Data Sheet

Particle-Sensing Temperature Compensation

The MAX30105 has an accurate on-board temperature

sensor that digitizes the IC’s internal temperature upon

command from the I

C master.

Table 13 shows the correlation of red LED wavelength

versus the temperature of the LED. Since the LED die

heats up with a very short thermal time constant (tens of

microseconds), the LED wavelength should be calculated

according to the current level of the LED and the temperature

of the IC. Use Table 13 to estimate the temperature.

Red LED Current Settings vs. LED Temperature

Rise

Add estimated temperature rise to the module tempera-

ture reading to estimate the LED temperature and output

wavelength. The LED temperature estimate is valid even

with very short pulse widths, due to the fast thermal time

constant of the LED.

Interrupt Pin Functionality

The active-low interrupt pin pulls low when an interrupt is

triggered. The pin is open-drain, which means it normally

requires a pullup resistor or current source to an external

voltage supply (up to +5V from GND). The interrupt pin is

not designed to sink large currents, so the pullup resistor

value should be large, such as 4.7kΩ.

Table 13. RED LED Current Settings vs. LED Temperature Rise

RED LED CURRENT SETTING

RED LED DUTY CYCLE (% OF LED

PULSE WIDTH TO SAMPLE TIME)

ESTIMATED TEMPERATURE

RISE (ADD TO TEMP SENSOR

MEASUREMENT) (°C)

0001 (0.2mA) 8 0.1

1111 (50mA) 8 2

0001 (0.2mA) 16 0.3

1111 (50mA) 16 4

0001 (0.2mA) 32 0.6

1111 (50mA) 32 8

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MAX30105 High-Sensitivity Optical Sensor

for Smoke Detection Applications