Maxim Negative Charge Pump Drives Up to 6 White/RGB LEDs for Light Management

Maxim Integrated Products introduced the MAX8647, a negative charge pump that provides what the company claims is the industry’s highest efficiency in powering LCD display backlights. The negative charge-pump architecture eliminates in-line resistance from battery to LEDs. This design delays mode switching from 1x to 1.5x during battery discharge. A proprietary, adaptive-mode switching technology controls each of the six white or RGB LEDs independently. As a result, the MAX8647 is said to achieve a significant 12% boost in efficiency, even with large LED forward-voltage (Vf) mismatch. This power management is well-suited for complex handheld devices that need long battery life and benefit from total light management. Typical applications are cell phones, smartphones, and portable media players where every mAh of battery life is paramount.

The MAX8647’s negative charge-pump architecture eliminates in-line resistance from battery to LEDs. As a result, mode switching from 1x to 1.5x is delayed during battery discharge. The adaptive-mode switching technology supplies, dims, and regulates each LED individually. The net result of this technology is said to be a 12% increase in LED efficiency.

The MAX8647 negative charge pump with adaptive-mode switching is claimed to deliver several important benefits. The additional 12% efficiency extends battery life. This extra efficiency is especially important for cell phones, where backlight is a major power-consuming function. Greater system efficiency leads to proportionally longer talk-time. Moreover, a smaller battery can achieve the same talk-time, so the manufacturer will reduce costs. The MAX8647 can also replace the inductor-boost LED drivers which consume a large piece of PCB estate in conventional designs.

The MAX8647’s applications extend beyond the complex handheld devices noted above to any display backlights and general light management. An I2C interface controls each LED that enables multizone, "fun" light management for up to 32 brightness levels, or 32,768 colors with RGB LEDs. The low 70µA quiescent current and the 100µA (min) dimming current facilitate "always-on" TFT displays that require minimal power. Highly accurate, ±1% current accuracy draws minimum battery current for each LED’s required brightness. The MAX8647 also features temperature derating and overvoltage protection to extend the life of the LEDs.

A sister product to the MAX8647, the MAX8648 negative charge pump also has adaptive-mode switching to each LED. Uniquely, the MAX8648 groups the control of the LEDs into three zones with serial-pulse dimming.

The MAX8647/8648 are available in a tiny 16-pin TQFN (3mm x 3mm footprint, 0.8mm height, max). They are screened for the -40 +85°C extended temperature range. An evaluation kit (MAX8648 EV Kit) is available to speed design. Prices start at $1.95 for the MAX8647, and $1.70 for the MAX8648 (2500-up FOB, USA).