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RA8875 Driver Board TFT Backlight Current Limits
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RA8875 Driver Board TFT Backlight Current Limits

by trawlergeek on Wed May 03, 2017 6:00 pm

Greetings:
I have mated the RA8875 driver board (ID: 1590) with the Adafruit 7" TFT LCD w/Touch (ID:2354). The TFT display works well with the exception of the back-light brightness. I discovered that the current default for the backlight drive defaults to 25 mA.
The 7" TFT display specifications (data sheet) mention backlight nominal current as 120 mA with 180 mA MAX.
When using 125 mA drive setup, the backlight brightness is very useful. But the power components are pretty warm. I need the IR temp gun from work to get real values.

Based on the circuit board and schematic (from the Eagle files), the RA8875 board has the ability (via solder program pads) to drive 25 mA (no jumper), 50 mA (+25), 125 mA (+100), and 150 mA (both +25 and +100 jumpers).

The product description for the RA8875 board only mentions the 25 mA and 50 mA options. It omits mentioning the +100 mA jumper function.

Will the board's 24 VDC boost regulator support the 125 mA and 150 mA current drive settings without excessive heating?

Are there any known issues that would prevent using the 125 mA setting and, therefore, that explains why there is no mention of those high current settings on the product page?

Great products, BTW. I really enjoy the boards and am looking to convert the sumotoy library to the Feather M0 and similar ARMs. (RA8875 library from https://github.com/sumotoy/RA8875)

Best regards and thanks in advance for your valuable time...

Jim

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Re: RA8875 Driver Board TFT Backlight Current Limits

by adafruit_support_rick on Wed May 03, 2017 7:19 pm

You can solder both jumpers closed. The booster will handle it just fine.

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Re: RA8875 Driver Board TFT Backlight Current Limits

by trawlergeek on Wed May 03, 2017 8:31 pm

Rick,
Awesome outcome. Thanks for the rapid reply...

Cheers
Jim

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Posts: 10
Joined: Sun Oct 07, 2012 7:15 pm

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