are detect-
ed as in use. After the LED string diagnostic phases are
finished, the boost converter starts. An additional 1ms
after boost soft-start end is used as minimum FB_ con-
trol. The total startup time is less than 10ms, including
2ms (typ) soft-start. Figure 3 shows the sequence.
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相关代理商/技术参数
MAX17127ETP+T
功能描述:LED照明驱动器 Six String WLED Drvr w/Integrated MOSFET 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
MAX17127EVKIT+
功能描述:电源管理IC开发工具 MAX17127 Eval Kit RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V
MAX17129AETE+
功能描述:LED照明驱动器 Six String WLED Drvr w/Integrated MOSFET 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
MAX17129AETE+T
功能描述:LED照明驱动器 Six String WLED Drvr w/Integrated MOSFET 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
MAX17129ETE+
功能描述:LED照明驱动器 Six String WLED Drvr w/Integrated MOSFET
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
MAX17129ETE+T
功能描述:LED照明驱动器 Six String WLED Drvr w/Integrated MOSFET
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
MAX17129EVKIT+
功能描述:电源管理IC开发工具 MAX17129 Eval Kit
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