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MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
General Description
Benefits and Features
The MAX30101 is an integrated pulse oximetry and heartrate monitor module. It includes internal LEDs, photodetectors, optical elements, and low-noise electronics
● Heart-Rate Monitor and Pulse Oximeter Sensor in
LED Reflective Solution
● Tiny 5.6mm x 3.3mm x 1.55mm 14-Pin Optical Module
• Integrated Cover Glass for Optimal, Robust
Performance
with ambient light rejection. The MAX30101 provides a
complete system solution to ease the design-in process
for mobile and wearable devices.
The MAX30101 operates on a single 1.8V power supply
and a separate 5.0V power supply for the internal LEDs.
Communication is through a standard I2C-compatible
interface. The module can be shut down through software
with zero standby current, allowing the power rails to
remain powered at all times.
● Fast Data Output Capability
• High Sample Rates
● Robust Motion Artifact Resilience
• High SNR
Applications
●
●
●
●
● Ultra-Low-Power Operation for Mobile Devices
• Programmable Sample Rate and LED Current for
Power Savings
• Low-Power Heart-Rate Monitor (< 1mW)
• Ultra-Low Shutdown Current (0.7μA, typ)
● -40°C to +85°C Operating Temperature Range
Wearable Devices
Fitness Assistant Devices
Smartphones
Tablets
Ordering Information appears at end of data sheet.
System Diagram
APPLICATIONS
HOST (AP)
ELECTRICAL
MAX30101
HARDWARE FRAMEWORK
DRIVER
OPTICAL
I2 C
LED DRIVERS
HUMAN
SUBJECT
RED/IR/GREEN
LED
DIGITAL NOISE
CANCELLATION
DATA
FIFO
18-BIT
CURRENT ADC
AMBIENT LIGHT
CANCELLATION
19-8453; Rev 3; 6/20
PHOTO
DIODE
PACKAGING
COVER GLASS
AMBIENT
LIGHT
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Absolute Maximum Ratings
VDD to GND........................................................... -0.3V to +2.2V
GND to PGND ....................................................... -0.3V to +0.3V
VLED+ to PGND .................................................... -0.3V to +6.0V
All Other Pins to GND ........................................... -0.3V to +6.0V
Output Short-Circuit Current Duration ........................ Continuous
Continuous Input Current into Any Terminal ..................... ±20mA
Continuous Power Dissipation (TA = +70°C) OESIP (derate
5.5mW/°C above +70°C) ..................................................440mW
Operating Temperature Range .............................-40°C to +85°C
Junction Temperature ......................................................... +90°C
Soldering Temperature (reflow) ........................................ +260ºC
Storage Temperature Range .............................. -40ºC to +105ºC
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the
device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for
extended periods may affect device reliability.
Package Information
14 OESIP
Package Code
F143A5+1
Outline Number
21-1048
Land Pattern Number
90-0602
THERMAL RESISTANCE, FOUR-LAYER BOARD
Junction-to-Ambient (θJA)
180°C/W
Junction-to-Case Thermal Resistance (θJC)
150°C/W
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages.
Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different
suffix character, but the drawing pertains to the package regardless of RoHS status.
Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a
four-layer board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/
thermal-tutorial.
Electrical Characteristics
(VDD = 1.8V, VLED+ = 5.0V, TA = +25°C, min/max are from TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA =
25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Guaranteed by RED and IR count
tolerance
1.7
1.8
2.0
V
Guaranteed by PSRR of LED driver (RED
and IR LED only)
3.1
3.3
5.0
Guaranteed by PSRR of LED driver
(GREEN LED only). TA = 25°C
4.5
5.0
5.5
SpO2 and HR mode, PW = 215µs, 50sps
600
1100
IR only mode, PW = 215µS, 50sps
600
1100
TA = +25°C, MODE = 0x80
0.7
2.5
POWER SUPPLY
Power-Supply Voltage
LED Supply Voltage
VLED+ to PGND
Supply Current
Supply Current in
Shutdown
VDD
VLED+
IDD
ISHDN
V
µA
µA
PULSE OXIMETRY/HEART-RATE SENSOR CHARACTERISTICS
ADC Resolution
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18
19-8453
bits
Maxim Integrated | 2
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Electrical Characteristics (continued)
(VDD = 1.8V, VLED+ = 5.0V, TA = +25°C, min/max are from TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA =
25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Red ADC Count (Note
2)
REDC
LED1_PA = 0x0C, LED_PW = 0x01,
SPO2_SR = 0x05,
ADC_RGE = 0x00
IR ADC Count (Note 2)
IRC
LED2_PA = 0x0C, LED_PW = 0x01,
SPO2_SR = 0x05
ADC_RGE = 0x00
65536
Counts
LED3_PA = LED4_PA = 0x24, LED_PW
= 0x01,
SPO2_SR = 0x05, ADC_RGE = 0x00
65536
Counts
LED1_PA = LED2_PA = 0x00, LED_PW
= 0x03, SPO2_SR = 0x01 ADC_RGE =
0x02
30
128
Counts
LED1_PA = LED2_PA = 0x00, LED_PW
= 0x03, SPO2_SR = 0x01 ADC_RGE =
0x03
0.01
0.05
% of FS
Green ADC Count (Note
2)
Dark Current Count
DC Ambient Light
Rejection (Note 3)
ADC Count—PSRR
(VDD)
GRNC
LED_DCC
ALR
PSRRVDD
ADC counts with
finger on sensor
under direct
sunlight (100K lux),
ADC_RGE = 0x3,
LED_PW = 0x03,
SPO2_SR = 0x01
Red LED
ADC counts with
finger on sensor
under direct
sunlight (100K lux),
ADC_RGE = 0x3,
LED_PW = 0x03,
SPO2_SR = 0x02
IR LED
PSRRLED
ADC Clock Frequency
CLK
Counts
2
1.7V < VDD < 2.0V,
LED_PW = 0x00, SPO2_SR = 0x05
0.25
