NOA1305

http://onsemi.com

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DESCRIPTION OF OPERATION

Ambient Light Sensor Architecture

The NOA1305 employs a sensitive photo diode fabricated

in ON Semiconductor’s standard CMOS process

technology. The major components of this sensor are as

shown in Figure 2. The photons which are to be detected pass

through an ON Semiconductor proprietary color filter

limiting extraneous photons and thus performing as a band

pass filter on the incident wave front. The filter only

transmits photons in the visible spectrum which are

primarily detected by the human eye. The photo response of

this sensor is as shown in Figure 5.

The ambient light signal detected by the photo diode is

converted to digital signal using a variable slope integrating

ADC with a resolution of 16−bits, unsigned. The ADC value

interface block.

room temperature (25

°C).

(eq. 1)

Where:

For example let:

(eq. 2)

Modes of Operation

The NOA1305 can be placed in any of the following

bus:

1. Interrupt driven mode

2. Polling mode

3. Power−down mode

In the interrupt driven mode, once the NOA1305 is

light intensity goes above the value programmed in the

interrupt threshold register. When this occurs, the device

master host to read the ALS count from the device.

In polling mode, interrupts are typically disabled, but the

master host reads out the most recent count whenever it

desires to do so, typically in a timed repeat loop.

In power−down mode, the NOA1305 stops taking

ambient light measurements and powers down most of the

internal circuitry and the INT pin is deactivated. Power is

maintained to preserve the register values (static memory)

power−on command to the NOA1305.

single register read and write operations, in addition to block

read and block write operations. All data transactions on the

bus are 8 bits long. Each data byte transmitted is followed by

an acknowledge bit. Data is transmitted with the MSB first.

followed by the seven bit slave address (NOA1305 = 0x39)

and the write(0) command bit. The NOA1305 will

acknowledge this byte transfer with an appropriate ACK.

Next the master will send the 8 bit register address to be

written to. Again the NOA1305 will acknowledge reception

with an ACK. Finally, the master will begin sending 8 bit

data segment(s) to be written to the NOA1305 register bank.

The NOA1305 will send an ACK after each byte and

increment the address pointer by one in preparation for the

next transfer. Write transactions are terminated with either

START).

78

8

A[6:0]

D[7:0]

D[7:0]

WRITE ACK

ACK

ACK

Device

Address

Register

Address

Register

Data

Start

Condition

Stop

Condition

011 1001 0

0

00000000

0000 0110 00

0x72