SSD1327 LED driving voltage - Page 1
Forum section: electronics / projects

author: datasheet
author_rank: Newbie
timestamp: June 27, 2021, 05:28:52 pm
content: I'm planning on buying a SSD1327-based OLED panel. The SSD1327 datasheet (link) indicates that the needed driving voltage VCC must be between 8V and 18V. Unlike the SSD1306, the IC doesn't include a charge pump, so I'll need a boost converter.Does anyone know what impact the driving voltage will have on the display? It seems like a pretty big range so I'm not sure. Looking at the LED driving circuit on Figure 8-11 in the linked datasheet, it looks like it is current-controlled (using Iref), so it shouldn't have an impact right? For reference, the SSD1306 requires a VCC range of 7V-15V and the internal charge pump generates a 7.5V voltage, so my first impression is that 9V is going to be fine. Yet, I've seen a schematic by an open hardware company that used 15V for a similar display with the same controller.I'm asking because it's going to influence my choice of a boost converter IC. If I need 15V, not all of them support it. Also a boost converter outputting 15V from a a 3V supply is going to be somewhat less efficient than one outputting 9V, and efficiency matters in my case.This is probably very dependent on how the rest of the display is built, so I asked the distributor, but I fear I'm going to get the typical reply of the Chinese distributor that doesn't have a clue what they're selling. (it's BuyDisplay in case anyone has experience with them)

author: floobydust
author_rank: Super Contributor
timestamp: June 27, 2021, 07:08:22 pm
content: Welcome to the forum!The raw OLED panel will have a driving voltage spec, such as 12V for 2.4". It varies between panels and their size/colour. You will have to check your particular OLED panel's datasheet.The controller IC needs to work with that, that is the range given on the IC datasheet- but is not the panel's required voltage.Always look for the latest and greatest OLED controller datasheet, Generation Robots is old 2008 Ver. 1.1 but2013 1.8I see out there. Lots of bug fixes and nobody likes a blank display due to a bad datasheet.You can look at the schematics for the module boards that include the boost converter, to see what they have done with your chosen panel. Typically a little SOT23 boost-converter and the resistors to set mode and OLED current.I think the controller IC's can get damaged if the HV is up but the logic power is not, i.e. 12V present but not 3.3V so I put a diode there between the rails to prevent backfeed during power up/down. The SSD1327 mentions having an ESD diode there so there is coverage at lower current. Just keep the capacitors the smaller recommended value on the HV rail.I was surprised about the price increases and notification:※ Price Increase Notification"The TFT glass cell makers such as Tianma, Hanstar, BOE, Innolux has reduced or stopped the production of small and medium-sized tft glass cell from August-2020 due to the low profit and focus on the size of LCD TV, Tablet PC and Smart Phone. It results the glass cell price in the market is extremely high, and the same situation happens in IC industry. We deeply regret that rapidly rising costs for glass cell and controller IC necessitate our raising the price of tft display. We have made every attempt to avoid the increase, we could accept no profit from the beginning, but the price is going up frequently,we're now losing a lot of money. We have no choice if we want to survive. There is no certain answer for when the price would go back to the normal. We guess it will take at least 6 months until these glass cell and semiconductor manufacturing companies recover the production schedule. (Jun-21-2021)"

author: datasheet
author_rank: Newbie
timestamp: June 27, 2021, 07:42:32 pm
content: Oh actually they do indicate the voltage in the datasheet! I totally missed it. It's 15V. Here's alink to the display page. I thank you nonetheless for the reply, it's very informative!A weird thing I also just found is that, in the panel's description, they say: "The controller ic SSD1327, communicates via I2C,4-Wire SPI Serial or 8080/6800 8-bit Parallel,, interface,thanks to controller's built-in voltage generation,only a single 3.3V power supply is needed." There's no such voltage generation in the controller, at least not for the VCC rail. A copy paste error from a SSD1306 panel perhaps?Quote from: floobydust on June 27, 2021, 07:08:22 pmI couldn't see the notification so I googled the message, found this old thread from 2016, with the exact same message:https://www.eevblog.com/forum/projects/small-tft-lcd-price-rises/Gotta save on the English translators I guess. There are shortages of a lot of things these days so not too surprising.

author: floobydust
author_rank: Super Contributor
timestamp: June 27, 2021, 08:08:27 pm
content: Way too much is lost in translation, you have to find the raw panel manufacturer and triple check.Many of the display companies are just middlemen, cut and pasting datasheets and making a royal mess.It looks like you need14.5VDC 24mA 50% pixels onand EastRising spec 15VDC at 0.12mA seems out to lunch, that must be just the IC's current not the OLED.Some controller IC's have a charge-pump to make moderate HV so you add a bunch of capacitors and don't need a boost converter, or they are referring to the module board which includes one.FAN5331does OK.

author: datasheet
author_rank: Newbie
timestamp: June 27, 2021, 10:58:52 pm
content: The operating currents in the EastRising datasheet are totally off, I think they were salvaged from the page 53 of the SSD1327 datasheet since they're identical. That page says "Conditions: VCI = 3.5V, VCC = 18V, Display ON, No panel attached, contrast = FF". As you said, just the controller IC, not the panel.As for the raw panel origin, my bet would be on RiTdisplay. They claim to have done R&D on OLED in theirabout pageand they're manufacturing panels. The open hardware company I mentioned earlier used a module from them (datasheet), there's even a few images that match the EastRising datasheet. The dimensions are identical. The copy-pasted feel is much less worse for that datasheet too. Unfortunately RiTDisplay does not seem to be selling to individuals. Between that and what you found, I think I can safely settle on 15V.I had already found a boost converter IC,MIC2250, it looks very similar to the one you proposed so it should be fine. I'm not too sure about the current consumption for the display though. For example,this guyreports a 147mA@3.3V current consumption for a similar display, all pixels on but only 20% contrast! I can't see why it would be much higher than double of what a similarly sized 128x64 panel uses i.e. ~40 mA x 2...EDIT: The RiTdisplay datasheet indicates 480 mW power consumption for all pixels on at contrast 0x77, so 32 mA@3.3V. I doubt it's that low.