ncp5890 ON Semiconductor, ncp5890 Datasheet - Page 13

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

Ambient Light Control
diode, to automatically adjust the I−LED peak current as a
function of the ambient light. A dedicated I2C command is
used to activate or de−activate this function. On the other
hand, the end user shall set up the maximum I−LED current
by means of an I2C command. The photo sense is
automatically de−activated when an I2C command is send
through the port, and resume to the pre−programmed status
when the I2C command is completed.
current and the photo sense feedback, associated to a
Up/Down counter to properly setup the contrast at display
level. The photo sense action is bounded by two limits:
ically adjust the gain of the photo current. Such capability is carried out by the internal register loaded through the I2C port.
PHGAIN[0..7]
Bit [B7] : Photo sense VSD bias control
Bit [B7] :
Bit [B7] :
Bits [B6:B5] : RFU
Bits [B4:B0] : Photo sensor gain adjust
digitally combined to get different gain in the range 0 to 7.5: example below
The ambient light can be monitored, by an extra photo
The concept is based on analog monitoring of the I−LED
Since several types of photo sensor can be used in the final application, provisions have been taken into account to dynam−
The photo sensor no longer influences the I−LED when the gain is setup to $00. On the other hand, the five bits can be
RESET
Gain
VSD
B7
1
1
1
B7 = 0 ³ VSD disconnected, photo sense function de−activated
B7 = 1 ³ VSD connected, photo sense function activated
SFH5711
VSD
B7
B6
Log
0
0
0
0
0
U3
1
GND
2
4
R1 22k
B6
B5
0
0
0
0
0
0
GND
220k
R2
Figure 12. Basic Photo Sense Input Circuit
C1
PHG5
2.2uF
AMBS
B5
B4
VSB
0
0
0
0
1
4
5
http://onsemi.com
I2C
PHG5
PHG4
R
B4
B3
13
0
4
0
0
0
+VBat
− upper I−LED as defined by the end user: the photo
− lower I−LED as defined by the end user: the photo
direction), a selectable low frequency clock drives the
counter, yielding a smooth and slow brightness variation.
tubes, is filter out by means of an external network built
between the photo sensor and the AMBS pin. Generally
speaking, such a filter is built with a RC network designed
to cope with the electrical performances of the selected
photo sense. As a consequence, the AMBS pin is biased by
a low level voltage signal and processed accordingly the
ambient light control structure: see Figure 15.
When the photo sense activates the counter (in either
The 100 Hz noise, coming from standard fluorescent
R/4
sense cannot increase the I−LED above such a limit
sense cannot reduce the back light current to zero.
R/2
R/2
2R
4R
R
PHG4
PHG3
B3
B2
0
2
0
1
1
U1
R
GND
PHG3
PHG2
B2
B1
0
1
0
0
0
MONITORING
GAIN
VSB
ANALOG
PHG2
PHG1
0.50
0.25
B1
B0
0
0
0
PHG1
Gain
0.25
1.25
B0
0
0
5