ISL29020 查看數據表（PDF） - Renesas Electronics

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ISL29020

A Low Power, High Sensitivity, Light-to Digital Sensor With I2C Interface

Renesas Electronics 

ISL29020

Pin Descriptions

PIN NUMBER

1

2

3

4

5

6

PIN NAME

VDD

GND

REXT

A0

SCL

SDA

DESCRIPTION

Positive supply; connect this pin to a 2.25V to 3.3V supply.

Ground pin.

External resistor pin for ADC reference; connect this pin to ground through a (nominal) 500k resistor.

Bit 0 of I2C address; ground or tie this pin to VDD. No floating.

I2C serial clock

I2C serial data

The I2C bus lines can be pulled from 1.7V to above VDD, 3.6V max.

Principles of Operation

Photodiodes and ADC

The ISL29020 contains two photodiode arrays which convert

light into current. The spectral response for ambient light

sensing and IR sensing is shown in Figure 8 in the “Typical

Performance Curves” on page 9. After light is converted to

current during the light signal process, the current output is

converted to digital by a single built-in 16-bit Analog-to-Digital

Converter (ADC). An I2C command reads the ambient light or IR

intensity in counts.

The converter is a charge-balancing integrating type 16-bit ADC.

The chosen method for conversion is best for converting small

current signals in the presence of an AC periodic noise. A 100ms

integration time, for instance, highly rejects 50Hz and 60Hz power

line noise simultaneously. See “Integration Time or Conversion

Time” on page 6 and “Noise Rejection” on page 7.

The built-in ADC offers user flexibility in integration time or

conversion time. There are two timing modes: Internal Timing

Mode and External Timing Mode. In Internal Timing Mode,

integration time is determined by an internal oscillator (fOSC), and

the n-bit (n = 4, 8, 12,16) counter inside the ADC. In External

Timing Mode, integration time is determined by the time between

two consecutive I2C External Timing Mode commands. See

“External Timing Mode” on page 6. A good balancing act of

integration time and resolution depending on the application is

required for optimal results.

The ADC has I2C programmable ranges to dynamically

accommodate various lighting conditions. For very dim

conditions, the ADC can be configured at its lower range

(Range 1). For bright conditions, the ADC can be configured at

its higher range (Range 2).

I2C Interface

There are three 8-bit registers available inside the ISL29020.

The command register defines the operation of the device. The

command register does not change until the register is

overwritten. The two data registers are Read-Only for 16-bit

ADC output or timer output. The data registers contain the

ADC's or timer’s latest digital output.

The ISL29020’s I2C interface slave address can be selected as

1000100 or 1000101 by connecting A0 pin to GND or VDD,

respectively. When 1000100x or 1000101x with x as R or W is

sent after the Start condition, this device compares the first

seven bits of this byte to its address and matches.

Figure 1 shows a sample one-byte read. Figure 2 shows a

sample one-byte write. Figure 3 shows a sync_I2C timing

diagram sample for externally controlled integration time. The

I2C bus master always drives the SCL (clock) line, while either

the master or the slave can drive the SDA (data) line. Every I2C

transaction begins with the master asserting a start condition

(SDA falling while SCL remains high). The following byte is

driven by the master, and includes the slave address and

read/write bit. The receiving device is responsible for pulling

SDA low during the acknowledgement period. Every I2C

transaction ends with the master asserting a stop condition

(SDA rising while SCL remains high).

For more information about the I2C standard, please consult

the Philips® I2C specification documents.

Low-Power Operation

The ISL29020 initial operation is at the power-down mode after

a supply voltage is provided. The data registers contain the

default value of 0. When the ISL29020 receives an I2C

command to do a one-time measurement from an I2C master,

it will start light sensing and ADC conversion. It will go to the

power-down mode automatically after one conversion is

finished and keep the conversion data available for the master

to fetch anytime afterwards. The ISL29020 will continuously do

light sensing and ADC conversion if it receives an I2C

command of continuous measurement. It will continuously

update the data registers with the latest conversion data. It will

go to the power-down mode after it receives the I2C command

of power-down.

FN6505 Rev 1.00

August 20, 2009

Page 3 of 11

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