6-channel LED driver with digital control engine addresses mid to large-size LCD TVs

March 01, 2013 // By Christoph Hammerschmidt
With the iW7011, power management chip provider iWatt introduced a 6-channel LED driver with a built-in intelligent digital control engine, developed to reduce the bill of materials (BOM) cost and simplify design of edge-lit and direct-lit LCD TVs.

The digital core of the iW7011 provides on-chip control of the DC-to-DC boost circuit, along with precise LED dimming control and all the monitoring and feedback for the LED drivers. It also allows timing delays to be set for dynamic scanning, simplifying design by enabling one part to be used for both 2D and 3D TVs. The iW7011 uses external LED current sinks and external boost MOSFETs for easy current and voltage scaling (up to 300mA per channel and Vout close to 85V), allowing designers to source one part type to meet requirements spanning medium- to large-size LCD TVs and monitors.

The iW7011 lowers BOM costs by integrating a number of design features. The on-board boost controller provides a high-voltage power supply for external LED strings. The digital control engine allows real-time control of phase delays (especially relevant for 3D TVs) and manages Vsync synchronization (from 50Hz to 480Hz) and fault read outs, eliminating costly microcontrollers. Additionally, the iW7011 offers an 85V capability on drain sensing, which means there is no need for cascodes or zener clamps for protection, while high-voltage drain sensing eliminates external diodes usually required for LED short-circuit fault management.

The digital control engine in the iW7011 improves overall system efficiency by optimizing the DC-to-DC voltage based on the minimum feedback voltage of the LED strings that is required to maintain the target current regulation. The digital control engine also generates the current sink PWM waveforms, processes the fault conditions, and reports on all faults.

The iW7011 enables dimming control, with 14-bit resolution at 120Hz PWM frequency. It offers the flexibility of phase-shifted dimming of the current sinks either through direct PWM mode or through an SPI interface. Additionally, an optional 8-bit analog register can be used to increase the dimming resolution. Phase-shifted dimming reduces capacitance demand on the input and output to improve both dimming linearity and EMI (electromagnetic interference) performance. Four phase-shift dimming options are