LM3532TMX-40ANOPB National Semiconductor Corporation, LM3532TMX-40ANOPB Datasheet - Page 18

• 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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PWM ENABLED FOR A PARTICULAR ZONE
The active PWM input for a specified Control Bank can be
enabled/disabled for each ALS Brightness Zone. This is done
via bits[6:2] of the corresponding Control A, B, or C PWM
Registers (see
assuming Control Bank A is being used, then to make the
PWM input active in Zones 0, 2, and 4, but not active in Zones
ALS INPUT SELECT and ALS ADC INPUT
The internal 8-bit ADC digitizes the active ambient light sen-
sor inputs (ALS1 or ALS2). The active ALS input is deter-
mined by the bit settings of the ALS input select bits, bits [7:6]
in the ALS Configuration register. The active ALS input can
be the average of ALS1 and ALS2, the maximum of ALS1 and
ALS2, ALS1 only, or ALS2 only. Once the ALS input select
stage selects the active ALS input, the result is sent to the
internal 8-bit ADC. For example, if the active ALS input select
is set to be the average of ALS1 and ALS2, then the voltage
ALS ADC READBACK
The digitized value of the LM3532's ADC is read back from
the ADC Readback Register. Once the ALS is enabled the
Table
6,
Table
7, and
Table
FIGURE 7. ALS Functional Block Diagram
8). For example,
FIGURE 8. ADC Timing
18
1, and 3, bits[6:2] of the Control A PWM Register would be
set to (1, 0, 1, 0, 1).
ALS OPERATION
Figure 7
ambient light sensor interface.
at ALS1 and ALS2 is first averaged, then applied to the ADC.
The output of the ADC (ADC Register) will be the digitized
average value of ALS1 and ALS2.
The LM3532's internal ADC samples at 7.143 ksps. ADC tim-
ing is shown in
Configuration Register bit [3] = 1) the ADC begins sampling
and converting the active ALS input. Each conversion takes
140 µs. After each conversion the ADC register is updated
with new data.
ADC begins converting the active ALS input and updating the
ALS Readback Register every 140 µs. The ADC Readback
register contains the updated data after each conversion.
shows a functional block diagram of the LM3532's
Figure
8. When the ALS is Enabled (ALS
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