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Evaluates: MAX86140 and MAX86141
MAX86140/MAX86141
Evaluation System
Sample Average
The MAX86140\MAX86141 has the capability to do
sample averaging of 2 ~ 128 samples internally. This
feature is useful if more optical energy is needed to make
a low perfusion measurement but the data rate across the
interface or the processing power in a host micro is not
desirable. This mode is also useful to further suppress the
mains line noises in indoor lighting conditions.
PD Bias
The MAX86140\MAX86141 provides multiple photo diode
biasing options. These options allow the MAX86140\
MAX86141 to operate with a large range of photo diode
capacitance. The PDBIAS values adjust the PD_IN bias
point impedance to ensure that the photo diode settles
rapidly enough to support the sample timing. PDBIAS is
configured depending on the Capacitance (CPD) of the
photodiode used.
Note: PD2 configuration is only available for MAX86141.
LED Sequence Control (FIFO Time Slots)
The LED Sequence Control specifies the data acquisition
sequence that the internal state machine controller will
follow and where the converted data will be mapped into
the FIFO.
Each FIFO field can be applied to one measurement.
Acquired data can be from LED1, LED2, or LED3 (optical
exposure from LED1~3) illuminated independently.
The LED1&LED2, LED1&LED3, LED2&LED3, and
LED1&LED2&LED3 are optical exposures from LEDs
illuminated simultaneously. The other options are Ambient
(optical data with no exposure, just ambient illumination)
or None (skip this acquisition). The LED4-6 (Mux Control)
are not supported with the sensor PCB. If a custom sensor
board with MUX is used, LED4, LED5 and LED6 can also
be configured. Only LED1 and LED2 are available in this
EVSYS.
The exposure sequence will be the entry in Sequence
1 (LEDC1) slot, Sequence 2 (LEDC 2) slot, Sequence 3
(LEDC3), Sequence 4 (LEDC4), Sequence 5 (LEDC5)
slot then Sequence 6 (LEDC6) slot. This sequence
will repeat for each sample instance. Each Sequence
if programmed, will be plot in the PPG Plot x tabs
respectively as shown in
Figure 15
.
Please refer to the MAX86140/MAX86141 datasheet
under FIFO Configuration Section for details.
LED Driver Configurations
Each of the three LED drivers has a Range and Peak
LED Current setting. There are 4 full-scale range settings
31mA, 62mA, 93mA and 124mA. Each range has an 8-bit
current source DAC. The Peak LED Current box allows
for an actual current to be entered. The nearest available
DAC current is selected and displayed in the field.
LED Settling Time
The LED Settling Time is the time prior to the start of
integration (pulse-width setting) that the LED is turned
on. There are four settlings, 12μs, 8μs, 6μs and 4μs. This
time is necessary to allow the LED driver to settle before
integrating the exposure photo current.
GPIO Control
Various options of GPIO controls are available on
MAX86140. For the EVSYS, when set to GPIO options
2, the sample rate will be triggered by the on-board
accelerometer.
Please refer to the MAX86140/MAX86141 datasheet
under GPIO Configuration Section for details.
Accelerometer Configuration
The on-board accelerometer can be enabled or disabled
by using the GUI. Supported accelerometer Full-Scale
Range are ±2g, ±4g, ±8g and ±16g. The output data of
the accelerometer can also be configured from 15.63Hz
to 2000Hz when used with GPIO Control Option 2.
Picket Fence Configuration
Under typical situations, the rate of change of ambient
light is such that the ambient signal level during exposure
can be accurately predicted and high levels of ambient
rejection are obtained. However, it is possible to have
situations where the ambient light level changes extremely
rapidly, for example when in a car with direct sunlight
exposure passes under a bridge and into a dark shadow.
In these situations, it is possible for the on-chip ambient
light correction (ALC) circuit to fail and produce and
erroneous estimation of the ambient light during the
exposure interval. The optical controller has a built-in
algorithm, called the picket fence function, that can
correct for these extreme conditions on the ALC circuit.
Please refer to the MAX86140/MAX86141 datasheet
under Picket Fence Detect-and-Replace Function Section
for details.
