Power Electronics

Charge Pumps Power WLED Flashes

Maxim Integrated Products introduces the MAX1577Z/MAX1577Y, high-efficiency 1x/2x charge pumps, which can drive white LEDs with regulated current up to 1.1 A (800 mA guaranteed). By using a proprietary adaptive-mode switching technique, the charge pumps provide high efficiency (up to 92%) in movie mode or backlighting. The very-low, open-loop output resistance allows the highest WLED flash brightness, even from a low-battery input voltage.

Requiring only three tiny ceramic capacitors, these devices eliminate the need for a step-up dc-dc converter and low-profile inductor, which ensures that the parts meet the height constraints in clamshell cell phones. Fast 1-MHz switching allows the use of tiny external components. The regulation scheme is optimized to ensure low EMI and low input ripple.

The MAX1577Z/MAX1577Y uses an external resistor to set the full-scale LED current. Two enable inputs (EN1 and EN2) provide simple on/off control and LED current of 20%, 33% or 100% full-scale. The charge pumps also feature soft-start to limit inrush current, thermal-shutdown, and complete input-to-output disconnect during shutdown (0.1 µA shutdown current). The input voltage range is 2.7 V to 5.5 V. The MAX1577Z has fixed 5.1-V output overvoltage protection. The MAX1577Y has logic-controlled output current for flash, and 3.4-V, 4.6-V or 5.1-V output voltages for backlight, keyboard and RGB applications.

The MAX1577Z/MAX1577Y are available in a space-saving, 8-pin, 3-mm × 3-mm TDFN package, screened for the industrial temperature range (-40°C to 85°C). Prices start at $1.80 (2500-up, FOB USA).

For more information, visit www.maxim-ic.com.

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