Maxim Integrated MAX86140 - Detailed Description of Software; MAX86140 Max Sample Rates; MAX86141 Max Sample Rates; Sample Rate

Maxim Integrated │ 15
www.maximintegrated.com
Evaluates: MAX86140 and MAX86141
MAX86140/MAX86141
Evaluation System
Detailed Description of Software
The EVSYS includes two sensor PCBs. Each
contains MAX86140/MAX86141 optical AFE, a
3-axis accelerometer together with a photodiode(s)
and LED(s). MAX86140_OSB_EVSYS comes with a
discreet photodiode (VEMD5080X01) and two green
LEDs (Osram CT DBLP31.12-5C8C-56-J6Q6), while
MAX86141_OSB_EVSYS comes with two discreet
photodiodes (VEMD5080X01), and a green LED (Osram
CT DBLP31.12-5C8C-56-J6Q6). The EVSYS allows raw
optical and accelerometer data to be sampled and
transferred to the GUI for both dynamic viewing and logging
for later analysis. The EVSYS micro controller PCB is used
to do SPI to BLE communication, transporting the raw
optical and accelerometer data to the PC via BLE.
Most functionality of the MAX86140/MAX86141 has
been mapped to the GUI so the wide variety of applications
supported by the MAX86140/MAX86141 can be
rapidly explored. The following is a brief description of this
functionality options.
Sample Rate
The sample rate can take on values between 8 to
4096sps. The dual pulse mode option are modes where
the samples are unevenly spaced and averaged to
improve the ambient rejection of mains line rate ambient
signals.
Table 1 and Table 2 shows the maximum supported
sampling rates (in Sps) for the MAX86140 and MAX86141
respectively for the given number of exposure sequences
and use of accelerometer. The maximum sample rate is
limited by the BLE protocol, not the AFE itself.
For a given sample rate, the number listed can be
increased to the next available MAX86140/MAX86141
sample rate (i.e., 500Sps → 512Sps).
Integration Pulse Width
The pulse width setting adjusts the integration time of an
exposure. The MAX86140\MAX86141 supports exposure
integration times of 14.8μs, 29.4μs, 58.7μs, and 117.3μs.
The exposure pulse width is a critical parameter in any
optical measurement. Longer exposures allow for more
optical photons to be integrated but also increase system
power and reduce ambient rejection capability.
Burst Rate
When Burst Mode is disabled, PPG data conversions
are continuous at the sample rate dened by PPG_SR
register, When Burst mode is enabled, a burst of PPG
data conversions occurs at the sample rate dened by
Sample Rate (PPG_SR) register. Number of conversion
in the burst is dened by the SMP_AVE register. Average
data from the burst of data conversions is pushed to the
FIFO at the rate of burst average rate. The burst repeats
at the rate of 8, 32, 84, or 256Hz can be congured in
burst average eld. The burst average rate eld denes
the rate at which data is pushed into the FIFO. If the
number of conversions cannot be accommodated, the
device will use the next highest number of conversions. If
the e󰀨ective sample rate is too slow to accommodate the
burst rate programmed, BURST_EN is automatically set
to 0, and the device runs in continuous mode.
Ambient Light Cancellation
The on-chip Ambient Light Cancellation incorporates a
proprietary scheme to cancel ambient light generated
photo diode current, allowing the sensor to work in high
ambient light conditions.
ADC Full-Scale Range
The MAX86140\MAX86141 optical channel has 4 full-
scale ranges. These ranges are 4μA, 8μA, 16μA, and
32μA.
Table 1. MAX86140 Max Sample Rates
(Sps)
Table 2. MAX86141 Max Sample Rates
(Sps)
ACCELEROMETER
WITH WITHOUT
# OF SEQUENCES
1 500 1000
2 500 1000
3 250 500
4 250 500
5 125 250
6 125 250
ACCELEROMETER
WITH WITHOUT
# OF SEQUENCES
1 500 1000
2 250 500
3 125 250
4 125 125
5 125 125
6 62.5 125