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Ultra-Efficient Negative Charge-Pump LED
Driver with Dual LDOs in 3mm x 3mm Thin QFN
MAX8822
MAX8822
LED
CURRENT
NEG
V IN
LED
CURRENT
NEG
V IN
CONTROL
CONTROL
CURRENT
LED_
I LED_
V LED_ > SWITCHOVER
THRESHOLD
CURRENT
LED_
I LED_
V LED_ < SWITCHOVER
THRESHOLD
REGULATOR
Figure 4. Current Regulator Returning to GND
The LED current and LDO output voltages are pro-
grammed using a serial-pulse control interface. Pulse
ENLED low (as discussed in the LED Dimming Control
section) to decrease the LED current from 24mA to
0.1mA, or hold ENLED low for at least 2.5ms to place the
LED current regulators in shutdown mode. LED dimming
is controlled in 31 pseudo-logarithmic steps. Pulse
ENLDO low (as discussed in the LDO1/LDO2 Output
Voltage Control section) to choose LDO1 and LDO2 out-
put voltages from one of 16 combinations including off.
Drive both ENLED and ENLDO low for at least 2.5ms to
place the IC in low-power (0.5μA typ) shutdown mode.
The MAX8822 includes soft-start, thermal shutdown, and
open- and short-circuit protection.
Adaptive Current Regulator Switchover
When V IN is higher than the forward voltage of an LED
plus the 150mV (typ) dropout voltage of the current
regulator, the LED current returns through GND (Figure
4). If this condition is satisfied for all four WLEDs, the
charge pump remains inactive. When V IN drops such
that the current regulator voltage (V LED_ ) cannot be
maintained above the dropout voltage for any of the
individual LEDs, the charge pump activates and gener-
ates a voltage on NEG that is no greater than 5V (typ)
below V IN . For any current regulator that is detected at
the switchover threshold voltage of 150mV (typ, V IN
falling), internal circuitry switches that current regula-
tor’s return path from GND to NEG to provide enough
voltage across that regulator to overcome dropout
(Figure 5). When V LED_ rises to 250mV (typ), the return
of that current regulator is switched back from NEG to
GND. Each current regulator is independently moni-
tored to detect when switchover is required. Since the
LED current is switched for only the individual LED cur-
rent regulators requiring higher voltage, power con-
sumption is minimized.
REGULATOR
Figure 5. Current Regulator Returning to NEG
LED Dimming Control
The MAX8822 uses a serial-pulse control interface to
program the intensity of the LEDs. The dimming range
is pseudo-logarithmic from 24mA to 0.1mA in 31 steps.
All active LED current regulators are programmed to
the same value, with a 1% (typ) current accuracy and
0.3% current matching between regulators. To program
the LED current, pulse ENLED (500ns to 500μs pulse
width), as shown in Figure 1. An internal register accu-
mulates the pulse count on the rising edge of the
ENLED pulse. See Table 1 for the LED current values
and the corresponding ENLED pulse count. Once the
desired pulse count is met, hold ENLED high for at
least 2.5ms (t HOLD ) to internally latch the pulse-count
value and enable the LED_ current at the programmed
level. If ENLED is pulsed more than 31 times before
latching, the pulse count restarts at 1 on the 32 nd rising
edge. To program a new LED current level, follow the
previous sequence from the beginning. Drive ENLED
low for greater than 2.5ms (typ) to place the LED cur-
rent regulators in shutdown. When the MAX8822 starts
up with ENLED high, the LEDs turn on at full brightness.
If dimming control is not required, ENLED works as a
simple on/off logic control. Drive ENLED high for at
least 2.5ms to enable the LED current regulators, or
drive ENLED low for at least 2.5ms for shutdown. The
LED drivers operate at 100% brightness and off under
these conditions.
10
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相关代理商/技术参数
MAX882C/D
功能描述:低压差稳压器 - LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20
MAX882C/D DIE
制造商:Maxim Integrated Products 功能描述:
MAX882CPA
功能描述:低压差稳压器 - LDO 5/3.3/AdjV 200mA Linear Regulator RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20
MAX882CPA+
功能描述:低压差稳压器 - LDO 5/3.3/AdjV 200mA Linear Regulator RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20
MAX882CSA
功能描述:低压差稳压器 - LDO 5/3.3/AdjV 200mA Linear Regulator RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20
MAX882CSA+
功能描述:低压差稳压器 - LDO 5/3.3/AdjV 200mA Linear Regulator RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20
MAX882CSA+T
功能描述:低压差稳压器 - LDO 5/3.3/AdjV 200mA Linear Regulator RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20
MAX882CSA-T
功能描述:低压差稳压器 - LDO 5/3.3/AdjV 200mA Linear Regulator RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20