OZ976

The Phase Array (OZ972/OZ976) is a unique, high-efficiency, CCFL backlight controller chipset that is targeted for LCD applications requiring 6 to 48 lamps. The Phase Array chipset consists of two devices, the OZ976 Array Hub and OZ972 Power Controller. Depending on the number of lamps, each application requires one OZ976 device and either 6, 8, 10 or 12 OZ972 Power Drivers. The number of OZ972 devices used in an application is user-selectable. Figure 1, page 8, illustrates the Phase Array topology.

The OZ972, Power Controller, drives a zerovoltage- switching full-bridge circuit, providing output voltage and current waveforms to the CCFLs. Operating in a zero-voltage switching configuration; the inverter circuit minimizes EMI emission. In addition, the inverter circuit achieves very high power conversion efficiency resulting in lower heat and higher system reliability. A smart protection circuit is incorporated in the Power Controller to achieve a high safety requirement. This circuit provides lamp ignition, normal operation, open lamp and broken lamp protection, and communicates the status to the OZ976. Intelligent open-lamp and over-voltage protection provides design flexibility with various transformer characteristics.

The OZ976, Array Hub, generates and distributes the operating frequency to all OZ972 Power Controllers, to ensure that all lamps operate at one frequency. This eliminates interference among lamps that result from different lamp operation frequencies. Interference causes EMI problems and may create visual effects (waterfall) on the LCD panel. The operating frequency of the OZ976 is programmable via an external resistor and capacitor.

The OZ976 utilizes the pulse-width-modulation (PWM) dimming method to achieve a wide dimming range. The PWM dimming frequency can be synchronized with an external TTL-level signal or an internal signal, programmed via an internal (LCT) oscillator circuit. If an external TTL level signal does not exist, the OZ976 will automatically follow the pre-programmed LCT frequency to generate the PWM signals. Otherwise, the external TTL level frequency will be used to generate the PWM signals.

The OZ976 provides a set of PWM signals with a different phase delay to each OZ972. This method reduces power supply ripple. Without the PWM phase shift, a system utilizing a large number of lamps, for example 12, would cause a large power supply current surge (spike) if the lamps turned on and off simultaneously. This abrupt power demand increases the power supply design burden and degrades EMI performance. By splitting a large power demand into smaller segments, the OZ976 minimizes the peak power bus ripple and in-rush current. The OZ976 monitors the power supply voltage to prevent an under-voltage lockout condition. OZ976 will disable all the inverters if it detects an under-voltage condition.

The OZ972 is available in a 16-pin SOP package and the OZ976 in a 48-pin LQFP package. Both devices are specified over the commercial temperature range from 0oC to 70oC, and the industrial temperature from -40 to 85.