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ADP8866 queries

Question asked by Asad on Feb 1, 2012
Latest reply on Oct 10, 2012 by Asad

I am reading the datasheet of ADP8866 for designing a solution. On pg.14, under the title 'LED groups', reference is made to I2C data registers 0x9 and 0xA for selecting/forming an LED group. Subsequently, on pg.28, under the PWR_SEL1 (0x09) and PWR_SEL2 (0x0A) register details, bit state 1 indicates 'LED powered from battery or other power source' while bit state 0 indicates 'LED is powered from the charge pump' which is Vout pin. This is very confusing and ambiguous. The datasheet is vague on this and certain other issues.

 

Is the LED group selection based on the power source? Is the use of the charge pump optional? The IC description makes no clarification about this. Design wise, is it be possible to connect the LEDs (anodes) to the positive battery terminal while the cathode is connected to the D1-D9 pins? Will the ADP8866 still regulate the current as set in the current control related registers? If possible, what kind of energy saving could one expect when the Vout switch resistance is not in series to the LED anode(s) and the charge pump isn't needed/used? Carrying on, would the charge pump capacitors still be needed or can they be omitted from the design?

 

Also, what is the difference between the options for the backlight and independent sink control options? In which case would one go for one over the other? In my application, I have 8 LEDs of Vf=2.5V, If=20mA connected to D1-D8. Their blinking patterns are synchronized (all turn on/off at the same time). Which of; backlight or ISC, is the recommended method for my application?

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