ncp5890 ON Semiconductor, ncp5890 Datasheet - Page 14

• Manufacturer Part Number: ncp5890
• Description: Light Management Ic Dedicated For Lcd Backlighting And Multi-led Fun Light Applications
• Manufacturer: ON Semiconductor

in comparison to the maximum level set up by the user, the
I−LED decreases with a timing defined by an I2C
PHCLK[0..7]
Bits [B7] : RFU
Bits [B6] : RFU
Bits[B5:B0] :
Bits [B7] : RFU
transition of the backlight from maximum toward the minimum calculated by the photo sense, the timing of the negative
going slope is twice the timing of the positive going slope.
programmable (according to the PHTIM register contain).
The timing is defined by the PHTIM[B4:B0] bits
multiplied by the number of steps necessary to reduce /
increase the I−LED form one value to the next limit.
PHMIM[0..7]
Bits [B7:B4] : RFU
Bits[B3:B0] : set up the I−LED minimum value, according to the logarithmic table.
When the photo sense returns a lower ambient light level
PHT1 = Photo sense clock = 20 Hz ³ T = 50 ms/step
PHT2 = Photo sense clock = 10 Hz ³ T = 100 ms/step
PHT3 = Photo sense clock = 5 Hz ³ T = 200 ms/step
PHT4 = Photo sense clock = 2.5 Hz ³ T = 400 ms/step
PHT5 = Photo sense clock = 1.25 Hz ³ T = 800 ms/step
PHT6 = Photo sense clock = 0.6 MHz ³ T = 1600 ms/step
Note: the bits cannot be combined to generate a different timing.
In addition, the positive and negative slopes of the I-LED current are intentionally different. In order to generate a smooth
The rise and fall time of the I−LED current are
RESET
RESET
Phot Sense AMBS
B7
B7
0
0
0
0
I−LED maximum
I−LED minimum
B6
B6
0
0
0
0
Figure 13. Basic Photo Sense Timing
16ms to 7500ms
PHT6
B5
B5
0
0
0
PHTIM
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PHT5
B4
B4
14
0
0
0
command. Such a timing is derived from the Low
Frequency clock and selected by the PHTIM register (see
Figure 13).
during the Photo sense operation: the contain of the
PHMIN[B2:B0] register limits the low end current when
the photo sensor is in a dark environment.
On the other hand, the I−LED cannot be reduce to zero
16ms to 7500ms
PHM4
PHT4
B3
PHTIM
B3
0
0
PHM3
PHT3
B2
B2
0
0
PHM2
PHT2
B1
B1
0
0
PHM1
PHT1
B0
B0
0
0