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I
LED
(mA) +
ƪ
ǒ
1.254
R
IS
) 1.276 10
*6
Ǔ
Step 500
3.5 10
*6
ƫ
*
ǒ
1.254
R
IS
) 1.276 10
*6
Ǔ
1714.29 10
6
(1)
I
LED
(mA) +
ǒ
1.254
R
IS
) 1.276 10
*6
Ǔ
Step 100
3.5 10
*6
(2)
TPS60251
SLVS767C – APRIL 2007 – REVISED NOVEMBER 2007
Where R
IS
is the resistor from IS to GND, I
LED
is the LED current in µ A and Step is the dimming step set by the
I
2
C interface (1 to 63). I
LED
may be set up to 25mA (R
IS
= 562 k Ω ).
R
IS
has an effect on the current steps that are programmed using the I
2
C. When the current is programmed
below 1.5mA, the current is determined by the following equation:
This equation provides a greater resolution in current steps at lower currents.
STEP ILED STEP ILED STEP ILED STEP ILED
1 100 µ A 17 2.5mA 33 10.5mA 49 18.5mA
2 200 µ A 18 3.0mA 34 11.0mA 50 19.0mA
3 300 µ A 19 3.5mA 35 11.5mA 51 19.5mA
4 400 µ A 20 4.0mA 36 12.0mA 52 20.0mA
5 500 µ A 21 4.5mA 37 12.5mA 53 20.5mA
6 600 µ A 22 5.0mA 38 13.0mA 54 21.0mA
7 700 µ A 23 5.5mA 39 13.5mA 55 21.5mA
8 800 µ A 24 6.0mA 40 14.0mA 56 22.0mA
9 900 µ A 25 6.5mA 41 14.5mA 57 22.5mA
10 1.0mA 26 7.0mA 42 15.0mA 58 23.0mA
11 1.1mA 27 7.5mA 43 15.5mA 59 23.5mA
12 1.2mA 28 8.0mA 44 16.0mA 60 24.0mA
13 1.3mA 29 8.5mA 45 16.5mA 61 24.5mA
14 1.4mA 30 9.0mA 46 17.0mA 62 25.0mA
15 1.5mA 31 9.5mA 47 17.5mA 63 25.5mA
16 2.0mA 32 10.0mA 48 18.0mA
Figure 14. Dimming Steps for Sub, Main, and Keypad Backlight
Figure 14 shows the dimming steps for sub, main, and auxiliary display banks in the 25mA maximum current
application. To satisfy today ’ s requirements on LED current, the TPS60251 covers low LED current area from
100 µ A to 1.5mA with 100- µ A dimming step (total 16 steps for 25-mA maximum current) for the new LCD panels
which have improved transparency rates. For LED currents in the range from 2mA to 25mA, the device uses 48
dimming steps with 0.5mA step. Also, DM5 has 4 dimming steps once the current path is assigned for auxiliary
applications with maximum 80-mA current.
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Product Folder Link(s): TPS60251