TSL2550T TAOS, TSL2550T Datasheet - Page 9

• Manufacturer Part Number: TSL2550T
• Description: Industrial Optical Sensors Ambient Light Sensor SMBus
• Manufacturer: TAOS
• Type: Ambient Light Sensor with Digital Outputr

Specifications of TSL2550T

• Product: Ambient Light Sensor
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

NOTES: A. CHORD VALUE = INT (16.5
The LUMENOLOGY r Company
The specific ADC value register read depends on the last read command written to the command register, as
described above and in the Operation section, below.
The MSB of the ADC register (VALID bit B7) is used to indicate that data has been written to the ADC register
after the device is powered up as described in Command Register section.
Bits 6 through 0 contain the 7-bit code representing the ADC count value, which is proportional to a
photodetector current. In this code, the ADC count value is represented by a piece-wise linear approximation
to a log function. The transfer function is broken into 8 chords of 16 steps each. (This code is very similar to μ-law
code used in audio compression — it differs in that it does not have a sign bit and it is not inverted.) Table 3 shows
the relationship between the CHORD and STEP bits and the CHORD and STEP numbers and values. These
are used to calculate the ADC count value.
The ADC count value is obtained by adding the CHORD VALUE and the product of the STEP NUMBER and
STEP VALUE (which depends on CHORD NUMBER).
The ADC count value can also be expressed as a formula:
where:
B. STEP VALUE = 2
B6, B5, B4
CHORD
BITS
000
001
010
011
100
101
110
111
ADC Count Value + (INT (16.5
ADC Count Value + ((Chord Value) ) (Step Value)
Table 3. CHORD and STEP Numbers and Values vs Register Bits
C, CHORD
C
S
as defined in Table 3.
NUMBER
C
0
1
2
3
4
5
6
7
is the CHORD NUMBER (0 to 7)
is the STEP NUMBER (0 to 15)
×
((2
(Note A)
CHORD
VALUE
C
1039
2095
115
247
511
) − 1))
16
49
0
r
www.taosinc.com
(Note B)
VALUE
STEP
128
16
32
64
1
2
4
8
((2
C
* 1))) ) (S
(2
r
(Step Number))
B3, B2, B1, B0
C
))
STEP
AMBIENT LIGHT SENSOR
BITS
0000
0001
0010
0100
0101
1000
1001
1010
0011
0110
0111
1011
1100
1101
1110
1111
WITH SMBus INTERFACE
TAOS029L − OCTOBER 2007
NUMBER
S, STEP
Copyright E 2007, TAOS Inc.
10
11
12
13
14
15
0
1
2
3
4
5
6
7
8
9
TSL2550
9