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INT
3.1V < VLED+ < 5.0V, LED1_PA =
LED2_PA = 0x0C,
LED_PW = 0x01, SPO2_SR = 0x05
0.05
4.5V < VLED+ < 5.5V, TA = 25°C
LED3_PA = LED4_PA = 0x24, LED_PW
= 0x01, SPO2_SR = 0x05
0.05
% of FS
LSB
1
% of FS
1
10
10.2
10.48
LED_PW = 0x00
69
LED_PW = 0x01
118
LED_PW = 0x02
215
LED_PW = 0x03
411
19-8453
1
10
Frequency = DC to 100kHz, 100mVP-P
ADC Integration Time
(Note 3)
Counts
2
Frequency = DC to 100kHz, 100mVP-P
ADC Count—PSRR
(LED Driver Outputs)
65536
LSB
10.8
MHz
µs
Maxim Integrated | 3
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Electrical Characteristics (continued)
(VDD = 1.8V, VLED+ = 5.0V, TA = +25°C, min/max are from TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA =
25°C.) (Note 1)
PARAMETER
Slot Timing (Timing
Between Sequential
Channel Samples; e.g.,
Red Pulse Rising Edge
To IR Pulse Rising
Edge)
SYMBOL
INT
CONDITIONS
MIN
TYP
LED_PW = 0x00
427
LED_PW = 0x01
525
LED_PW = 0x02
720
LED_PW = 0x03
1107
MAX
UNITS
µs
COVER GLASS CHARACTERISTICS (Note 3)
Hydrolytic Resistance
Class
Per DIN ISO 719
HGB 1
IR LED CHARACTERISTICS (Note 3)
LED Peak Wavelength
λP
ILED = 20mA, TA = +25°C
Full Width at Half Max
Δλ
ILED = 20mA, TA = +25°C
870
880
30
900
nm
Forward Voltage
VF
ILED = 20mA, TA = +25°C
1.4
V
Radiant Power
PO
ILED = 20mA, TA = +25°C
6.5
mW
nm
RED LED CHARACTERISTICS (Note 3)
LED Peak Wavelength
λP
ILED = 20mA, TA = +25°C
650
660
670
nm
Full Width at Half Max
Δλ
ILED = 20mA, TA = +25°C
20
nm
Forward Voltage
VF
ILED = 20mA, TA = +25°C
2.1
V
Radiant Power
PO
ILED = 20mA, TA = +25°C
9.8
mW
GREEN LED CHARACTERISTICS (Note 3)
LED Peak Wavelength
λP
ILED = 50mA, TA = +25°C
Full Width at Half Max
Δλ
ILED = 50mA, TA = +25°C
530
537
545
Forward Voltage
VF
ILED = 50mA, TA = +25°C
3.3
V
Radiant Power
PO
ILED = 50mA, TA = +25°C
17.2
mW
35
nm
nm
PHOTODETECTOR CHARACTERISTICS (Note 3)
Spectral Range of
Sensitivity
Radiant Sensitive Area
Dimensions of Radiant
Sensitive Area
Λ > 30% QE
QE: Quantum Efficiency
640
980
nm
A
1.36
mm2
LxW
1.38 x
0.98
mm x
mm
INTERNAL DIE TEMPERATURE SENSOR
Temperature ADC
Acquisition Time
TT
TA = +25°C
29
ms
Temperature Sensor
Accuracy
TA
TA = +25°C
±1
°C
Temperature Sensor
Minimum Range
TMIN
-40
°C
Temperature Sensor
Maximum Range
TMAX
85
°C
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19-8453
Maxim Integrated | 4
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Electrical Characteristics (continued)
(VDD = 1.8V, VLED+ = 5.0V, TA = +25°C, min/max are from TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA =
25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
0.3 x
VDD
V
DIGITAL INPUTS (SCL, SDA)
Input Logic-Low Voltage
VIL
Input Logic-High Voltage
VIH
0.7 x
VDD
V
VHYS
0.5 x
VDD
Input Leakage Current
IIN
±0.1
Input Capacitance
CIN
10
Input Hysteresis
V
±1
µA
pF
DIGITAL OUTPUTS (SDA, INT)
Output Low Voltage
VOL
ISINK = 3mA
0.4
V
I2C TIMING CHARACTERISTICS
I2C Write Address
AE
Hex
I2C Read Address
AF
Hex
SCL Clock Frequency
fSCL
Bus Free Time Between
STOP and START
Condition
tBUF
1.3
µs
tHD,STA
0.6
µs
SCL Pulse-Width Low
tLOW
1.3
µs
SCL Pulse-Width High
tHIGH
0.6
µs
Setup Time for a
Repeated START
Condition
tSU,STA
0.6
µs
Data Hold Time
tHD;DAT
0
Data Setup Time
tSU;DAT
100
ns
Setup Time for STOP
Condition
tSU;STO
0.6
µs
Hold Time (Repeated)
START Condition
Lower limit not tested
0
400
0.9
kHz
µs
Pulse Width of
Suppressed Spike
tSP
50
ns
Bus Capacitance
Cb
400
pF
SDA and SCL Receiving
Rise Time
Tr
(Note 4)
20
300
ns
SDA and SCL Receiving
Fall Time
tRf
(Note 4)
20 x
VDD/5.5
300
ns
SDA Transmitting Fall
Time
tof
20 x
VDD/5.5
250
ns
Note 1: All devices are 100% production tested at TA = +25°C. Specifications over temperature limits are guaranteed by Maxim
Integrated’s bench or proprietary automated test equipment (ATE) characterization.
Note 2: Specifications are guaranteed by Maxim Integrated’s bench characterization and by 100% production test using proprietary
ATE setup and conditions.
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19-8453
Maxim Integrated | 5
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Note 3: For design guidance only. Not production tested.
Note 4: These specifications are guaranteed by design, characterization, or I2C protocol.
SDA
tSU,STA
tSU,DAT
tLOW
tHD,DAT
tHD,STA
tBUF
tSP
tSU,STO
tHIGH
SCL
tHD,STA
tR
tF
START CONDITION
REPEATED START CONDITION
STOP
CONDITION
START
CONDITION
Figure 1. I2C-Compatible Interface Timing Diagram
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19-8453
Maxim Integrated | 6
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Typical Operating Characteristics
(VDD = 1.8V, VLED+ = 5.0V, TA = +25°C, RST, unless otherwise noted.)
RED LED SUPPLY HEADROOM
toc02
60
40
30
ILED = 20mA
10
40
30
ILED = 20mA
20
2
3
4
5
0
1
2
VLED VOLTAGE (V)
50000
0.8
45000
COUNTS (SUM)
0.7
0.6
0.5
0.4
2
25000
20000
RED
2
IR
GREEN
0
1.5
2.5
5
10
DISTANCE (mm)
4
5
15
20
toc06
VDD
2.2V
2.0V
1.8V
1.7V
5.0
4.0
3.0
2.0
1.0
0.0
-50
0
50
100
150
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
VLED SHUTDOWN CURRENT
vs. TEMPERATURE
3
6.0
30000
0
0.14
1
VDD SHUTDOWN CURRENT
vs. TEMPERATURE
7.0
35000
5000
0.0
1
0
VLED VOLTAGE (V)
10000
SHUTDOWN
MODE
0.5
ILED = 20mA
20
5
MODE = LED
SPO2 and HR
ADC RES = 18 BITs
ADC SR = 100 SPS
ADC FULL SCALE = 16384nA
15000
0.3
0
30
toc05
40000
0.1
4
DC COUNTS vs. DISTANCE FOR
WHITE HIGH IMPACT STYRENE CARD
toc04
0.9
0.2
40
VLED VOLTAGE (V)
VDD SUPPLY CURRENT vs
vs..
