TSL4531
DIGITAL AMBIENT LIGHT SENSOR
TAOS112 − OCTOBER 2011
6
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Copyright E 2011, TAOS Inc.
The LUMENOLOGY r Company
www.taosinc.com
PRINCIPLES OF OPERATION
Analog-to-Digital Converter
The TSL4531 contains one integrating analog-to-digital converter (ADC) that integrates the current from the
photodiode array. Upon completion of the conversion cycle, the conversion result is transferred to the data
registers. Transfers are double-buffered to ensure that invalid data is not read during the transfer. After the
transfer, the device will either automatically begin another integration cycle, or enter power-down mode,
depending upon the mode setting in the control register.
The device features several key power management features. The mode of operation can be controlled to
provide either continuous operation or single acquisition operation followed by a power-down state. In the
continuous operation, a secondary mode can be enabled allowing the device to go into a low-power state in
between each acquisition cycle.
The device allows the user to control the integration time. This enables the user to control the sensitivity of the
device to allow for the greater dynamic range needed in bright lighting conditions such as sunlight. Integration
times of 400 ms, 200 ms, or 100 ms are available. All integration times are multiples of 50 ms, allowing rejection
of 50/60-Hz ripple present in a typical fluorescent lights. The lux output needs to be scaled depending on the
integration time as shown in the calculating lux section.
Calculating Lux
The ADC output is a 16-bit number that is directly proportional to the value that approximates the human eye
response in the commonly used illuminance unit of lux. The light level can be calculated using the following
expression.
Light Level (lux) = MULTIPLIER × [ (DATAHIGH << 8) + DATALOW ]
Where: MULTIPLIER = 1 for TCNTRL = 00 (Tint = 400 ms),
MULTIPLIER = 2 for TCNTRL = 01 (Tint = 200 ms), and
MULTIPLIER = 4 for TCNTRL = 10 (Tint = 100 ms), and
<< 8 indicates a logical 8-bit shift left operation, and
TCNTRL is a 2-bit field in the configuration register (0x01)
Example:
MULTIPLIER = 1
DATALOW = 0x9C
DATAHIGH = 0x63
Illuminance = 1 × [ (DATAHIGH << 8) + DATALOW] lux
= (0x63 << 8) + 0x9C lux
= 0x639C lux
= 25,500 lux
