AMIS-749803 Datasheet, PDF (8/15 Pages) AMI SEMICONDUCTOR – (I2C) Ambient Light Sensor

AMIS–749803: (I²C) Ambient Light Sensor
Data Sheet
The ambient light signal that is detected by the photo diode is converted to digital signal using a variable slope integrating ADC. The
ADC that is used in this device has a maximum resolution of 16-bits unsigned value. The 16-bit ADC value is then provided to the
control block which is also connected to the I²C interface block.
The following equation (eq-1) shows the relationship of output counts C_nt as a function of integration constant I_k, integration time T_i (in
sec), and the intensity of the ambient light, I_L(in lux):
I_L = C_nt / (I_k * T_i)
Equation 1
where I_k = 3.3357
Hence the intensity of the ambient light, I_L(in lux):
I_L = C_nt / (3.3357 * T_i)
Equation 2
For example let:
C_nt = 1001
T_i = 300mS
Intensity of the ambient light, I_L(in lux):
I_L = 1001 / (3.3357 * 300mS)
I_L = 1000lux
8.0 I²C Interface
Equation 3
This device is capable of working as an I²C bus slave. Address of this device on I²C bus is always 0x39 (hexadecimal number 39).
Registers of this device can be programmed by sending commands over I²C bus. Ambient light intensity count value can be obtained
by reading registers of this device. Ambient light intensity count is a sixteen bits wide number and hence two I²C read operations are
needed. This device supports both the standard mode (100 Kbit/s) and the fast mode (400 Kbit/s) of I²C. Figure 11 shows an I²C write
operation. To write to an internal register of this device a command must be sent by an I²C master. As shown in Figure 11, the I²C write
command begins with a start condition. After the start condition, seven bits of address are sent MSB first. RD/WR_ command bit follows
the address bits. Upon receiving a valid address the device responds by driving I2CDATA low for an ACK. After receiving an ACK, I²C
master sends eight bits of data with MSB first. Upon receiving eight bits of data the device generates an ACK. I²C master terminates
this write command with a stop condition.
Figure 11: I²C Write Command
AMI Semiconductor – July 2006, M-20599-001
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