Industry’s Lowest-Power
Ambient Light Sensor with ADC
The count is multiplied by 0.045, which is the LSB.
Because of the logarithmic nature of autoranging cir-
cuitry implemented on the IC, resolution of ambient lux
readings scale with the absolute measurement. Table 8
lists the lux resolution and the lux ranges obtained from
the IC.
Interrupt Settings
Interrupt is enabled by setting bit 0 of register 0x01 to
1 (see Table 1). INT , an open-drain output, pulls low
when an interrupt condition occurs (lux readings that
exceed threshold limits for a period greater than that set
by the Time register). The interrupt status bit is cleared
automatically if register 0x00 is read or if the interrupt is
disabled (INTE = 0).
Threshold Register Data Format
The IC’s interrupt circuit requires the upper and lower
limit thresholds to be in a specific format to be properly
interpreted. The upper and lower limits, from registers
0x05 and 0x06 must match the lux high-byte format. This
consists of the 4 bits of the exponent and the 4 most sig-
nificant bits of the mantissa (E3 E2 E1 E0 M7 M6 M5 M4).
In this case, there is the following formula:
Lower lux threshold = (2 (exponent) x mantissa) x 0.045
The exponent is a 4-bit number ranging from 0000 to
1110 (zero to 14).
Table 8. Lux per LSB in Automatic Mode
The mantissa is an 8-bit number ranging from 0000 0000
to 1111 0000 (zero to 240).
Upper lux threshold = (2 (exponent) x mantissa) x 0.045
The exponent is a 4-bit number ranging from 0000 to
1110 (zero to 14).
The mantissa is an 8-bit number ranging from 0000 1111
to 1111 1111 (15 to 255).
In the auto range mode (MANUAL = 0), the upper thresh-
old and lower threshold bytes must be in a format that
matches the format used in register 0x03, the lux high
byte. There are only two rules to follow:
?  For  very  low  lux  levels  (light  levels  below  11.5  lux), 
set the exponent to zero, the code is merely: 0000
MMMM where the 4 zeroes are the exponent, and the
MMMM represent the 4 most significant bits of the
mantissa.
?  For  all  other  conditions  (light  levels  above  11.5  lux) 
where the exponent is not zero, the format is: EEEE
1MMM. Notice that bit M7 (most significant bit) must
always be a 1. The other bits do not matter. EEEE is
limited to a maximum value of 1110. The maximum
usable setting is a code of 1110 1111.
In manual mode (MANUAL = 1), Table 9 gives the range
of exponent (E3 E2 E1 E0) that can be used for each
TIM[2:0] and CDR bit setting.
LUX (MIN)
0
11.5
23.0
46.1
92.2
184.3
368.6
737.3
1474.6
2949.1
5898.2
11,796.5
23,593.0
47,185.9
94,371.8
LUX (MAX)
11.5
23.0
46.1
92.2
184.3
368.6
737.3
1474.6
2949.1
5898.2
11,796.5
23,593.0
47,185.9
94,371.8
188,006.4
LUX PER LSB IN
AUTOMATIC MODE
0.045
0.09
0.18
0.36
0.72
1.44
2.88
5.76
11.52
23.04
46.08
92.16
184.32
368.64
737.28
COUNTS (MIN)
0
256
512
1024
2048
4096
8192
16,384
32,768
65,536
131,072
262,144
524,288
1,048,576
2,097,152
COUNTS (MAX)
256
512
1024
2048
4096
8192
16,384
32,768
65,536
131,072
262,144
524,288
1,048,576
2,097,152
4,177,920
12
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