SUPPLY VOLTAGE
1.0
3
VDD SHUTDOWN CURRENT (µA)
1
50
0
0
0
ILED = 50mA
10
10
0
SUPPLY CURRENT (mA)
VLED = VX_DRV
ILED = 50mA
50
toc03
60
GREEN LED CURRENT (mA)
50
IR LED CURRENT (mA)
RED LED CURRENT (mA)
ILED = 50mA
20
GREEN LED SUPPLY HEADROOM
IR LED SUPPLY HEADROOM
toc01
60
toc07
VLED SHUTDOWN CURRENT (µA)
0.13
0.12
0.11
0.10
VLED = 5.25V
0.09
0.08
VLED = 4.75V
0.07
0.06
-50
0
50
100
150
TEMPERATURE (°C)
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19-8453
Maxim Integrated | 7
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Typical Operating Characteristics (continued)
(VDD = 1.8V, VLED+ = 5.0V, TA = +25°C, RST, unless otherwise noted.)
GREEN LED FORWARD VOLTAGE vs.
FORWARD CURRENT at 25
25°°C
toc15
60
MODE = FLEX LED
ADC RES = 18 BITs
ADC SR = 200 SPS
ADC FULL SCALE = 2048nA
FORWARD CURRENT (mA)
50
40
30
20
10
0
2.7
2.8
2.9
3
3.1
FORWARD VOLTAGE (V)
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Maxim Integrated | 8
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Typical Operating Characteristics (continued)
(VDD = 1.8V, VLED+ = 5.0V, TA = +25°C, RST, unless otherwise noted.)
Pin Configuration
N.C.
1
14
N.C.
SCL
2
13
INT
SDA
3
12
GND
PGND
4
11
VDD
N.C.
5
10
VLED+
N.C.
6
9
VLED+
N.C.
7
8
N.C.
SENSOR
MAX30101
LED
Pin Description
PIN
NAME
FUNCTION
1, 5, 6, 7, 8,
14
N.C.
No Connection. Connect to PCB pad for mechanical stability.
2
SCL
I2C Clock Input
3
SDA
I2C Clock Data, Bidirectional (Open-Drain)
4
PGND
Power Ground of the LED Driver Blocks
9, 10
VLED+
LED Power Supply (anode connection). Use a bypass capacitor to PGND for best performance.
11
VDD
Analog Power Supply Input. Use a bypass capacitor to GND for best performance.
12
GND
Analog Ground
13
INT
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Active-Low Interrupt (Open-Drain). Connect to an external voltage with a pullup resistor.
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Maxim Integrated | 9
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Functional Diagrams
VDD
VLED+
RED
IR
AMBIENT LIGHT
CANCELLATION
GREEN
ANALOG
VISIBLE+IR
ADC
660nm
880nm
527nm
DIE TEMP
DIGITAL
DIGITAL
FILTER
SCL
DATA
REGISTER
I2 C
COMMUNICATION
SDA
INT
ADC
OSCILLATOR
LED DRIVERS
MAX30101
N.C.
N.C.
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N.C.
GND
PGND
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Maxim Integrated | 10
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Detailed Description
The MAX30101 is a complete pulse oximetry and heart- rate sensor system solution module designed for the demanding
requirements of wearable devices. The MAX30101 maintains a very small solution size without sacrificing optical or
electrical performance. Minimal external hardware components are required for integra- tion into a wearable system.
The MAX30101 is fully adjustable through software regis- ters, and the digital output data can be stored in a 32-deep
FIFO within the IC. The FIFO allows the MAX30101 to be connected to a microcontroller or processor on a shared bus,
where the data is not being read continuously from the MAX30101’s registers.
SpO2 Subsystem
The SpO2 subsystem contains ambient light cancellation (ALC), a continuous-time sigma-delta ADC, and propri- etary
discrete time filter. The ALC has an internal Track/ Hold circuit to cancel ambient light and increase the effec- tive dynamic
range. The SpO2 ADC has a programmable full-scale ranges from 2µA to 16µA. The ALC can cancel up to 200µA of
ambient current.
The internal ADC is a continuous time oversampling sigma-delta converter with 18-bit resolution. The ADC sampling rate
is 10.24MHz. The ADC output data rate can be programmed from 50sps (samples per second) to 3200sps.
Temperature Sensor
The MAX30101 has an on-chip temperature sensor for calibrating the temperature dependence of the SpO2 subsystem.
The temperature sensor has an inherent resolution 0.0625°C.
The device output data is relatively insensitive to the wavelength of the IR LED, where the red LED’s wave- length is
critical to correct interpretation of the data. An SpO2 algorithm used with the MAX30101 output signal can compensate
for the associated SpO2 error with ambient temperature changes.
LED Driver
The MAX30101 integrates red, green, and IR LED drivers to modulate LED pulses for SpO2 and HR measurements. The
LED current can be programmed from 0 to 50mA with proper supply voltage. The LED pulse width can be programmed
from 69µs to 411µs to allow the algorithm to optimize SpO2 and HR accuracy and power consumption
based on use cases.
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19-8453
Maxim Integrated | 11
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Register Maps and Descriptions
REGISTER
B7
B6
B5
PPG_
RDY
ALC_
OVF
B4
B3 B2
B1
B0
REG
ADDR
POR
STATE
R/
W
PWR_
RDY
0x00
0X00
R
0x00
R
0x02
0X00
R/
W
0x03
0x00
R/
W
STATUS
Interrupt Status 1
A_FULL
Interrupt Status 2
Interrupt Enable 1
DIE_TEMP
_RDY
A_FULL_
EN
PPG_
RDY_EN
ALC_
OVF_EN
Interrupt Enable 2
DIE_TEMP
_RDY_EN
0x01
FIFO
FIFO Write Pointer
FIFO_WR_PTR[4:0]
0x04
0x00
R/
W
Overflow
Counter
OVF_COUNTER[4:0]
0x05
0x00
R/
W
FIFO Read Pointer
FIFO_RD_PTR[4:0]
0x06
0x00
R/
W
0x07
0x00
R/
W
0x00
R/
W
0x09
0x00
R/
W
0x0A
0x00
R/
W
0x0B
0x00
R/
W
LED1_PA[7:0]
0x0C
0x00
R/
W
LED2_PA[7:0]
0x0D
0x00
R/
W
LED3_PA[7:0]
0x0E
0x00
R/
W
LED4_PA[7:0]
0x0F
0x00
R/
W
FIFO Data Register
FIFO_DATA[7:0]
CONFIGURATION
FIFO
Configuration
SMP_AVE[2:0]
Mode
Configuration
SHDN
SpO2
Configuration
0
SPO2_ADC_RGE
(Reserved) [1:0]
FIFO_ ROLL
OVER_EN
RESET
FIFO_A_FULL[3:0]
0x08
MODE[2:0]
SPO2_SR[2:0]
LED_PW[1:0]
RESERVED
LED Pulse
Amplitude
Multi-LED Mode
Control Registers
SLOT2[2:0]
SLOT1[2:0]
0x11
0x00
R/
W
SLOT4[2:0]
SLOT3[2:0]
0x12
0x00
R/
W
RESERVED
0x13–
0x17
0xFF
R/
W
RESERVED
0x180x1E
0x00
R
DIE TEMPERATURE
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19-8453
Maxim Integrated | 12
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
REGISTER
B7
Die Temp Integer
B6
B5
B4
B3 B2
B1
B0
TINT[7:0]
Die Temp Fraction
TFRAC[3:0]
Die Temperature
Config
TEMP
_EN
RESERVED
REG
ADDR
POR
STATE
R/
W
0x1F
0x00
R
0x20
0x00
R
0x00
R/
W
0x22–
0x2F
0x00
R/
W
0x21
PART ID
Revision ID
REV_ID[7:0]
0xFE
0xXX*
R
Part ID
PART_ID[7]
0xFF
0x15
R
*XX denotes a 2-digit hexadecimal number (00 to FF) for part revision identification. Contact Maxim Integrated for the
revision ID number assigned for your product.
