Maxim latest LED driver can drive six white light or RGB LED

Maxim Integrated Products recently launched MAX8647 negative charge pump. The innovative negative charge pump architecture eliminates the line impedance between the battery and LED. When the battery is discharged, the circuit is delayed 1 times the pressure to the mode switch between the times of 1.5 times. Proprietary adaptive mode switching technology for six white light or RGB LED independent control. Therefore, even if the LED forward voltage drop (VF) there is a large mismatch, MAX8647 still can greatly improve the efficiency of 12%. This excellent power management program is ideal for use in complex handheld devices that require longer battery life and overall lighting management. Typical applications include cellular phones, smart phones and portable media players, each of which has a very useful battery life (mAh).

The traditional charge pump design limits the efficiency of LED

Ideally, the designer wants to use all of the battery voltage directly under the premise of no loss of efficiency (ie, 1 times the voltage mode without pressure drop) white light and RGB LED. Obviously, to achieve this goal, it is impossible to use a positive charge pump between the battery and the LED. This configuration generates an additional voltage drop in the power supply circuit, which reduces the drive voltage on the LED. When the drive voltage is insufficient, the charge pump opens. As a result, the positive charge pump starts to work with higher battery voltage and reduces efficiency.

The use of 1 times the pressure mode will extend the battery life. However, in order to achieve zero voltage drop, the typical competitive solutions need to remove the positive charge pump, which is impossible for this architecture.

Using the same voltage drive all LED will consume more power

Competitive schemes do not supply power for each LED. The circuit monitors all LED outputs, when any LED current is lower than the preset value, the positive charge pump is switched on. When there is a large mismatch in the forward voltage of the system LED, the highest LED VF will trigger the charge pump to boost the battery voltage. In this way, those with a lower VF corresponding to the current regulator will consume additional voltage and power LED. Therefore, the more VF does not match and the more LED, the greater the power consumption. Video phones, smart phones and multimedia players usually use five or more LED, mismatch problem will further exacerbate the power problem.

Innovative negative charge pump and independent LED switching to solve the problem of efficiency

MAX8647 negative charge pump architecture eliminates the line impedance between the battery and LED. Therefore, when the battery is discharged, the device is delayed 1 times to the switching mode between the voltage and the 1.5 times. Adaptive switching technology for each LED power supply, dimming and steady flow. The final result of this new technology is to improve the efficiency of 12% LED.

MAX8647 negative charge pump built-in adaptive mode switching, with several important advantages. The efficiency is increased by 12%, and the service life of the battery is prolonged. The increase in efficiency is particularly important for cellular phones, as the backlight is a major part of their power dissipation. Higher efficiency has a longer talk time. Accordingly, the use of smaller batteries can achieve the same call time, thereby reducing the cost of the manufacturer. MAX8647 can also replace the inductor boost LED driver, this kind of traditional design often takes up a larger PCB space.

Optimized lighting management

The scope of the application of MAX8647 includes not only the previously mentioned complex handheld devices, but also extended to all display backlight and general lighting management. I2C interface can be controlled for each LED to achieve flexible multi area lighting management, support for 32 levels of brightness adjustment, or the use of RGB LED support 32768 colors. Up to 70 A of quiescent current as well as a dimming current of 100 A (min) will help to achieve the minimum power consumption of "normally open" TFT displays. The device has a current output of up to 1% accuracy, and the battery current is reduced to a minimum when the brightness required for each LED is guaranteed. MAX8647 also has the function of temperature derating and overvoltage protection, which can prolong the service life of LED.

MAX8647's sister product MAX8648 negative charge pump also has adaptive mode switching per LED. The difference is that MAX8648 uses a serial pulse dimming, the LED control is divided into three groups.

MAX8647/8648 uses a miniature 16 pin TQFN package (3mm x 3mm size, 0.8mm high, Max). The device can operate in the extended temperature range of -40 DEG C to +85 DEG C. There are evaluation board (MAX8648EVKIT), can accelerate the design process. MAX8647 starts at $1.95, while MAX8648 starts at $($2500).

Source: Electronic Engineering album