Sense

High

Sense

Low

1V

VIO/VBAT

Trip Point

Decode

Current Control

Register

AVAGO APDS-9005

2.2 k:

Default TRIP POINTS

1000 LUX for Bright Ambient (900 mV) (Bright Outdoor Lighting)

No Flash

100 to 1000 LUX for Indoor Ambient (90 mV) (Office Lighting)

70% Full-Scale Flash

0 to 100 LUX for Low Ambient (Night or Movie Theater)

Full-Scale Flash

1V

1 PF

Sense

High

Sense

Low

1V

VBIAS/VIO

Trip Point

Decode

Current Control

Register

R1

1V

RT

31

LM3550

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SNVS569C – MAY 2009 – REVISED OCTOBER 2016

Product Folder Links: LM3550

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Figure 51. Thermistor Voltage Divider and Sensing Circuit

8.2.2.1.4.2

Ambient Light Sensor

If the ALD/TEMP pin is not used for ambient/LED temperature monitoring, it can be used for ambient light

detection. The LM3550 provides three regions of current control based upon ambient conditions. The three

regions are defined using the Sense High and Sense Low Registers to set the zone boundaries (user-

configurable from 0 to 1 V). Most ambient light sensors are reverse-biased diodes that leak current proportional

to the amount of ambient light reaching the sensor. This current is then translated into a voltage by using a

resistor in series with the light sensor. The voltage-setting resistor varies based upon the desired ambient

detection range and manufacturer.

Most ambient light sensors suggest placing a capacitor in parallel with the voltage-setting resistor in order to help

filter the 50-, 60-Hz noise generated by fluorescent overhead lighting. This capacitor can range from no capacitor

up to 10 µF. The key is to filter the noise so that the peak-to-peak voltage is less than 16 mV (LSB size of the

ALD/TEMP sense high and sense low settings). Refer to the data sheet of the ambient light sensor for the

recommended capacitor value.