Interrupt Status (0x00–0x01)
REGISTER
B7
B6
B5
Interrupt Status
1
A_FULL
PPG_RDY
ALC_OVF
B4 B3 B2
Interrupt Status
2
B1
DIE_
TEMP_RDY
B0
REG
ADDR
POR
STATE
R/
W
PWR_
RDY
0x00
0X00
R
0x01
0x00
R
Whenever an interrupt is triggered, the MAX30101 pulls the active-low interrupt pin into its low state until the interrupt is
cleared.
A_FULL: FIFO Almost Full Flag
In SpO2 and HR modes, this interrupt triggers when the FIFO write pointer has a certain number of free spaces
remaining. The trigger number can be set by the FIFO_A_FULL[3:0] register. The interrupt is cleared by reading the
Interrupt Status 1 register (0x00).
PPG_RDY: New FIFO Data Ready
In SpO2 and HR modes, this interrupt triggers when there is a new sample in the data FIFO. The interrupt is cleared by
reading the Interrupt Status 1 register (0x00), or by reading the FIFO_DATA register.
ALC_OVF: Ambient Light Cancellation Overflow
This interrupt triggers when the ambient light cancellation function of the SpO2/HR photodiode has reached its maximum
limit, and therefore, ambient light is affecting the output of the ADC. The interrupt is cleared by reading the Interrupt
Status 1 register (0x00).
PWR_RDY: Power Ready Flag
On power-up or after a brownout condition, when the supply voltage VDD transitions from below the undervoltage lockout
(UVLO) voltage to above the UVLO voltage, a power-ready interrupt is triggered to signal that the module is powered-up
and ready to collect data.
DIE_TEMP_RDY: Internal Temperature Ready Flag
When an internal die temperature conversion is finished, this interrupt is triggered so the processor can read the
temperature data registers. The interrupt is cleared by reading either the Interrupt Status 2 register (0x01) or the TFRAC
register (0x20).
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The interrupts are cleared whenever the interrupt status register is read, or when the register that triggered the interrupt
is read. For example, if the SpO2 sensor triggers an interrupt due to finishing a conversion, reading either the FIFO data
register or the interrupt register clears the interrupt pin (which returns to its normal HIGH state). This also clears all the
bits in the interrupt status register to zero.
Interrupt Enable (0x02-0x03)
REGISTER
B7
B6
B5
B4 B3 B2
Interrupt
Enable 1
A_ FULL_
EN
PPG_
RDY_EN
ALC_
OVF_EN
Interrupt
Enable 2
B1
B0
DIE_TEMP_
RDY_EN
REG
ADDR
POR
STATE
R/
W
0x02
0X00
R/
W
0x03
0x00
R/
W
Each source of hardware interrupt, with the exception of power ready, can be disabled in a software register within the
MAX30101 IC. The power-ready interrupt cannot be disabled because the digital state of the module is reset upon a
brownout condition (low power supply voltage), and the default condition is that all the interrupts are disabled. Also, it is
important for the system to know that a brownout condition has occurred, and the data within the module is reset as a
result.
The unused bits should always be set to zero for normal operation.
FIFO (0x04–0x07)
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
REG ADDR
POR STATE
R/W
FIFO Write Pointer
FIFO_WR_PTR[4:0]
0x04
0x00
R/W
Over Flow Counter
OVF_COUNTER[4:0]
0x05
0x00
R/W
FIFO_RD_PTR[4:0]
0x06
0x00
R/W
0x07
0x00
R/W
FIFO Read Pointer
FIFO Data Register
FIFO_DATA[7:0]
FIFO Write Pointer
The FIFO Write Pointer points to the location where the MAX30101 writes the next sample. This pointer advances for
each sample pushed on to the FIFO. It can also be changed through the I2C interface when MODE[2:0] is 010, 011, or
111.
FIFO Overflow Counter
When the FIFO is full, samples are not pushed on to the FIFO, samples are lost. OVF_COUNTER counts the number of
samples lost. It saturates at 0x1F. When a complete sample is “popped” (i.e., removal of old FIFO data and shifting the
samples down) from the FIFO (when the read pointer advances), OVF_COUNTER is reset to zero.
FIFO Read Pointer
The FIFO Read Pointer points to the location from where the processor gets the next sample from the FIFO through the
I2C interface. This advances each time a sample is popped from the FIFO. The processor can also write to this pointer
after reading the samples to allow rereading samples from the FIFO if there is a data communication error.
FIFO Data Register
The circular FIFO depth is 32 and can hold up to 32 samples of data. The sample size depends on the number of LED
channels (a.k.a. channels) configured as active. As each channel signal is stored as a 3-byte data signal, the FIFO width
can be 3 bytes, 6 bytes, 9 bytes, or 12 bytes in size. The FIFO_DATA register in the I2C register map points to the
next sample to be read from the FIFO. FIFO_RD_PTR points to this sample. Reading FIFO_DATA register, does not
automatically increment the I2C register address. Burst reading this register, reads the same address over and over.
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Each sample is 3 bytes of data per channel (i.e., 3 bytes for RED, 3 bytes for IR, etc.). The FIFO registers (0x04–0x07)
can all be written and read, but in practice only the FIFO_RD_PTR register should be written to in operation. The others
are automatically incremented or filled with data by the MAX30101. When starting a new SpO2 or heart rate conversion, it
is recommended to first clear the FIFO_WR_PTR, OVF_COUNTER, and FIFO_RD_PTR registers to all zeroes (0x00) to
ensure the FIFO is empty and in a known state. When reading the MAX30101 registers in one burst-read I2C transaction,
the register address pointer typically increments so that the next byte of data sent is from the next register, etc. The
exception to this is the FIFO data register, register 0x07. When reading this register, the address pointer does not
increment, but the FIFO_RD_PTR does. So the next byte of data sent represents the next byte of data available in the
FIFO.
Reading from the FIFO
Normally, reading registers from the I2C interface autoincrements the register address pointer, so that all the registers
can be read in a burst read without an I2C start event. In the MAX30101, this holds true for all registers except for the
FIFO_DATA register (register 0x07). Reading the FIFO_DATA register does not automatically increment the register
address. Burst reading this register reads data from the same address over and over. Each sample comprises multiple
bytes of data, so multiple bytes should be read from this register (in the same transaction) to get one full sample. The
other exception is 0xFF. Reading more bytes after the 0xFF register does not advance the address pointer back to 0x00,
and the data read is not meaningful.
FIFO Data Structure
The data FIFO consists of a 32-sample memory bank that can store GREEN, IR, and RED ADC data. Since each sample
consists of three channels of data, there are 9 bytes of data for each sample, and therefore 288 total bytes of data can
be stored in the FIFO.
