Look at the diagram on page 8 of the datasheet.You see a voltage divider (string of 1k resistors) inside the chip.One end of the string is connected to a reference voltage, and the other end (normally) to ground.R2 in your diagram increases the value of the bottom resistor to 18k+1k= 19k.That "lifts" the reference voltage on the lowest opamp (first LED) to 19/(19+9) * Vref, or ~68%.Note that the chip will overheat/shutdown of you power it from 12volt and drive more than a few LEDs.12volt LED power is ok in dot mode, but not in bar mode.Leo..
In the string of comparators, are the comparators the same value or how does it not activate them all at once.
For my r2 resistor, where does the extra 1k come from?
Also im still not 100% positive what the reference voltage does?
Reference voltage is divided equally over the string of 1k resistors.10% on the first tap, 20% on the next tap, 30% on the next, etc.The comparators each compare input voltage (the battery) to the voltage on their tap.If a comparator senses that input voltage is higher than their tap voltage, the corresponding LED is turned on.It should be clear that the comparator with the lowest tap voltage is the first to turn on when input voltage rises.There is already a 1k resistor between the string and RLo (pin4).Adding 18k between Rlow and ground will turn that 1k resistor into a 19k resistor.Think old fashioned balance scales.You put a calibrated weight on one side (the reference) and the product on the other side.When it tips, then you know the product is heavier than the reference.Leo..
Hi - This is exactly what I need as well. I managed to get the basic range of 0V-5V working but anything below 3V not much help when you use LiPo as PSU.Did you manage to calculate the values for R1 and R2 to get voltage range of 3V to 4.2V? I would sincerely appreciate your help. Regards,Friedl.
Not a typo.4.1 - 1.25 = 2.85In your diagram, 1.25volt is across the 3k3 resistor,so (2.2 + 3.3) / 3.3 * 1.25volt = 2.08volt is on Rhi.Not what you want for a LiPo battery.1k2 for R2 and 2k7 for R1 comes close.(1.2 + 2.7) / 1.2 * 1.25 = 4.0625volt on Rhi, and 1.25/1k2 * 10 = ~10.4mA LED current.Leo..