LM3532TMX-40ANOPB National Semiconductor Corporation, LM3532TMX-40ANOPB Datasheet - Page 16

• Manufacturer Part Number: LM3532TMX-40ANOPB
• Description: High Efficiency White Led Driver With Programmable Ambient Light Sensing Capability And I2c-compatible Interface
• Manufacturer: National Semiconductor Corporation

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Output Configuration
Register
Bits[1:0] = 00, assigns
ILED1 to Control Bank A
Bits[3:2] = 00 assigns
ILED2 to Control Bank A
Bits[5:4] = 00, assigns
ILED3 to Control Bank A
AMBIENT LIGHT SENSOR CURRENT CONTROL
In Ambient Light Sensor (ALS) Current Control the LM3532’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 am-
bient light sensors. Each ALS input has an active input voltage
range of 0 to 2V.
ALS LIGHT SENSOR RESISTORS
The LM3532 offers 32 separate programmable internal resis-
tors at the ALS1 and ALS2 inputs. These resistors take the
ambient light sensor's output current and convert it into a volt-
age. The value of the resistor selected is typically chosen
such that the ambient light sensors output voltage swing goes
from 0 to 2V across the intended measured ambient light
(LUX) range. The ALS resistor values are programmed via
the ALS1 and ALS2 Resistor select registers (see
The code to resistor selection (assuming a 2V full-scale volt-
age range) is shown in the following equation:
Each higher code in the specific ALS Resistor Select Register
increases the allowed ALS sensor current by 54 µA ( for a 2V
Current Sink
Assignment
Control A Brightness
Configuration
Register Bits [4:2]
000 selects Control A
Zone Target 0 as
brightness register
001 selects Control A
Zone Target 1
brightness register
010 selects Control A
Zone Target 2
brightness register
011 selects Control A
Zone Target 3
brightness register
1XX selects Control A
Zone Target 4
brightness register
Brightness Register
TABLE 1. I
2
C Current Control + PWM Bit Settings (For Control Bank A)
Control A PWM
Register Bit[0]
0 selects PWM1
1 selects PWM2
Table
PWM Select
15).
16
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. Alterna-
tively, ALS Resistor Select Register Code 00000 will set the
specific ALS input to high impedance.
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 cur-
rent 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 2V. This gives a 2V/255 = 7.8 mV
per bit.
mapping.
Control A PWM Register
Bit[2] is PWM enable when
Control A Zone Target 0 is
configured as the brightness
register
Bit[3] is PWM enable when
Control A Zone Target 1 is
configured as the brightness
register
Bit[4] is PWM enable when
Control A Zone Target 2 is
configured as the brightness
register
Bit[5] is PWM enable when
Control A Zone Target 3 is
configured as the brightness
register
Bit[6] is PWM enable when
Control A Zone Target 4 is
configured as the brightness
register
Figure 5
PWM Enable
describes the ambient light to brightness
Current Sink Enable
Control Enable
Register Bit [0]
0 = Bank A Disabled
1 = Bank A Enabled