LM3532 datasheet(15/52 Pages) TI2

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RALS_ =

54 PA

u Code

LM3532

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SNVS653E – JULY 2011 – REVISED AUGUST 2015

Device Functional Modes (continued)

Table 1. I2C Current Control and PWM Bit Settings (For Control Bank A)

CURRENT SINK

BRIGHTNESS

CURRENT SINK

PWM SELECT

PWM ENABLE

ASSIGNMENT

ENABLE

Output Configuration

Control A Brightness

Control A PWM

Control A PWM Register

Control Enable

Configuration Register

Bit[2] is PWM enable when Control Register Bit [0]

Bits[1:0] = 00, assigns

Bits [4:2]

0 selects PWM1

A Zone Target 0 is configured as

0 = Bank A Disabled

ILED1 to Control Bank A

000 selects Control A

1 selects PWM2

the brightness register

1 = Bank A Enabled

Bits[3:2] = 00 assigns

Zone Target 0 as

Bit[3] is PWM enable when Control

ILED2 to Control Bank A

brightness register

A Zone Target 1 is configured as

Bits[5:4] = 00, assigns

001 selects Control A

the brightness register

ILED3 to Control Bank A

Zone Target 1

Bit[4] is PWM enable when Control

brightness register

A Zone Target 2 is configured as

010 selects Control A

the brightness register

Zone Target 2

Bit[5] is PWM enable when Control

brightness register

A Zone Target 3 is configured as

011 selects Control A

the brightness register

Zone Target 3

Bit[6] is PWM enable when Control

brightness register

A Zone Target 4 is configured as

1XX selects Control A

the brightness register

Zone Target 4

brightness register

7.4.10 Ambient Light Sensor Current Control

In Ambient Light Sensor (ALS) current control the LM3532 device’s backlight current is automatically set based

upon the voltage at the ambient light sensor inputs (ALS1 and/or ALS2). These inputs are designed to connect to

the outputs of analog ambient light sensors. Each ALS input has an active input voltage range of 0 to 2 V.

7.4.10.1 ALS Resistors

The LM3532 offers 32 separate programmable internal resistors at the ALS1 and ALS2 inputs. These resistors

take the ambient light sensor's output current and convert it into a voltage. The value of the resistor selected is

typically chosen such that the ambient light sensors output voltage swing goes from 0 to 2 V across the intended

measured ambient light (LUX) range. The ALS resistor values are programmed via the ALS1 and ALS2 Resistor

select registers (see Table 15). The code-to-resistor selection (assuming a 2-V full-scale voltage range) is shown

in Equation 3:

(3)

Each higher code in the specific ALS Resistor Select Register increases the allowed ALS sensor current by 54

µA ( for a 2-V full-scale). When the ALS is disabled (ALS Configuration Register bit [3] = 0) the ALS inputs are

set to a high impedance mode no matter what the ALS resistor selection is. Alternatively, ALS Resistor Select

7.4.10.2 Ambient Light Zone Boundaries

The LM3532 provides 5 ambient light brightness zones which are defined by 4 zone boundary registers. The

LM3532 has one set of zone boundary registers that is shared globally by all control banks. As the voltage at the

ALS input changes in response to the ambient light sensors received light, the ALS voltage transitions through

the 5 defined brightness zones. Each brightness zone can be assigned a brightness target via the 5 zone target

registers. Each control bank has its own set of zone target registers. Therefore, in response to changes in a

Brightness Zone at the ALS input, the LED current can transition to a new brightness level. This allows for backlit

LCD displays to reduce the LED Current when the ambient light is dim or increase the LED current when the

ambient light increases. Each zone boundary register is 8 bits with a full-scale voltage of 2 V. This gives 2 V/255

= 7.8 mV per bit. Figure 14 describes the ambient light to brightness mapping.

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