Nippon Precision Circuits, Inc. (NPC)* has begun a sample shipment of the white LED driver, the "SM8122AH", that has an output overvoltage protection circuit to reduce to need for additional components.

Recently, portable devices such as cell phones, digital still cameras, PDAs (Personal Digital Assistants) and the like have spread rapidly. These portable devices have come to generally use a white LED as the back light for colored Liquid Crystal Display (LCD) panels. In addition, there are many requirements for the reduction of luminance variations for LEDs, high efficiency, low power consumption and compactness to the white LED drive ICs due to the growing desire of users for improved functions and performance of these devices.
In the released SM8122AH, an output overvoltage protection circuit is incorporated to cut the need for additional external Zener diodes for this circuit. Since the SM8122AH also has low inductance and has a small outward form, the switching frequency of a coil has reached 2MHz which is twice the equivalent as the conventional SM8121AH. With the use of the SM8122AH, you can easily obtain a highly-efficient and highly-precise white LED drive without placing a burden on the circuit designers.
This device has the following features:

- Power efficiency
The SM8122AH uses a switching regulator system that has high power efficiency and it has obtained a highly-efficient white LED drive that is 85% superiority by satisfying both needs for the high-speed switching and current consumption reduction. Since this device can obtain a 25V output voltage, it can light two to six white LEDs connected serially.

- Variations of LED luminance
The SM8122AH has reduced the variations of LED luminance with the following two methods:
Firstly, a serial connection of LEDs perfectly eliminates the variations of a relative current between LEDs.
Secondly, the high-precision procedure of a reference voltage has successfully suppressed to +/-2.0% of the error detected by an LED current. If a resistor having the absolute resistance of +/-0.5% in an external LED current setting resistor is used, the current of all the LEDs can be controlled with the absolute precision of +/-2.5%. This is accomplished by adding the absolute current detection error of +/-2.0%, which contributes to suppress the LED luminance variations at the time of mass production.

- Pressurization control
A pulse width modulation (PWM) has been used in pressurization control. The PWM is a method that controls an LED current by changing switching pulses with the changes of an input voltage and output load (LED current.) With this, even if the input current changes, an average value of the LED current will remain stable.

- Reduced number of components and smaller mounting area
With incorporating the output overvoltage protection circuit, the Zener diodes mounted outside the output overvoltage protection circuit will be unnecessary. The SM8122AH can use low inductance and it has a small outward form thanks to being 2MHz of the switching frequency of a coil. The SM8122AH has obtained a white LED drive by reducing the number of components in a smaller mounting area than ever.
This device uses a small package containing the SOT23-6 pins and its external dimensions have been reduced to 3.0 x 3.1 mm at maximum. The Zener diodes have been successfully eliminated for the output overvoltage protection from necessary external components. Eliminating the Zener diodes allows the white LED drive circuit to be mounted even in a narrow and limited mounting area by using one coil, one rectification diode, two capacitors and one resistor.

NPC plans to develop a series of products that apply these element technologies in the future.

* Main Office: 4-3, Fukuzumi 2-chome, Koto-ku, Tokyo; President: Yoshifumi Gomi

Product Name	Shipping of Sample	Sample Price (Tax included)	Mass production shipment	Mass production plans
SM8122AH	November, 2004	200 yen/unit (210 yen/unit)	January, 2005	1 million/month