XS-L1-64LQFP data sheet clarification please

[mikronauts]

page 13 says:

"Ports 1A, 1C, 1D, 1H, 1I, 1J, 1K and 1L are nominal 8mA drivers, the remainder of the
general-purpose I/Os are 4 mA.

C Measured with 4mA drivers sourcing 4 mA, 8mA drivers sourcing 8 mA."

I took a look at the XC-5 schematics

the value of R12, R13, R16, R17 for the "button" LED's are not given, and they are on P4E

Based on the data sheet, P4E should not source/sink more than 4mA

The 330R resistor used for LED 1-12 also looks suspicious as assuming a normal Vdrop of 1.2V for the LED, the 330R resistors allow for 6mA from the port pins.

Are better electrical characterizations available?

[Bianco]

Typical vforward for green and red LEDs are higher than 1.2V.
(Starts around 1.6V for red and 1.9V for green, also depends on the materials used). Depending on the particular duoled used this can be within specs.

[mikronauts]

Thanks... unfortunately I have almost 60k low current LED's that the data sheet says have 1.2Vforward :)

I'll just use a 470R resistor, and limit them to 4mA - they light up starting around 2-3mA

Typical vforward for green and red LEDs are higher than 1.2V.
(Starts around 1.6V for red and 1.9V for green, also depends on the materials used). Depending on the particular duoled used this can be within specs.

[MaxFlashrom]

Thanks... unfortunately I have almost 60k low current LED's that the data sheet says have 1.2Vforward :)

I'll just use a 470R resistor, and limit them to 4mA - they light up starting around 2-3mA

Typical vforward for green and red LEDs are higher than 1.2V.
(Starts around 1.6V for red and 1.9V for green, also depends on the materials used). Depending on the particular duoled used this can be within specs.

I have just wired up a lot of different SMT 0603 Kingbright coloured LEDs to some output ports. They give a surprising amount of light even under 3mA. The datasheet says they are good to 20mA and the luminous intensity is pretty much proportionate to current. I'm not aiming to burn out my retinas, and it looks fine, on <=4mA. The Vf goes up with the current non-linearly, as the current increases, small increases in current lead to large increases in voltage drop, especially at lower currents, i.e. the LED resistance decreases, as the current increases(For a green LED, I'm looking at Vf= 1.95V @5ma i.e resistance of LED = 390Ohm; Vf = 2.1V @ 20mA, Resistance of LED = 105Ohm.) The voltage drop across the LED is current - dependent, making the choosing of an accompanying limiting resistor more difficult. You really need to choose a current, read off the graph for voltage and then do your sums. A trial and error method works fine too. At 3.3V, 470Ohm is a good start and should give under 3mA. Of course you can measure the voltage drop across your LED and also across its series resistor when it's on and confirm the current flowing. (I=V/R across series resistor gives current through LED, of course)

I imagine your LEDs are red- they tend to have the lowest Vf; Vf for blue/white LEDs are much higher(2.75V @4mA for the one I used. It looks a bit turquoise for my liking-I prefer the midnight/peacock blue look.

The blue LED I have shows that at 20mA, Vf = 3.3V and Imax is 20mA. What this means is that one can run this quite happily off 3.3V without a series resistor!

The issue is complicated by the fact that different LED colours give out different luminous intensities for the same current, and then of course there's the response of the human eye to consider. In practice this means trial and error within the current limits to make it look nice.

Max.

[mikronauts]

Thanks, good info.

I normally use 470R already :) however I think I'll run some experiments, and dig out the data sheets for my LED's... or simply measure the Vforward.

Thanks... unfortunately I have almost
60k low current LED's that the data sheet says have 1.2Vforward :)

I'll just use a 470R resistor, and limit them to 4mA - they light up starting around 2-3mA

Typical vforward for green and red LEDs are higher than 1.2V.
(Starts around 1.6V for red and 1.9V for green, also depends on the materials used). Depending on the particular duoled used this can be within specs.

I have just wired up a lot of different SMT 0603 Kingbright coloured LEDs to some output ports. They give a surprising amount of light even under 3mA. The datasheet says they are good to 20mA and the luminous intensity is pretty much proportionate to current. I'm not aiming to burn out my retinas, and it looks fine, on <=4mA. The Vf goes up with the current non-linearly, as the current increases, small increases in current lead to large increases in voltage drop, especially at lower currents, i.e. the LED resistance decreases, as the current increases(For a green LED, I'm looking at Vf= 1.95V @5ma i.e resistance of LED = 390Ohm; Vf = 2.1V @ 20mA, Resistance of LED = 105Ohm.) The voltage drop across the LED is current - dependent, making the choosing of an accompanying limiting resistor more difficult. You really need to choose a current, read off the graph for voltage and then do your sums. A trial and error method works fine too. At 3.3V, 470Ohm is a good start and should give under 3mA. Of course you can measure the voltage drop across your LED and also across its series resistor when it's on and confirm the current flowing. (I=V/R across series resistor gives current through LED, of course)

I imagine your LEDs are red- they tend to have the lowest Vf; Vf for blue/white LEDs are much higher(2.75V @4mA for the one I used. It looks a bit turquoise for my liking-I prefer the midnight/peacock blue look.

The blue LED I have shows that at 20mA, Vf = 3.3V and Imax is 20mA. What this means is that one can run this quite happily off 3.3V without a series resistor!

The issue is complicated by the fact that different LED colours give out different luminous intensities for the same current, and then of course there's the response of the human eye to consider. In practice this means trial and error within the current limits to make it look nice.

Max.