Backlight Power Measurement

[Werner Almesberger]

Joerg Reisenweber wrote:
> Nope it won't, as the converter is powering the LED plus R.

Argh, of course. I got that the wrong way around :-(

Now something funny: I tried the same setup with a GTA02v4, and I found
that it capped Vledfb at only 60 mV:

LEDOUT  Vbat    Ibat    Pbat    Vledout Vledfb  (V)     Isense  Vled    Pled   
        (V)     (mA)    (mW)    (V)     nominal meas.   (mA)    (V)     (mW)   
0x01      4.195     149 625.054  10.539   0.003   0.004   0.100  10.534   1.056
0x02      4.194     153 641.753  10.806   0.006   0.008   0.191  10.798   2.057
0x03      4.194     160 670.990  11.097   0.009   0.014   0.326  11.083   3.616
0x04      4.194     164 687.765  11.241   0.012   0.017   0.402  11.224   4.510
0x05      4.193     166 696.007  11.332   0.016   0.019   0.452  11.313   5.112
0x06      4.192     176 737.854  11.615   0.020   0.026   0.619  11.589   7.177
0x07      4.192     183 767.080  11.856   0.023   0.033   0.773  11.824   9.141
0x08      4.192     187 783.887  11.959   0.028   0.036   0.842  11.923  10.033
0x09      4.191     196 821.494  12.177   0.032   0.042   0.990  12.135  12.012
0x0a      4.190     204 854.823  12.375   0.036   0.048   1.130  12.328  13.930
0x0b      4.190     214 896.604  12.577   0.041   0.054   1.277  12.523  15.994
0x0c      4.189     222 929.948  12.754   0.046   0.060   1.410  12.695  17.903
0x0d      4.189     222 929.966  12.754   0.051   0.060   1.414  12.694  17.948
0x0e      4.189     222 930.000  12.753   0.057   0.060   1.414  12.693  17.951
0x0f      4.189     224 938.342  12.752   0.063   0.060   1.414  12.692  17.945
[...]

Note sure what happened to the poor device.

- Werner