Product News I LED Technology
16-channel LED backlight driver delivers enhanced TV picture quality
Dialog Semiconductor has unveiled the iW7025, a 16- channel LED backlight driver that supplies enhanced picture quality, patented short protection and lower cost for next- generation 2D and 3D LCD TVs. Dialog’s patented AnyMode dimming gives TV OEMs a comprehensive dimming option that will improve picture quality and an extensive set of short protection features to prevent circuit failures and safety issues. A key challenge for LED TV designers is how to easily reduce motion blur and deliver a high contrast ratio. Conventional LED drivers require complex
calculations and algorithms to configure the LED current phases to optimally synchronise the LCD panel backlight to the video frame refresh rate. The iW7025’s AnyMode dimming solves this by providing comprehensive, simple and flexible dimming options that improve LED TV picture quality and reduce design complexity. These dimming modes include high frequency pulse width modulation (PWM) up to 4kHz, scanning- mode PWM, configurable phase-shift, 8-bit analogue, 13-bit local and hybrid dimming. AnyMode dimming enables continuous PWM signals or burst PWM signals that are fully synchronised to the video frame at the same or higher frequency. The PWM duty cycle can be updated in each video frame and with user- configurable tail or head delays giving designers more options to reduce motion blur and improve the contrast ratio. A built-in phase-locked loop (PLL) further ensures jitter-free operation even with a noisy VSYNC signal. The iW7025 also incorporates robust short detection and protection features including: individual LED short, channel-to-channel short, current sink MOSFET drain-to-source short, bipolar junction transistor (BJT) collector-to- emitter short, current sense resistor short, and chip-to-chip string short protection across multiple LED drivers. LED open-fault detection and over-temperature protection are also included.
The iW7025 uses external LED current sinks and up to two external DC converters (boost,
buck, LLC, etc.) for the LED driver to enable easy current and voltage scaling (600mA or more per channel and Vout to 85V maximum). This allows designers to source one part type to meet requirements spanning medium- to large-size LCD TVs and monitors. The iW7025 reduces the bill of materials (BOM) cost in a number of ways including the need for expensive microcontrollers and it supports lower cost BJTs for further BOM cost savings.
The PWM dimming range of the iW7025 is 0% to 100%, with 13-bit resolution. Precise control of the PWM output position and the PWM duty cycle offer the flexibility to support both patterned retarder (PR) and shutter glass (SG) 3D technologies, while hybrid dimming lets users mix PWM and analogue dimming modes to maximise system efficiency. Phase-shift dimming allows the use of smaller output capacitors, eliminating audible noise, improving electromagnetic interference (EMI), and lowering cost.
The iW7025 provides high, ±2% channel-to- channel matching accuracy and ±0.5% absolute current accuracy to deliver uniform brightness across the entire display. It comes in two package options: a 64-pin, 10mm x 10mm, thin QFP with 0.5mm pitch and a 64-pin, 14mm x 14mm, thin QFP with 0.8mm pitch, both with pin-outs optimised for single-layer PCB layout.
Dialog Semiconductor |
www.dialog-semiconductor.com
Diode’s LED driver enables high power factor retrofit LED lamps
Diodes Incorporated has unveiled the AP1684, a power factor- corrected AC-DC LED driver that suits a variety of offline LED lamp types, including E26, GU10, PAR and T8. Using pulse-frequency modulation technology and operating in boundary- conduction mode, this device provides tight current regulation to an accuracy of ±2%, while achieving a power factor of .97 and THD of less than 20%. Helping to significantly reduce
circuit BOM cost, this primary- side driver removes the need for opto-coupler, secondary-side control and loop-compensation circuitry. Driving an external bipolar junction transistor, the AP1684 requires only a small external component count and coupled with its SO8 packaging, enables lamp designers to reduce PCB footprint, increase power density and raise overall product reliability. The driver keeps start-up and operating
currents low and uses dynamic base driver control and valley-mode switching to minimise
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transition loss and achieve high efficiency, typically 93%. The AP1684’s circuit protection features are comprehensive and include over- voltage, short-circuit and over-temperature facilities.
Diodes Incorporated |
www.diodes.com Components in Electronics November 2013 23
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