ADPD107 Drive current settings not matching datasheet formula

Hi FormerMember,

We are seeing what looks like inaccuracies in the drive current on the ADPD107. The datasheet says the drive current should be:

LEDPeak = (50.3 + 19.8 * ILED_COARSE) * (0.74 + 0.022 * ILED_FINE) * (0.4 + 0.6 * ILED_SCALE)

We are trying to use these settings create a range of LED drive currents, and we are seeing this behavior:

You can see that the measured response (on a constant material), has some point where an increase would be expected but a decrease occurs. These point also appear to align with changes in the 'scale' setting. Note that the scale variable is multiplied by 10 to make it easier to see in the plot.

Is the equation in the datasheet accurate? I am also attaching a table of the data (PD is response, drive_i is expected drive current):

PD coarse drive_i fine scale
935.440677966 0 16.65936 4 0
1057.40229885 0 18.42992 8 0
1118.95454545 0 19.3152 10 0
1181.18823529 0 20.20048 12 0
1241.93023256 0 21.08576 14 0
1426.37647059 1 21.98336 2 0
1387.70114943 0 23.29896 19 0
1614.46987952 1 24.45088 6 0
1701.94047619 1 25.68464 8 0
1794.60465116 1 26.9184 10 0
1936.65116279 2 28.19264 2 0
2058.68965517 2 29.77488 4 0
2100.72619048 1 31.23656 17 0
2291.37647059 2 32.93936 8 0
2419.96470588 3 34.40192 2 0
2523.6741573 2 36.10384 12 0
2566.27380952 1 38.02224 28 0
2690.70786517 1 39.87288 31 0
2964.93975904 4 41.7508 3 0
2169.70114943 0 43.8616 6 1
2306.63855422 0 46.0748 8 1
2448.85416667 0 48.288 10 1
3566.15853659 3 50.81304 19 0
3765.92941176 5 53.38968 7 0
3916.85227273 6 56.00592 4 0
4091.47727273 4 58.8448 18 0
4226.15853659 8 61.7752 0 0
3416.71764706 0 64.887 25 1
4597.01190476 4 67.9616 26 0
3769.11494253 0 71.5266 31 1
4301.30681818 1 75.007 15 1
5148.85365854 7 79.18688 14 0
4650.88235294 1 82.718 20 1
5403.25581395 10 86.60704 6 0
5572.18823529 8 91.16016 16 0
5706.42528736 9 95.7872 14 0
5811.93975904 11 100.59112 9 0
5891.54117647 14 105.586 3 0
6028.63636364 10 110.64248 17 0
6132.56321839 8 116.872 30 0
5825.17647059 3 122.2058 17 1
6255.38372093 12 128.28824 17 0
6314.61111111 10 134.67792 28 0
5995.1547619 3 141.513 25 1
6385.36170213 12 148.5564 25 0
6046.01204819 3 155.9934 31 1
6416.24242424 12 163.75752 31 0
drive_i_vs_res.csv.zip
  • +1
    •  Analog Employees 
    on Dec 8, 2017 4:31 PM

    Hello,

    The equation in the datasheet for LED drive current should be accurate to ~10%, however, it is true that the transfer function is not monotonic as you step through the coarse and fine settings. So when stepping from one coarse setting with a high fine setting to the next highest coarse setting at a low fine setting you may actually see the current drop due to this non-monotonicity.

    Regards,

    Kevin