NOA1212CUTAG

NOA1212
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7
DESCRIPTION OF OPERATION
Ambient Light Sensor Architecture
The NOA1212 employs a sensitive photo diode fabricated
in ON Semiconductors standard CMOS process
technology. The major components of this sensor are as
shown in Figure 2 . The photons which are to be detected
pass through an ON Semiconductor proprietary color filter
limiting extraneous photons and thus performing as a band
pass filter on the incident wave front. The filter only
transmits photons in the visible spectrum which are
primarily detected by the human eye and exhibits excellent
IR rejection. The photo response of this sensor is as shown
in Figure 3.
The ambient light signal detected by the photo diode is
converted to an analog output current by an amplifier with
programmable gain. Table 4 shows the gain setting and the
corresponding light sensitivity.
Table 4. PROGRAMMABLE GAIN SETTINGS
GB2 GB1 Mode
Approximate Output
Current @ 100 lux
Approximate Output
Current @ 1000 lux
Saturation
0 0 Power Down
0 1 High Gain
51 mA 510 mA
~10,000 lux
1 0 Medium Gain
4.9 mA 49 mA
~100,000 lux
1 1 Low Gain
0.54 mA 5.4 mA
> 100,000 lux
Power Down Mode
This device can be placed in a power down mode by
setting GB1 and GB2 to logic low level.
In order for proper operation of this mode GB1 and GB2
should stay low 1.5 ms.
External Component Selection
The NOA1212 outputs a current in direct response to the
incident illumination. In many applications it is desirable to
convert the output current into voltage. It may also be
desirable to filter the effects of 50/60 Hz flicker or other light
source transients.
Conversion from current to voltage may be accomplished
by adding load resistor R
L
to the output. The value of R
L
is
bounded on the high side by the potential output saturation
of the amplifier at high ambient light levels. R
L
is bounded
on the low side by the output current limiting of the internal
amplifier and to minimize power consumption.
Equation 1 describes the relationship of light input to
current output for the High−Gain mode.
I
OUT
+
ǒ
51 mAń100 lux
Ǔ
*E
V
(eq. 1)
By adding R
L
to the output, I
OUT
is converted into a
voltage according to Equation 2.
V
OUT
+ I
OUT
*R
L
+
ǒ
51 mAń100 lux
Ǔ
*E
V
*R
L
(eq. 2)
The range of the output voltage is limited by the output
stage to the V
OMAX
parameter value of V
DD
– 0.4 V at the
maximum desired E
V
as shown in Equation 3. Equation 4
computes the value for R
L
(High−Gain mode).
V
OMAX
+
ǒ
51 mAń100 lux
Ǔ
*E
VMAX
*R
L
(eq. 3)
R
L
+
ǒ
V
DD
* 0.4 V
Ǔ
ńE
VMAX
*
ǒ
100 luxń51 mA
Ǔ
(eq. 4)
For example, consider a 5 V supply with a desired E
VMAX
= 1000 lux, the value of R
L
would be 8.85 kW. The value for
R
L
can easily be computed for different NOA1212 gain
ranges by substituting the appropriate output current at
100 lux from Table 4.
The optional capacitor C
L
can be used to form a low−pass
filter to remove 50/60 Hz filter or other unwanted noise
sources as computed with Equation 5.
C
L
+ 1ń2pf
c
R
L
(eq. 5)
For our example, to filter out 60Hz flicker the value of C
L
would be 300 nF.
Power Supply Bypassing and Printed Circuit Board
Design
Power supply bypass and decoupling can typically be
handled with a low cost 0.1 mF to 1.0 mF capacitor.
The exposed pad on the bottom of the package is internally
connected to VSS pin 2 and should be soldered to the printed
circuit board.
NOA1212
www.onsemi.com
8
PACKAGE DIMENSIONS
CUDFN6, 1.6x1.6, 0.5P
CASE 505AL
ISSUE O
NOTES:
1. DIMENSIONING AND TOLERANCING PER
ASME Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. DIMENSION b APPLIES TO PLATED
TERMINAL AND IS MEASURED BETWEEN
0.10 AND 0.20MM FROM THE TERMINAL TIP.
4. COPLANARITY APPLIES TO THE EXPOSED
PAD AS WELL AS THE TERMINALS.
A
D
E
B
C0.10
PIN 1
2X
2X
TOP VIEW
SIDE VIEW
BOTTOM VIEW
L
D2
E2
C
C0.10
C0.10
C0.08
A1
SEATING
PLANE
6X
NOTE 3
b
6X
0.10 C
0.05 C
A
BB
DIM MIN MAX
MILLIMETERS
A 0.55 0.65
A1 0.00 0.05
b 0.15 0.25
D 1.60 BSC
D2 1.05 1.15
E 1.60 BSC
E2 0.45 0.55
e 0.50 BSC
L 0.25 0.35
1
3
6
NOTE 4
PIN ONE
A3 0.20 REF
A3
A
e
b2 0.15 REF
4
b2
MOUNTING FOOTPRINT*
DIMENSIONS: MILLIMETERS
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
6X
0.48
0.50
PITCH
1.70
1.90
6X
0.28
0.75
1
RECOMMENDED
L2 0.17 REF
REFERENCE
L2
A
M
0.10 BC
A
M
0.10 BC
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NOA1213/D
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NOA1212CUTAG

Mfr. #:
Manufacturer:
ON Semiconductor
Description:
Optical Sensors Ambient Light Sensors ANALOG ALS HIGH GAIN
Lifecycle:
New from this manufacturer.
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