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MAX1916 Datasheet(PDF) 6 Page - Maxim Integrated Products |
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MAX1916 Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 7 page Setting the Output Current SET controls the LED bias current. Current flowing into LED1, LED2, and LED3 is 230 times greater than the current flowing into SET. Set the output current as fol- lows: where VSET = 1.215V, VCTRL is an external voltage between 1.8V and 5.5V, and RSET is the resistor con- nected between VCTRL and SET (Figure 1). Applications Information 1) Very Low-Cost, High-Efficiency Solution (Figure 2). A battery (single Li+ or three NiMH cells) powers the LEDs directly. This is the least expensive and most efficient architecture. Due to the high forward voltage of white LEDs (3.3V), the LED brightness may dim slightly at the end of battery life. The MAX1916’s current-regulating architecture and low dropout greatly minimize this effect compared to using simple ballast resistors. The enable function of the MAX1916 turns on and off the LEDs. An exist- ing low-dropout regulator is used as VCTRL. 2) Brightness Adjustment Using a DAC (Figure 3). A DAC is used as VCTRL such that the LED brightness may be dynamically adjusted to eliminate factory calibration. A battery (single Li+ or three NiMH cells) or a regulated power source drives the LEDs. 3) Existing 5V Supply (Figure 4). Use an existing sys- tem regulator, such as the MAX684, to provide the required LED voltage and provide power to other circuits. Due to the high forward voltage of white LEDs (3.3V), use a 3.6V to 5.5V regulated supply to provide enough voltage headroom such that the LEDs will maintain constant brightness for any bat- tery voltage. Use the existing regulated supply as VCTRL. Chip Information TRANSISTOR COUNT: 220 PROCESS: BiCMOS I VV R LED CTRL SET SET _ () = − 230 Low-Dropout, Constant-Current Triple White LED Bias Supply 6 _______________________________________________________________________________________ MAX1916 ON EN OFF EXISTING LDO GND SET LED1 LED2 LED3 VCTRL V+ TO OTHER CIRCUITS Figure 2. Very Low-Cost, High-Efficiency Solution MAX1916 ON EN OFF DAC GND SET LED1 LED2 LED3 VCTRL V+ Figure 3. Brightness Adjust Using DAC MAX1916 ON EN OFF EXISTING REGULATOR GND SET LED1 LED2 LED3 VBATT V+ 5.0V TO OTHER CIRCUITS Figure 4. Existing 5V Supply Circuit |
Similar Part No. - MAX1916 |
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Similar Description - MAX1916 |
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