BH1680FVC
Technical Note
4/8
www.rohm.com
2012.02 - Rev.B
© 2012 ROHM Co., Ltd. All rights reserved.
●External parts Setting
1) Gain setting of BH1680FVC
Please select the best gain controlled by 3 and 4pin based on the required illuminance range.
The reference is as follows.
Illuminance detection range [lx] Gain Mode
~100 H-Gain Mode
~1,000 M-Gain Mode
~50,000 L-Gain Mode
This device will be mounted under the optical window in actual designing. Therefore, there is a possibility that the
illuminace to ALS( Ambient Light Sensor) will be less than the illuminance on the final product surface. Please consider the
attenuation of light through the optical window. Please set output resistance value( R1) within the range of 1 kΩ~1MΩ
which needs to be smaller than the input impedance of the next circuit.
2) Approximate formula of IOUT output voltage in each Gain Mode
(1) H-Gain mode
The output voltage is calculated as below.
Viout= 6.1 x 10
-6
x Ev x R1
Viout is IOUT output voltage [V]. Ev is an illuminance of the ALS surface [lx].
R1 is IOUT output resistor[Ω].
(For example) In case you want to convert the illuminance value up to 50 lx by ADC.
If the maximum voltage of ADC input is 2V, output resistor value will be as below.
R1 = Viout/(6.1 x 10
-6
x Ev)
= 2 /(6.1 x 10
-6
x 50) = 6557[Ω]
⇒6.8[kΩ]
(2) M-Gain mode
Viout= 0.61 x 10
-6
x Ev x R1
(3) L-Gain mode
Viout= 0.061 x 10
-6
x Ev x R1
3) C1
(1) To reject the flicker light.
In case IOUT output is R1 only and an ALS receives the artificial lights such as fluorescent lamps and incandescent
lamps synchronized with 50/60 Hz of AC power supplies, the output current has a ripple. If you want to reject this ripple,
please add C1 to R1 in parallel. Please set it to C1 x R1 = about 0.1 as a time constant.
(For example) If the R1 = 6.8[kΩ], C1 value will be as below.
C1 = 0.1 / R1
= 0.1 / ( 6.8 x 10
3
) = 14.7 x 10
-6
[F]
⇒15[uF]
(2) To control backlight smoothly by using illuminance value.
C1 is effective to control backlight smoothly for a rapid changing of the illuminance. In this case, please set it to
C1 x R1 = about 1 ~ 10 as a time constant. It is not necessary if you average illuminance value with software to change
backlight smoothly.
Please note that the rise time becomes slow at power-on and recovery from shutdown mode to operation mode.
