Analog Devices ( http:// ) ADM8845 provides the power required to drive up to 6 white LEDs from a 2.6 V to 5.5 V (li-ion) input supply, using charge pump technology. The white LEDs are used For backlighting a color LCD display.
To charge power efficiency, a charge pump that can operate in either of 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 white LEDs is achieved by the use of a feedback pin to sense each individual LED current with a maximum matching accuracy of 1% and ISET to ILED maximum matching of 1%.
The ADM8845 provides two digital input control pins, CTRL1 and CTRL2, which control the shutdown operation and the brightness of the LEDs. The LEDs are arranged into two groups, main and sub display options, the main display refers to 4 of the 6 LEDs ( FB1 -FB4) and the sub display refers to the remaining 2 LEDs (FB5 - FB6).
Brightness control of the white LEDs can be achieved with a digital PWM signal applied to CTRL1 and/or CTRL2 to provide brightness control on the main and/or sub displays. The duty cycle of the applied digital PWM signal determines the brightness of the backlight white LEDs. Also brightness control of the white LEDs can be controlled using a DC voltage or a PWM signal applied to the ISET pin with a few external components added.
The ADM8845 also has soft-start circuitry to limit inrush current flow at power up. It is fabricated using CMOS technology for minimal power consumption. The part is packaged in a 16-pin LFCSP package.
To charge power efficiency, a charge pump that can operate in either of 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 white LEDs is achieved by the use of a feedback pin to sense each individual LED current with a maximum matching accuracy of 1% and ISET to ILED maximum matching of 1%.
The ADM8845 provides two digital input control pins, CTRL1 and CTRL2, which control the shutdown operation and the brightness of the LEDs. The LEDs are arranged into two groups, main and sub display options, the main display refers to 4 of the 6 LEDs ( FB1 -FB4) and the sub display refers to the remaining 2 LEDs (FB5 - FB6).
Brightness control of the white LEDs can be achieved with a digital PWM signal applied to CTRL1 and/or CTRL2 to provide brightness control on the main and/or sub displays. The duty cycle of the applied digital PWM signal determines the brightness of the backlight white LEDs. Also brightness control of the white LEDs can be controlled using a DC voltage or a PWM signal applied to the ISET pin with a few external components added.
The ADM8845 also has soft-start circuitry to limit inrush current flow at power up. It is fabricated using CMOS technology for minimal power consumption. The part is packaged in a 16-pin LFCSP package.
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