For a motorcycle dashboard project, I purchased this 5 inch sunlight readable screen, because I need the screen to be sunlight readable! https://www.newhavendisplay.com/specs/N ... F-ASXN.pdf
I plugged the screen in to the TFP401 decoder and the screen displayed the images with no problems. As expected however, the screen was a bit dim.
The data sheet for the display suggests a backlight current of between 60 and 75 mA. I tried using the +25 mA jumper, and I was barely able to notice the difference. I then used the +100 mA jumper and although the screen was much brighter, the screen switches off then back on again after a few seconds (and I'm probably killing the backlight).
I measured the voltage between pin 2 of the 40 pin FPC connector and I got around 25V for all three scenarios.
I was wondering whether by adding another resistor in the +100 mA jumper pad, I can get a current between 60 and 75mA?
With my limited physics knowledge and the assumption that the jumper pad is in series with the 3 ohm resistor associated with it, I've worked out that I would need between a 3 and 5.5 ohm resistor in the jumper (lower resistance = more current). Is there anything else I missed out?
TFP401 HDMI Decoder - 75mA Backlight
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- adafruit_support_mike
- Posts: 67485
- Joined: Thu Feb 11, 2010 2:51 pm
Re: TFP401 HDMI Decoder - 75mA Backlight
The FAN5333B LED driver tries to maintain 315mV across the sense resistor. The TFP401 breakout has a 12-Ohm resistor connected across that voltage by default, for a base current of 25mA.
To get 75mA you'd need a sense resistance of 4.2-Ohms.
You can get close to that by putting a 6.8-Ohm resistor in parallel with the existing 12-Ohm one. The parallel resistance will be 4.34-Ohms, which should give you about 72.6mA.
To get 75mA you'd need a sense resistance of 4.2-Ohms.
You can get close to that by putting a 6.8-Ohm resistor in parallel with the existing 12-Ohm one. The parallel resistance will be 4.34-Ohms, which should give you about 72.6mA.
- markos_rs
- Posts: 2
- Joined: Wed May 26, 2021 11:23 am
Re: TFP401 HDMI Decoder - 75mA Backlight
Thank you for your help,
By that did you mean that I can replace one of the resistors (eg the 12 ohm one associated with the +25mA jumper) and use the jumper pad?
If so, do you know which size resistors I would need please? Is it 0603?
By that did you mean that I can replace one of the resistors (eg the 12 ohm one associated with the +25mA jumper) and use the jumper pad?
If so, do you know which size resistors I would need please? Is it 0603?
- adafruit_support_mike
- Posts: 67485
- Joined: Thu Feb 11, 2010 2:51 pm
Re: TFP401 HDMI Decoder - 75mA Backlight
Yeah, replacing one of the existing resistors would work.
To pull an existing resistor off a board, get a piece of solid copper wire (24-gauge phone wire works well) and bend a U into the end. Each side of the U should touch one of the resistor's solder joints. Get a small blob of solder on the tip of your iron and touch it to the bend in the wire between the two solder joints. The solder will provide good heat transfer to the wire, and the wire will carry heat to both joints at the same time. When both joints melt, you can slide the resistor off its pads.
Clean any remaining solder off the pads with solder wick, and you're ready to place a new resistor.
Start by melting a small blob of solder onto one pad. That way you don't have to juggle the resistor, the iron, and the solder at the same time. Just hold the resistor to the tinned pad with one hand, heat the blob with the iron in your other hand, and the joint will form automatically. Then you can make the joint at the other end.
They're 0805s, which are easier to work with than it seems at first glance.markos_rs wrote:If so, do you know which size resistors I would need please? Is it 0603?
To pull an existing resistor off a board, get a piece of solid copper wire (24-gauge phone wire works well) and bend a U into the end. Each side of the U should touch one of the resistor's solder joints. Get a small blob of solder on the tip of your iron and touch it to the bend in the wire between the two solder joints. The solder will provide good heat transfer to the wire, and the wire will carry heat to both joints at the same time. When both joints melt, you can slide the resistor off its pads.
Clean any remaining solder off the pads with solder wick, and you're ready to place a new resistor.
Start by melting a small blob of solder onto one pad. That way you don't have to juggle the resistor, the iron, and the solder at the same time. Just hold the resistor to the tinned pad with one hand, heat the blob with the iron in your other hand, and the joint will form automatically. Then you can make the joint at the other end.
Please be positive and constructive with your questions and comments.