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Ultra-High-Efficiency White
LED Drivers
Standard Application Circuits
The standard application circuit of the MAX1984 drives
eight white LEDs (Figure 1). The standard application cir-
cuit of the MAX1985 drives six white LEDs (Figure 6). The
standard application circuit of the MAX1986 drives four
white LEDs (Figure 7). The input voltage range is from
2.7V to 5.5V. Table 1 lists the recommended component
options and Table 2 lists the component suppliers.
Detailed Description
The MAX1984/MAX1985/MAX1986 are white LED dri-
vers that use individual regulators to control the current
of up to eight LEDs. A high-efficiency step-up regulator
generates just enough voltage to keep all the current
regulators in regulation. A versatile dimming interface
accommodates analog, DPWM, or parallel control.
LED Current Regulators
Good LED current matching is achieved using individ-
ual current regulators for each LED (Figure 3). The reg-
ulator is an analog gain block with an open-drain
N-channel MOSFET output stage and can sink up to
Table 1. Component List
25mA LED current. The LED current is sensed using an
internal 1 ? resistor connected between the source of
the MOSFET and ground. The regulator controls the
output current by comparing the voltage across the
current-sense resistor with a reference voltage (IREF)
set by the dimming control circuitry.
Startup and Feedback
The step-up converter is regulated at a voltage just
high enough to power the LEDs. Since the forward volt-
age is different for each LED, the LED with the largest
forward voltage sets the regulation voltage. Each cur-
rent regulator ’ s voltage drop (from LD_ to LDG) is moni-
tored and the lowest voltage drop is used as the
step-up regulator ’ s feedback.
At startup, it is important to ensure the output voltage
rises high enough to forward bias all LEDs and allow their
current regulators to detect their presence. Therefore,
before the current regulators are enabled the step-up
regulator output is made to rise up to the OUT OVP
threshold (5.3V, typ). Then, the step-up regulator stops
switching and each current regulator output is tested
DESIGNATION
C1, C4
D1 – D4, D5*, D6*,
D7**, D8**
L1
MAX1984
2 x 2.2μF, 6.3V X5R ceramic
capacitors (0603)
Taiyo Yuden JMK107BJ225MA
TDK C1608X5ROJ225K
Surface-mount white LEDs
Nichia NSCW215T
10μH, 1A inductor
Sumida CLS5D11HP-100NC
DESCRIPTION
MAX1985
2 x 2.2μF, 6.3V X5R ceramic
capacitors (0603)
Taiyo Yuden JMK107BJ225MA
TDK C1608X5ROJ225K
15μH, 0.85A inductor
Sumida CLS5D11HP-150NC
MAX1986
2.2μF, 6.3V X5R ceramic
capacitors (0603)
Taiyo Yuden JMK107BJ225MA
TDK C1608X5ROJ225K
22μH, 0.65A inductor
Sumida CLS5D11HP-220NC
* MAX1984 and MAX1985 only.
** MAX1984 only.
Table 2. Component Suppliers
SUPPLIER
Nichia
Sumida
Taiyo Yuden
TDK
PHONE
717-285-2323
847-545-6700
800-348-2496
847-803-6100
FAX
717-285-9378
847-545-6720
847-925-0899
847-390-4405
WEBSITE
www.nichia.com
www.sumida.com
www.t-yuden.com
www.component.tdk.com
______________________________________________________________________________________
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相关代理商/技术参数
MAX1986ETE-T 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
MAX1987ETM 制造商:Maxim Integrated Products 功能描述:DUAL-PHASE CONTROLLER FOR IMVP-IV CPU - Rail/Tube
MAX1987ETM+ 制造商:Maxim Integrated Products 功能描述:DUAL-PHASE CONTROLLER FOR IMVP-IV CPU - Rail/Tube
MAX1987ETM+T 制造商:Maxim Integrated Products 功能描述:DUAL-PHASE CONTROLLER FOR IMVP-IV CPU - Tape and Reel 制造商:Maxim Integrated Products 功能描述:DUAL-PHASE QUICK-PWM CTRL TQFN48 PQM
MAX1987ETM-T 制造商:Maxim Integrated Products 功能描述:DUAL-PHASE CONTROLLER FOR IMVP-IV CPU - Tape and Reel
MAX1987EVKIT 制造商:Maxim Integrated Products 功能描述:DUAL-PHASE CONTROLLER FOR IMVP-IV C - Rail/Tube
MAX1988ETM 制造商:Maxim Integrated Products 功能描述:DUAL-PHASE CONTROLLER FOR IMVP-IV CPU - Rail/Tube
MAX1988ETM+ 制造商:Maxim Integrated Products 功能描述:DUAL-PHASE CONTROLLER FOR IMVP-IV CPU - Rail/Tube