Data Sheet
Proximity Mode Interrupt Threshold (0x30)
This register sets the IR ADC count that will trigger the beginning of particle-sensing mode. The threshold is defined as
the 8 MSBs of the ADC count. For example, if PROX_INT_THRESH[7:0] = 0x01, then an ADC value of 1023 (decimal) or
higher triggers the PROX interrupt. If PROX_INT_THRESH[7:0] = 0xFF, then only a saturated ADC triggers the interrupt.
Applications Information
Sampling Rate and Performance
The maximum sample rate for the ADC depends on the selected pulse width, which in turn, determines the ADC resolution.
For instance, if the pulse width is set to 69µs then the ADC resolution is 15 bits, and all sample rates are selectable. However,
if the pulse width is set to 411µs, then the samples rates are limited. The allowed sample rates for both particle-sensing modes
are summarized in Table 11 and Table 12.
Power Considerations
The LED waveforms and their implication for power supply design are discussed in this section.
The LEDs in the MAX30105 are pulsed with a low duty cycle for power savings, and the pulsed currents can cause ripples
in the V
LED+
power supply. To ensure these pulses do not translate into optical noise at the LED outputs, the power supply
must be designed to handle these. Ensure that the resistance and inductance from the power supply (battery, DC/DC
converter, or LDO) to the pin is much smaller than 1Ω, and that there is at least 1µF of power supply bypass capacitance
to a good ground plane. The capacitance should be located as close as physically possible to the IC.
Table 11. Particle-Sensing Mode
Using 2 LEDs (Allowed Settings)
Table 12. Particle-Sensing Mode
Using 1 LEDs (Allowed Settings)
REGISTER B7 B6 B5 B4 B3 B2 B1 B0
REG
ADDR
POR
STATE
R/W
Proximity
Interrupt
Threshold
PROX_INT_THRESH[7:0] 0x30 0x00 R/W
SAMPLES
PER
SECOND
PULSE WIDTH (µs)
SAMPLES
PER
SECOND
PULSE WIDTH (µs)
69 118 215 411 69 118 215 411
50 O O O O 50 O O O O
100 O O O O 100 O O O O
200 O O O O 200 O O O O
400 O O O O 400 O O O O
800 O O O 800 O O O O
1000 O O 1000 O O O O
1600 O 1600 O O O
3200 3200 O
Resolution
(bits)
15 16 17 18
Resolution
(bits)
15 16 17 18
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MAX30105 High-Sensitivity Optical Sensor
for Smoke Detection Applications