The FIFO data is left-justified, as shown in Table 1; in other words, the MSB bit is always in the bit 17 data position,
regardless of ADC resolution setting. See Table 2 for a visual presentation of the FIFO data structure.
FIFO_DATA[0]
FIFO_DATA[1]
FIFO_DATA[2]
FIFO_DATA[3]
FIFO_DATA[4]
FIFO_DATA[5]
FIFO_DATA[6]
FIFO_DATA[7]
FIFO_DATA[8]
FIFO_DATA[9]
FIFO_DATA[10]
FIFO_DATA[11]
…
FIFO_DATA[12]
Resolution
FIFO_DATA[16]
ADC
FIFO_DATA[17]
Table 1. FIFO Data is Left-Justified
18-bit
17-bit
16-bit
15-bit
FIFO Data Contains 3 Bytes per Channel
The FIFO data is left-justified, meaning that the MSB is always in the same location regardless of the ADC resolution
setting. FIFO DATA[18] – [23] are not used. Table 2 shows the structure of each triplet of bytes (containing the 18-bit
ADC data output of each channel). Each data sample in SpO2 mode comprises two data triplets (3 bytes each), To read
one sample, requires an I2C read command for each byte. Thus, to read one sample in SpO2 mode, requires 6 I2C byte
reads. To read one sample with three LED channels requires 9 I2C byte reads. The FIFO read pointer is automatically
incremented after the first byte of each sample is read.
Write/Read Pointers
Write/Read pointers are used to control the flow of data in the FIFO. The write pointer increments every time a new
sample is added to the FIFO. The read pointer is incremented every time a sample is read from the FIFO. To reread a
sample from the FIFO, decrement its value by one and read the data register again.
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The FIFO write/read pointers should be cleared (back to 0x00) upon entering SpO2 mode or HR mode, so that there is
no old data represented in the FIFO. The pointers are automatically cleared if VDD is power-cycled or VDD drops below
its UVLO voltage.
Table 2. FIFO Data (3 Bytes per Channel)
BYTE 1
FIFO_
DATA[17]
FIFO_
DATA[16]
BYTE 2
FIFO_
DATA[15]
FIFO_
DATA[14]
FIFO_
DATA[13]
FIFO_
DATA[12]
FIFO_
DATA[11]
FIFO_
DATA[10]
FIFO_
DATA[9]
FIFO_
DATA[8]
BYTE 3
FIFO_
DATA[7]
FIFO_
DATA[6]
FIFO_
DATA[5]
FIFO_
DATA[4]
FIFO_
DATA[3]
FIFO_
DATA[2]
FIFO_
DATA[1]
FIFO_
DATA[0]
Sample 2: LED Channel 3
(Byte 1-3)
Sample 2: LED Channel 2
(Byte 1-3)
NEWER
SAMPLES
Sample 2: LED Channel 1
(Byte 1-3)
Sample 2: RED Channel
(Byte 1-3)
Sample 1: LED Channel 3
(Byte 1-3)
Sample 1: IR Channel
(Byte 1-3)
Sample 1: LED Channel 2
(Byte 1-3)
Sample 1: LED Channel 1
(Byte 1-3)
NEWER
SAMPLES
Sample 2: IR Channel
(Byte 1-3)
Sample 1: RED Channel
(Byte 1-3)
OLDER SAMPLES
OLDER SAMPLES
2(a)
2(b)
Figure 2.a and 2b. Graphical Representation of the FIFO Data Register. The left shows three LEDs in multi-LED mode, and the right
shows IR and Red only in SpO2 Mode.
Pseudo-Code Example of Reading Data from FIFO
First transaction:Get the FIFO_WR_PTR:
START;
end device address + write mode Send address of FIFO_WR_PTR;
REPEATED_START;
Send device address + read mode
Read FIFO_WR_PTR;
STOP;
The central processor evaluates the number of samples to be read from the FIFO:
NUM_AVAILABLE_SAMPLES = FIFO_WR_PTR – FIFO_RD_PTR
(Note: pointer wrap around should be taken into account)
NUM_SAMPLES_TO_READ = < less than or equal to NUM_AVAILABLE_SAMPLES >
Second transaction: Read NUM_SAMPLES_TO_READ samples from the FIFO:
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START;
Send device address + write mode
Send address of FIFO_DATA;
REPEATED_START;
Send device address + read mode
for (i = 0; i < NUM_SAMPLES_TO_READ; i++) {
Read FIFO_DATA;
Save LED1[23:16];
Read FIFO_DATA;
Save LED1[15:8];
Read FIFO_DATA;
Save LED1[7:0];
Read FIFO_DATA;
Save LED2[23:16];
Read FIFO_DATA;
Save LED2[15:8];
Read FIFO_DATA;
Save LED2[7:0];
Read FIFO_DATA;
Save LED3[23:16];
Read FIFO_DATA;
Save LED3[15:8];
Read FIFO_DATA;
Save LED3[7:0];
Read FIFO_DATA;
}
STOP;
START;
Send device address + write mode
Send address of FIFO_RD_PTR;
Write FIFO_RD_PTR;
STOP;
Third transaction: Write to FIFO_RD_PTR register. If the second transaction was successful, FIFO_RD_PTR points
to the next sample in the FIFO, and this third transaction is not necessary. Otherwise, the processor updates the
FIFO_RD_PTR appropriately, so that the samples are reread.
FIFO Configuration (0x08)
REGISTER
FIFO
Configuration
B7
B6
B5
SMP_AVE[2:0]
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B4
B3
FIFO_ROL LOVER_EN
B2
B1
B0
FIFO_A_FULL[3:0]
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REG ADDR
POR STATE
R/W
0x08
0x00
R/W
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High-Sensitivity Pulse Oximeter and
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Bits 7:5: Sample Averaging (SMP_AVE)
To reduce the amount of data throughput, adjacent samples (in each individual channel) can be averaged and decimated
on the chip by setting this register.
Table 3. Sample Averaging
SMP_AVE[2:0]
NO. OF SAMPLES AVERAGED PER FIFO SAMPLE
000
1 (no averaging)
001
2
010
4
011
8
100
16
101
32
110
32
111
32
Bit 4: FIFO Rolls on Full (FIFO_ROLLOVER_EN)
This bit controls the behavior of the FIFO when the FIFO becomes completely filled with data. If FIFO_ROLLOVER_EN
is set (1), the FIFO Address rolls over to zero and the FIFO continues to fill with new data. If the bit is not set (0), then the
FIFO is not updated until FIFO_DATA is read or the WRITE/READ pointer positions are changed.
Bits 3:0: FIFO Almost Full Value (FIFO_A_FULL)
This register sets the number of data samples (3 bytes/sample) remaining in the FIFO when the interrupt is issued. For
example, if this field is set to 0x0, the interrupt is issued when there is 0 data samples remaining in the FIFO (all 32
FIFO words have unread data). Furthermore, if this field is set to 0xF, the interrupt is issued when 15 data samples are
remaining in the FIFO (17 FIFO data samples have unread data).
