Charge Pump Driver for 6 White LED LCD Backlights
To maximize power efficiency, the charge pump can operate in a 1×, 1.5×, or 2× mode. The charge pump automatically switches between 1×/1.5×/2× modes, based on the input voltage, to maintain sufficient drive for the LED anodes at the highest power efficiency
Improved brightness matching of the LEDs is achieved by a feedback pin to sense individual LED current with a maximum matching accuracy of 1%.
- Cellular phones with main and sub displays
- White LED backlighting
- Camera flash/strobes and movie lights
- Micro TFT color displays
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At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
- ADM8845 Evaluation Board
- PC Parallel to Serial Cable
- CD containing evaluation board software
The ADM8845 evaluation board contains the following main components, which can be identified from the block diagram, the schematic diagram and the printed circuit board.
- 13 jumper points to facilitate the connection of external inputs and internal circuitry.
- 21 test points for signal connection and measurement
- A patchwork area to facilitate the connection up the ADM8845 Eval Board to external components.
The ADM8845 provides the power required to drive up to 6 white LEDs, using charge pump technology. The LEDs are used for backlighting a color LCD display. To maximize power efficiency, a charge pump that can operate in either a 1x, 1.5x or 2x mode is used. The charge pump automatically switches between 1x/1.5x/2x modes based on the input voltage, to maintain correct output levels at a high power efficiency. Improved brightness matching of the LEDs is achieved by the use of a feedback pin to sense individual LED current with a maximum ILED to ILED matching accuracy of 1% and ILED to ISET maximum matching of 1%.
The ADM8845 provides two digital input control pins, CTRL1 and CTRL2, which control the operation and the brightness of the LEDs. The ADM8845 is configured with a sub and main display, the main display refers to 4 of the 6 LEDs (FB1 - FB4) and the sub display refers to the remaining 2 LEDs (FB5 – FB6).
The ADM8845 provides the option to control the brightness of the LEDs with a digital PWM signal. The duty cycle of the PWM signal determines the brightness of the backlight LEDs. Brightness control of the LEDs can also be controlled by a DC voltage. The ADM8845 has soft-start circuitry to limit inrush current flow at power up.
The ADM8845 is fabricated using CMOS technology for minimal power consumption. The part is packaged in a 16-lead LFCSP (Lead Frame Chip Scale Package).
Solutions Bulletins & Brochures
Charge Pumps Products (March 2003)
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