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Phase-shifted LED backlight driver supports ultra-thin notebooks LCD panels for the first time

September 02, 2011 // Paul Buckley

Phase-shifted LED backlight driver supports ultra-thin notebooks LCD panels for the first time

Semtech Corp., has launched the first device in its innovative platform of phase-shifted boost LED drivers. The new SC5010 is an 8-channel white LED driver with an innovative PWM phase-shift dimming control that uses low-profile inductors, allowing LED drivers to be built directly into the LCD panel in Ultrabook PCs and ultra-mobile PCs (UMPC) for displays as thin as 4 mm.

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The device also enables ultra-thin LCD displays with longer battery life in tablet, automotive, and other mid-size display applications.

The SC5010 delivers higher efficiency when using the same size inductors as existing phase-shifted LED drivers, but unlike these devices, the SC5010 can operate with inductors that are up to 10X smaller while maintaining high efficiency. This enables LED drivers to be designed directly into the panel, even in ultra-thin applications. This is due to the sophisticated control loop architecture, which allows the use of inductors as small as 2.2 H (1mm height). The phase-shifted technology in the SC5010 also minimizes demand on the input and output capacitance offering the high efficiency of conventional non-phase shifted switching regulators, with significantly lower noise, less EMI, and no need for noise filtering components.

The SC5010 is an 8-channel boost LED driver that can power up to 112 LEDs, with currents up to 30 mA per channel. The integrated control loop architecture of the device allows programmable switching frequencies as fast as 2.2 MHz and is the key to enabling phase-shifted dimming using small, low-profile inductors. Additionally, this approach reduces BOM size and cost by eliminating external compensation and noise filtering components.

Semtechs innovative loop architecture also prevents display flicker and shutdown caused by line transients that can occur in automotive applications. This is achieved via the ultra-fast transient response of the SC5010, which allows it to handle line transients up to 10 V/s.

The SC5010 LED driver brings to market a rich feature set for the next generation of displays, including the flexibility of I2C and three PWM dimming control modes. It features a wide PWM input dimming range of 5000:1 at 200 Hz and a dimming frequency range from 100 Hz to 30 kHz. The SC5010 also provides user-selectable 9 or 10 bit dimming resolution and a 5-bit analog dimming register that can be used in conjunction with PWM to increase the dimming resolution.

The phase shifted PWM dimming turns the LED strings on and off at the same frequency and the same duty cycle, but at different and equally spaced, automatically calculated phases. This reduces demand on the input/output capacitance to decrease radiated switching current, which improves EMI performance and dimming linearity.

The SC5010 delivers accurate backlight color temperature and uniform brightness across the entire display, with 1% channel-to-channel current matching and accuracy of 1.5%. Full protection functions include open LED and programmable shorted LED, adjustable over-voltage (OVP), and over-temperature protections; as well as under-voltage lock out (UVLO) shutdown.

The SC5010 is available immediately in production quantities and is priced at $1.20 each in 3,000-piece lots. The ordering code is SC5010ULTRT. Evaluation boards (SC5010EVB) are also available.

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