FIFO_A_FULL[3:0]
EMPTY DATA SAMPLES IN FIFO WHEN
INTERRUPT IS ISSUED
UNREAD DATA SAMPLES IN FIFO WHEN
INTERRUPT IS ISSUED
0x0h
0
32
0x1h
1
31
0x2h
2
30
0x3h
3
29
…
…
...
0xFh
15
17
Mode Configuration (0x09)
REGISTER
B7
B6
Mode
Configuration
SHDN
RESET
B5
B4
B3
B2
B1
B0
MODE[2:0]
REG ADDR
POR STATE
R/W
0x09
0x00
R/W
Bit 7: Shutdown Control (SHDN)
The part can be put into a power-save mode by setting this bit to one. While in power-save mode, all registers retain their
values, and write/read operations function as normal. All interrupts are cleared to zero in this mode.
Bit 6: Reset Control (RESET)
When the RESET bit is set to one, all configuration, threshold, and data registers are reset to their power-on-state through
a power-on reset. The RESET bit is cleared automatically back to zero after the reset sequence is completed. Note:
Setting the RESET bit does not trigger a PWR_RDY interrupt event.
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Bits 2:0: Mode Control
These bits set the operating state of the MAX30101. Changing modes does not change any other setting, nor does it
erase any previously stored data inside the data registers.
Table 4. Mode Control
MODE[2:0]
MODE
ACTIVE LED CHANNELS
000
Do not use
001
Do not use
010
Heart Rate mode
011
SpO2 mode
Red only
Red and IR
100–110
Do not use
111
Multi-LED mode
Green, Red, and/or IR
SpO2 Configuration (0x0A)
REGISTER
B7
B6
SpO2
Configuration
B5
B4
SPO2_ADC_RGE[1:0]
B3
B2
SPO2_SR[2:0]
B1
B0
REG ADDR
POR STATE
R/W
0x0A
0x00
R/W
LED_PW[1:0]
Bits 6:5: SpO2 ADC Range Control
This register sets the SpO2 sensor ADC’s full-scale range as shown in Table 5.
Table 5. SpO2 ADC Range Control (18-Bit Resolution)
SPO2_ADC_RGE[1:0]
LSB SIZE (pA)
FULL SCALE (nA)
00
7.81
2048
01
15.63
4096
02
31.25
8192
03
62.5
16384
Bits 4:2: SpO2 Sample Rate Control
These bits define the effective sampling rate with one sample consisting of one IR pulse/conversion, one RED pulse/
conversion, and one GREEN pulse/conversion. The sample rate and pulse-width are related in that the sample rate sets
an upper bound on the pulse-width time. If the user selects a sample rate that is too high for the selected LED_PW
setting, the highest possible sample rate is programmed instead into the register.
Table 6. SpO2 Sample Rate Control
SPO2_SR[2:0]
SAMPLES PER SECOND
000
50
001
100
010
200
011
400
100
800
101
1000
110
1600
111
3200
See Table 15 and Table 16 for Pulse-Width vs. Sample Rate information.
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Bits 1:0: LED Pulse Width Control and ADC Resolution
These bits set the LED pulse width (the IR, Red, and Green have the same pulse width), and, therefore, indirectly sets
the integration time of the ADC in each sample. The ADC resolution is directly related to the integration time.
Table 7. LED Pulse Width Control
LED_PW[1:0]
PULSE WIDTH (µs)
ADC RESOLUTION (bits)
00
69 (68.95)
15
01
118 (117.78)
16
10
215 (215.44)
17
11
411 (410.75)
18
LED Pulse Amplitude (0x0C–0x0F)
REGISTER
B7
B6
B5
LED Pulse Amplitude
B4
B3
B2
B1
B0
REG ADDR
POR STATE
R/W
LED1_PA[7:0]
0x0C
0x00
R/W
LED2_PA[7:0]
0x0D
0x00
R/W
LED3_PA[7:0]
0x0E
0x00
R/W
LED4_PA[7:0]
0x0F
0x00
R/W
These bits set the current level of each LED as shown in Table 8
Table 8. LED Current Control
LEDx_PA [7:0]
TYPICAL LED CURRENT (mA)*
0x00h
0.0
0x01h
0.2
0x02h
0.4
…
…
0x0Fh
3.0
…
…
0x1Fh
6.2
…
…
0x3Fh
12.6
…
…
0x7Fh
25.4
…
…
0xFFh
51.0
.*Actual measured LED current for each part can vary significantly due to the trimming methodology.
Multi-LED Mode Control Registers (0x11–0x12)
REGISTER
Multi-LED Mode Control Registers
B7
B6
B5
B4
B3
B2
B1
B0
REG ADDR
POR STATE
R/W
SLOT2[2:0]
SLOT1[2:0]
0x11
0x00
R/W
SLOT4[2:0]
SLOT3[2:0]
0x12
0x00
R/W
In multi-LED mode, each sample is split into up to four time slots, SLOT1 through SLOT4. These control registers
determine which LED is active in each time slot, making for a very flexible configuration.
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Table 9. Multi-LED Mode Control Registers
SLOTx[2:0] Setting
WHICH LED IS ACTIVE
LED PULSE AMPLITUDE SETTING
000
None (time slot is disabled)
N/A (Off)
001
LED1 (RED)
LED1_PA[7:0]
010
LED2 (IR)
LED2_PA[7:0]
011*
LED3 (GREEN)
LED3_PA[7:0]
LED4 (GREEN)
LED4_PA[7:0]
100
None
N/A (Off)
101
RESERVED
RESERVED
110
RESERVED
RESERVED
111
RESERVED
RESERVED
Each slot generates a 3-byte output into the FIFO. One sample comprises all active slots, for example if SLOT1 and
SLOT2 are non-zero, then one sample is 2 x 3 = 6 bytes. If SLOT1 through SLOT3 are all non-zero, then one sample is 3
x 3 = 9 bytes. The slots should be enabled in order (i.e., SLOT1 should not be disabled if SLOT2 or SLOT3 are enabled).
*Both LED3 and LED4 are wired to Green LED. Green LED sinks current out of LED3_PA[7:0] and LED4_PA[7:0]
configurationin Multi-LED Mode and SLOTx[2:0] = 011.
Temperature Data (0x1F–0x21)
REGISTER
B7
B6
B5
B4
Temp_Integer
B3
B2
B1
B0
TINT[7]
Temp_Fraction
TFRAC[3:0]
Die Temperature
Config
TEMP_EN
REG ADDR
POR STATE
R/W
0x1F
0x00
R/W
0x20
0x00
R/W
0x21
0x00
R/W
Temperature Integer
The on-board temperature ADC output is split into two registers, one to store the integer temperature and one to store
the fraction. Both should be read when reading the temperature data, and the equation below shows how to add the two
registers together:
TMEASURED = TINTEGER + TFRACTION
This register stores the integer temperature data in 2’s complement format, where each bit corresponds to 1°C.
Table 10. Temperature Integer
REGISTER VALUE (hex)
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TEMPERATURE (°C)
0x00
0
0x00
+1
...
