LP3954 Datasheet, PDF (27/56 Pages) National Semiconductor (TI) – Advanced Lighting Management Unit

Ambient Light and Temperature
Measurement with LP3954
The Analog-to-Digital converter (ADC) in the Audio Syn-
cronization block can be also used for ambient light measure-
ment or temperature measurement.
The selection between these modes is controlled with input
selector bits INPUT_SEL[1:0] as follows
INPUT_SEL[1:0]
Mode
00
Audio synchronization
01
Temperature measurement
(voltage input)
10
Ambient light measurement
(current input)
11
No input
AMBIENT LIGHT MEASUREMENT
The ambient light measurement requires only one external
component: Ambient light sensor (photo transistor or diode).
The ADC reads the current level at ASE pin and converts the
result in digital word. User can read the ADC output from the
ADC output register. The known ambient light condition al-
lows user to set the backlight current to optimal level thus
saving power especially in low light and bright sunlight con-
dition.
TEMPERATURE MEASUREMENT
The temperature measurement requires two external compo-
nents: resistor and thermistor (resistor that has known tem-
perature vs resistance curve). The ADC reads the voltage
level at ASE pin and converts the result in digital word. User
can read the ADC output from register. The known tempera-
ture allows for example to monitor the temperature inside the
display module and decrease the current level of the LEDs if
temperature raises too high. This function may increase life-
time of LEDs in some applications.
20132242
Temperature sensor connection example
20132241
20132263
ADC Code vs Input Voltage
in temperature measurement mode
20132264
ADC Code vs Input Current
in light measurement mode
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