TSL2550 View Datasheet(PDF) - Unspecified

Part Name

Description

Manufacturer

TSL2550

AMBIENT LIGHT SENSOR WITH SMBus INTERFACE

Unspecified 

PRINCIPLES OF OPERATION

TSL2550

AMBIENT LIGHT SENSOR

WITH SMBus INTERFACE

TAOS029 – SEPTEMBER 2002

Analog-to-Digital Converter

The TSL2550 contains an integrating analog-to-digital converter (ADC) that integrates a photodiode current.

First it integrates channel 0 photodiode current and then it integrates channel 1 photodiode current. At the end

of the conversion cycle for each channel (approximately 400 ms), the conversion result is transferred to the

appropriate channel 0 or channel 1 ADC register. The transfer is double-buffered to ensure that invalid data is

not read during the transfer. After the data is transferred, the TSL2550 automatically begins the next conversion

cycle. Approximately 800 ms is required for both Channel 0 and Channel 1 ADC registers to be updated. A

VALID bit is used to indicate that data has been written to the ADC register after ADC is enabled.

Interface to the ADC and control of other device functions is accomplished using the standard 2-wire System

Management Bus (SMBus) interface. Both versions 1.1 and 2.0 of the SMBus are supported.

Digital Interface

The TSL2550 contains an 8-bit command register that can be written and read via the SMBus. The command

register controls the overall operation of the device. There are two read-only registers that contain the latest

converted value of each of the two ADC channels. The SMBus slave address is hardwired internally as 0111001

(MSB to LSB, A6 to A0).

Both the send byte protocol and the receive byte protocol are implemented in the TSL2550. The send byte

protocol allows single bytes of data to be written to the device (see Figure 6). The written byte is called the

COMMAND byte. The receive byte protocol allows single bytes of data to be read from the device (see Figure

7). The receive data can be either the previously written COMMAND byte or the data from one of the ADC

channels.

1

7

S Slave Address

11

WR A

8

Data Byte

11

AP

S = Start Condition

P = Stop Condition

Shaded = Slave Transmission

Figure 6. Send Byte Protocol

1

7

S Slave Address

11

RD A

8

Data Byte

11

AP

S = Start Condition

P = Stop Condition

Shaded = Slave Transmission

Figure 7. Receive Byte Protocol

The LUMENOLOGYr Company

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Copyright E 2002, TAOS Inc.

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