...
0x7E
+126
0x7F
+127
0x80
-128
0x81
-127
...
...
0xFE
-2
0xFF
-1
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Temperature Fraction
This register stores the fractional temperature data in increments of 0.0625°C. If this fractional temperature is paired with
a negative integer, it still adds as a positive fractional value (e.g., -128°C + 0.5°C = -127.5°C).
Temperature Enable (TEMP_EN)
This is a self-clearing bit which, when set, initiates a single temperature reading from the temperature sensor. This bit
clears automatically back to zero at the conclusion of the temperature reading when the bit is set to one.
Timing for Measurements and Data Collection
Slot Timing in Multi-LED Modes
The MAX30101 can support up to three LED channels of sequential processing (Red, IR, and Green). In multi-LED
modes, a time slot or period exists between active sequential channels. Table 11 displays the four possible channel slot
times associated with each pulse width setting. [[Figure 3. Channel Slot Timing for the SpO2 Mode with a 1kHz Sample
Rate]] shows an example of channel slot timing for a SpO2 mode application with a 1kHz sample rate.
Table 11. Slot Timing
PULSE-WIDTH SETTING (µs)
CHANNEL SLOT TIMING (TIMING
PERIOD BETWEEN PULSES) (µs)
CHANNEL-CHANNEL TIMING
(RISING EDGE-TO-RISING EDGE) (µs)
69
358
427
118
407
525
215
505
720
411
696
1107
Red On
69μs
Red Off
931μs
RED LED
660nm
IR On
69μs
IR Off
931μs
358μs
INFRARED LED
880nm
Figure 3. Channel Slot Timing for the SpO2 Mode with a 1kHz Sample Rate
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Timing in SpO2 Mode
The internal FIFO stores up to 32 samples, so that the system processor does not need to read the data after every
sample. SpO2 can be calibrated using temperature
data. In this case, the temperature does not need to be sampled very often – once a second or every few seconds should
be sufficient.
15ms TO 300ms
SAMPLE #1
LED
OUTPUTS
RED
SAMPLE #2
IR
RED
IR
SAMPLE #3
RED
IR
SAMPLE #16 SAMPLE #17
~
RED
IR
RED
IR
RED
IR
RED
IR
~
INT
29ms
TEMP
SENSOR
TEMPERATURE SAMPLE
I2C BUS
~
1
2
3
4
5
6
Figure 4. Timing for Data Acquisition and Communication When in SpO2 Mode
Table 12. Events Sequence for Figure 4 in SpO2 Mode
EVENT
DESCRIPTION
1
Enter into SpO2 Mode. Initiate
a Temperature measurement.
I2C Write Command sets MODE[2:0] = 0x03 and set A_FULL_EN. Then, to enable and
initiate a single temperature measurement, set TEMP_EN and DIE_TEMP_RDY_EN.
2
Temperature Measurement
Complete, Interrupt
Generated
DIE_TEMP_RDY interrupt triggers, alerting the central processor to read the data.
3
Temp Data is Read, Interrupt
Cleared
4
FIFO is Almost Full, Interrupt
Generated
5
FIFO Data is Read, Interrupt
Cleared
6
Next Sample is Stored
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COMMENTS
Interrupt is generated when the FIFO almost full threshold is reached.
New Sample is stored at the new read pointer location. Effectively, it is now the first
sample in the FIFO.
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Timing in HR Mode
The internal FIFO stores up to 32 samples, so that the system processor does not need to read the data after every
sample. In HR mode (Figure 5), unlike in SpO2 mode, temperature information is not necessary to interpret the data. The
user can select either the Red, IR, or Green LED channel for heart rate.
15ms TO 300ms
LED
OUTPUTS
SAMPLE #1
SAMPLE #2
SAMPLE #3
IR
IR
IR
SAMPLE #30
SAMPLE #31
IR
IR
~
INT
~
I2C Bus
~
1
2
IR
3
IR
4
Figure 5. Timing for Data Acquisition and Communication When in HR Mode
Table 13. Events Sequence for Figure 5 in HR Mode
EVENT
DESCRIPTION
COMMENTS
1
Enter into Mode
I2C Write Command sets MODE[2:0] = 0x02. Mask the A_FULL_EN
Interrupt.
2
FIFO is Almost Full, Interrupt
Generated
Interrupt is generated when the FIFO has only one empty space left.
3
FIFO Data is Read, Interrupt
Cleared
4
Next Sample is Stored
New sample is stored at the new read pointer location. Effectively, it is now the first
sample in the FIFO.
Power Sequencing and Requirements
Power-Up Sequencing
Figure 6 shows the recommended power-up sequence for the MAX30101. It is recommended to power the VDD supply
first, before the LED power supplies (VLED+). The interrupt and I2C pins can be pulled up to an external voltage even
when the power supplies are not powered up. After the power is established, an interrupt occurs to alert the system that
the MAX30101 is ready for operation. Reading the I2C interrupt register clears the interrupt, as shown in the Figure 6.
Power-Down Sequencing
The MAX30101 is designed to be tolerant of any power supply sequencing on power-down.
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MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
I2C Interface
The MAX30101 features an I2C/SMBus-compatible, 2-wire serial interface consisting of a serial data line (SDA) and a
serial clock line (SCL). SDA and SCL facilitate communication between the MAX30101 and the master at clock rates up
to 400kHz. Figure 1 shows the 2-wire interface timing diagram. The master generates SCL and initiates data transfer on
the bus. The master device writes data to the MAX30101 by transmitting the proper slave address followed by data. Each
transmit sequence is framed by a START (S) or REPEATED START (Sr) condition and a STOP (P) condition. Each word
transmitted to the MAX30101 is 8 bits long and is followed by an acknowledge clock pulse. A master reading data from
the MAX30101 transmits the proper slave address followed by a series of nine SCL pulses.
The MAX30101 transmits data on SDA in sync with the master-generated SCL pulses. The master acknowledges receipt
of each byte of data. Each read sequence is framed by a START (S) or REPEATED START (Sr) condition, a not
acknowledge, and a STOP (P) condition. SDA operates as both an input and an open-drain output. A pullup resistor,
typically greater than 500Ω, is required on SDA. SCL operates only as an input. A pullup resistor, typically greater than
500Ω, is required on SCL if there are multiple masters on the bus, or if the single master has an open-drain SCL output.
Series resistors in line with SDA and SCL are optional. Series resistors protect the digital inputs of the MAX30101 from
high voltage spikes on the bus lines and minimize crosstalk and undershoot of the bus signals.
VDD
VLED+
PWR_RDY INTERRUPT
INT
HIGH (I/O PULLUP )
SDA, SCL
HIGH (I/O PULLUP )
READ TO CLEAR
INTERRUPT
Figure 6. Power-Up Sequence of the Power Supply Rails
Bit Transfer
One data bit is transferred during each SCL cycle. The data on SDA must remain stable during the high period of the
SCL pulse. Changes in SDA while SCL is high are control signals. See the START and STOP Conditions section.
