Newhaven Products > Evaluation Tools

NHD-TFT40 PWM pin

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Paul_B:
Morning,

The NHD-TFT40 is designed to work with our 24-bit Parallel RGB Interface TFT displays that require the RGB pixel data to be clocked in continuously.

The backlight driver defaults to 40mA and can boost up to ~24VDC for up to 7-LED strings. Check your display datasheet for the string configuration.

Per your request I pulled the NHD-TFT40 from stock and connected it to the NHD-4.3-480272EF-ATXL#.

Please see the attached images, note that when the PWM signal is tied to GND the backlight turns off as expected.







dttworld:
Thanks for running the test on your end.

I am using the eval board for just the backlight function set to 90mA.

 I should be receiving my parts from Mouser on Wednesday and will provide an update after I do some testing.

dttworld:
So I swapped out the backlight IC with one bought from Mouser. Unfortunately, the PWM pin tied to gnd still doesn't turn off the backlight current. For this test I am actually lighting up 5 LEDs in parallel with the demo board. This really doesn't make sense to me.

Could you run a test where you light up 5 parallel LEDs and see if tying PWM to gnd turns the LEDs off?

Thank you

dttworld:
I believe I understand my problem now. The backlight converter on the eval board is a boost converter designed to drive a series LED backlight. I actually need a buck converter designed to drive the parallel LED backlight found on the HD-1.8-128160EF-CSXN-F.

Spletonna:
Ah, I appreciate you commenting back on fixing your issue. It's helped me learn a few things myself.

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