I needed a 20x4 character LCD module for my project, and this one is a good match. However, when reading the data sheet, I can't figure out what NewHaven is doing with the backlight.
Typically, the LED backlight is either a direct connection to a string of LEDs, or has onboard current limiting (via a resistor or a current regulator.) The diagram on page 4 of the PDF shows that the LED-A should be connected directly to the supply, and LED-K should be connected to 0V. This implies that the backlight is current-limited.
However, the supply voltage doesn't make much sense to me. The module wants to be powered at 3.3V, +/- 200mV. OK, that's a pretty tight tolerance, but sure, no problem. OTOH, the LED wants 3.0V, +/- 200mV. Uh, wait... 3 point ZERO volts? I don't get it.
If there's an onboard regulator, is it REALLY so marginal that it can't hang with a common 3.3V supply? If it's a current-limiting resistor, was its value selected to be at the very threshold of reliability at 3.2V, such that it can't handle another 100mA? More to the point, why doesn't the data sheet give some clue as to what the backlight circuit IS? If I knew it was a couple strings of 2 series 1.4V fwd-drop LEDs with 0.01R balancing resistors, I could make some educated engineering decisions...
Also, 280mA supply current for the backlight? Holy geez, how bright is that thing??
None of this adds up to what I'm used to with typical LCD modules, so I'm really not sure what the correct solution would be. Do I actually need a 1W-capable buck regulator to drop 300mV on my supply rail? Or is that an order-of-magnitude typo and I need to add a limiting resistor selected for 28mA with a fwd drop of 3.0V? If so, why does the data sheet not show this in the diagram? (It even went to the trouble of showing the contrast potentiometer -- with recommended values!)
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