ICs drive up to 6 white or RGB LEDs.
Press Release Summary:
Suited for complex handheld devices, Models MAX8647 and MAX8648 have negative charge pump architecture, adaptive-mode switching, and -40 to +85°C operating temperature range. With 70 µA quiescent current and 100 µA minimum dimming current, Model MAX8647 features LED controller I2C interface that enables multizone light management for up to 32 brightness levels, or 32,768 colors with RGB LEDs. Model MAX8648 groups control of LEDs into 3 zones with serial-pulse dimming.
Original Press Release:
Negative Charge Pump Achieves Industry's Highest Efficiency for Driving up to Six White/RGB LEDs for Light Management
The MAX8647/MAX8648 are negative charge pumps that provide the highest efficiency for driving up to six white or RGB LEDs for display backlights and general light management.
A unique, negative charge pump architecture and innovative adaptive-mode switching for each LED realize an impressive 12% efficiency gain, even with a large LED forward voltage (VF) mismatch.
Devices are ideal for complex handheld devices requiring long battery life and total light-management flexibility like cell phones, smartphones, and media players.
SUNNYVALE, CA-June 20, 2007-Maxim Integrated Products (NASDAQ: MXIM) introduces the MAX8647, a negative charge pump that provides the industry's highest efficiency in powering LCD display backlights. An innovative, 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 achieves a significant 12% boost in efficiency, even with large LED forward-voltage (VF) mismatch. This superior power management is ideal 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 milliamp-hour (mAh) of battery life is paramount.
Conventional Pump Design Limits LED Efficiency
Ideally, designers want to directly drive (i.e., 1x mode with no voltage drop) white and RGB LEDs for all battery voltages without losing any efficiency. However straightforward this objective, it has not been possible to achieve with "positive" charge pumps, which are located between the battery and LED. This configuration forms an undesirable dropout along the power line, causing a lower driving voltage to the LEDs. The charge pump turns on whenever the driving voltage is inadequate. As a result, the positive charge pump starts operating at higher battery voltages, leading to very poor efficiency.
Staying in 1x mode longer extends battery life. But to achieve zero dropout, typical competitive approaches need to remove the positive charge pump, an impossible task with such an architecture.
Applying the Same Voltage to All LEDs Wastes More Power
Competing solutions do not supply voltage to LEDs individually. Rather the circuit monitors all LED outputs and switches on the positive charge pump as soon as any one LED current falls below predetermined level. If the system exhibits large LED forward-voltage mismatch, the highest LED VF triggers the charge pump to boost up from the battery voltage. Simultaneously, for those LEDs with lower VF, the corresponding current regulators dissipate the excessive voltage and power. Consequently, the more the VF mismatch and the larger the number of LEDs, the more power is wasted. TV-phone, smartphones, and multimedia players use five or more LEDs, so the mismatch problem exacerbates the efficiency loss.
Innovative Negative Charge Pump and Individual LED Switching Solves Efficiency Dilemma
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 innovative technology is a 12% increase in LED efficiency.
The MAX8647 negative charge pump with adaptive-mode switching delivers 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.
Optimized Light Management
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°C to +85°C extended temperature range. An evaluation kit (MAX8648EVKIT) is available to speed design. Prices start at $1.95 for the MAX8647, and $1.70 for the MAX8648 (2500-up FOB, USA).
For more information please visit: http://www.maxim-ic.com/Negative-Charge-Pump
