Technical Note
15/20
BH1730FVC
www.rohm.com
2012.02 - Rev.A
© 2012 ROHM Co., Ltd. All rights reserved.
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ALS sensitivity adjustment function
BH1730FVC is possible to change ALS sensitivity. And it is possible to cancel the optical window influence (difference with /
without optical window ) by using this function. Adjustment is done by changing measurement time. For example, when
transmission rate of optical window is 50% (measurement result becomes 0.5 times if optical window is set), influence of
optical window is ignored by changing sensor sensitivity from default to 2 times.
Sensitivity can be adjusted by ITIME (01h<7:0>). The measurement time is proportional to “256- ITIME”. For example,
sensitivity is twice when “256- ITIME” is twice, and the measurement time is twice, too.
The range of adjusting TIMING is below.
Min.
Typ.
Max.
Sensitivity
Default*0.026
Default
Default*6.711
range of TIMING (binary)
1111_1111
1101_1010
0000_0001
range of TIMING (decimal)
255
218
1
Measurement time
2.7ms
102.6ms
688.5ms
It is possible to detect 0.001 lx by using this function at GAIN = x128.
The below formula is to calculate illuminant per 1 count.
Illuminant per 1 count in Type0 at GAIN = x1( lx / count ) = 1 / 1.2 * (256 - 218) / (256 – X)
218 : Default value of ITIME (decimal)
X : ITIME value (decimal)
Illuminant per 1 count in Type0 at GAIN = x128( lx / count ) = 1 / 1.2 * (256 - 218) / (256 – X) / 128
218 : Default value of ITIME (decimal)
X : ITIME value (decimal)
128 : Gain value
Illuminant per 1 count in Type0 at GAIN = x1 is as following within adjustable range of ITIME.
ITIME value
Illuminant per 1count(lx / count)
1111_1111 31.67
1101_1010 0.833
0000_0001 0.124
Illuminant per 1 count in Type0 at GAIN = x128 is as following within adjustable range of ITIME.
ITIME value
Illuminant per 1count(lx / count)
1111_1111 0.247
1101_1010 0.007
0000_0001 0.001
Please take care that about 100,000lx or more cannot be measured even if decreasing the sensitivity.