START and STOP Conditions
SDA and SCL idle high when the bus is not in use. A master initiates communication by issuing a START condition.
A START condition is a high-to-low transition on SDA with SCL high. A STOP condition is a low-to-high transition on
SDA while SCL is high (Figure 7). A START condition from the master signals the beginning of a transmission to the
MAX30101. The master terminates transmission, and frees the bus, by issuing a STOP condition. The bus remains active
if a REPEATED START condition is generated instead of a STOP condition.
Early STOP Conditions
The MAX30101 recognizes a STOP condition at any point during data transmission except if the STOP condition occurs
in the same high pulse as a START condition. For proper operation, do not send a STOP condition during the same SCL
high pulse as the START condition.
Slave Address
A bus master initiates communication with a slave device by issuing a START condition followed by the 7-bit slave ID.
When idle, the MAX30101 waits for a START condition followed by its slave ID. The serial interface compares each
slave ID bit by bit, allowing the interface to power down and disconnect from SCL immediately if an incorrect slave ID is
detected. After recognizing a START condition followed by the correct slave ID, the MAX30101 is programmed to accept
or send data. The LSB of the slave ID word is the read/write (R/W) bit. R/W indicates whether the master is writing to or
reading data from the MAX30101 (R/W = 0 selects a write condition, R/W = 1 selects a read condition). After receiving
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MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
the proper slave ID, the MAX30101 issues an ACK by pulling SDA low for one clock cycle.
The MAX30101 slave ID consists of seven fixed bits, B7–B1 (set to 0b1010111). The most significant slave ID bit (B7) is
transmitted first, followed by the remaining bits. Table 14 shows the possible slave IDs of the device.
Acknowledge
The acknowledge bit (ACK) is a clocked 9th bit that the MAX30101 uses to handshake receipt each byte of data when in
write mode (Figure 8). The MAX30101 pulls down SDA during the entire master-generated 9th clock pulse if the previous
byte is successfully received. Monitoring ACK allows for detection of unsuccessful data transfers. An unsuccessful data
transfer occurs if a receiving device is busy or if a system fault has occurred. In the event of an unsuccessful data
transfer, the bus master retries communication. The master pulls down SDA during the 9th clock cycle to acknowledge
receipt of data when the MAX30101 is in read mode. An acknowledge is sent by the master after each read byte to allow
data transfer to continue. A not-acknowledge is sent when the master reads the final byte of data from the MAX30101,
followed by a STOP condition.
Write Data Format
For the write operation, send the slave ID as the first byte followed by the register address byte and then one or more
data bytes. The register address pointer increments automatically after each byte of data received, so for example the
entire register bank can be written by at one time. Terminate the data transfer with a STOP condition. The write operation
is shown in Figure 9.
The internal register address pointer increments automatically, so writing additional data bytes fill the data registers in
order.
Table 14. Slave ID Description
B7
B6
B5
B4
B3
B2
B1
B0
WRITE ADDRESS
READ ADDRESS
1
0
1
0
1
1
1
RW
0xAE
0xAF
S
Sr
P
SCL1
SDA1
Figure 7. START, STOP, and REPEATED START Conditions
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MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
CLOCK PULSE FOR
ACKNOWLEDGMENT
START
CONDITION
1
SCL1
2
8
9
NOT ACKNOWLEDGE
SDA1
ACKNOWLEDGE
Figure 8. Acknowledge
S
1
0
1
0
1
1
1
R/W
=0
ACK
A7
SLAVE ID
D7
D6
D5
D4
D3
A6
A5
A4
A3
A2
A1
A0
ACK
REGISTER ADDRESS
D2
D1
D0
ACK
P
DATA BYTE
S = START CONDITION
P = STOP CONDITION
ACK = ACKNOWLEDGE BY THE RECEIVER
INTERNAL ADDRESS POINTER AUTO -INCREMENT (FOR WRITING MULTIPLE BYTES
Figure 9. Writing One Data Byte to the MAX30101
Read Data Format
For the read operation, two I2C operations must be performed. First, the slave ID byte is sent followed by the I2C register
that you wish to read. Then a REPEAT START (Sr) condition is sent, followed by the read slave ID. The MAX30101 then
begins sending data beginning with the register selected in the first operation. The read pointer increments automatically,
so the MAX30101 continues sending data from additional registers in sequential order until a STOP (P) condition is
received. The exception to this is the FIFO_DATA register, at which the read pointer no longer increments when reading
additional bytes. To read the next register after FIFO_DATA, an I2C write command is necessary to change the location
of the read pointer. Figure 10 show the process of reading one byte or multiple bytes of data. An initial write operation is
required to send the read register address.
Data is sent from registers in sequential order, starting from the register selected in the initial I2C write operation. If the
FIFO_DATA register is read, the read pointer will not automatically increment, and subsequent bytes of data will contain
the contents of the FIFO.
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MAX30101
S
1
0
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
1
0
1
1
1
R/W
=0
ACK
A7
A6
A5
SLAVE ID
Sr
1
0
1
0
1
A4
A3
A2
A1
A0
ACK
D2
D1
D0
NACK
A2
A1
A0
ACK
D2
D1
D0
AM
D2
D1
D0
NACK
REGISTER ADDRESS
1
1
R/W
=1
ACK
D7
D6
D5
SLAVE ID
D4
D3
P
DATA BYTE
S = START CONDITION
Sr = REPEATED START CONDITION
P = STOP CONDITION
ACK = ACKNOWLEDGE BY THE RECEIVER
NACK = NOT ACKNOWLEDGE
Figure 10. Reading one byte of data from MAX30101
S
1
0
1
0
1
1
1
R/W
=0
ACK
A7
A6
A5
SLAVE ID
Sr
1
0
1
0
1
D6
D5
D4
D3
A3
REGISTER ADDRESS
1
1
R/W
=1
ACK
D7
D6
D5
SLAVE ID
D7
A4
D4
D3
DATA 1
D2
D1
D0
AM
D7
DATA n-1
S = START CONDITION
Sr = REPEATED START CONDITION
P = STOP CONDITION
D6
D5
D4
D3
P
DATA n
ACK = ACKNOWLEDGE BY THE RECEIVER
AM = ACKNOWLEDGE BY THE MASTER
NACK = NOT ACKNOWLEDGE
Figure 11. Reading multiple bytes of data from the MAX30101
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Maxim Integrated | 28
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Applications Information
Soldering and Cleaning Recommendations
The MAX30101 comes in an OLGA package that is not sealed from dust or liquid. Because of this, the MAX30101
requires special care to install on a board.
If possible, the MAX30101 should be the last component installed on the board. Install the MAX30101 after the
board ultrasonic cleaning is completed. When soldering the MAX30101, use a low-residue, no-clean solder paste. The
MAX30101 should not be cleaned with a liquid solution, baked, or coated with anything.
The Application Note 6381 serves as a guide for handling the OLGA package when manufacturing a board.
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 SpO2 and HR Modes are summarized in the Table 15 and Table 16:
Power Considerations
The LED waveforms and their implication for power supply design are discussed in this section.
The LEDs in the MAX30101 are pulsed with a low duty cycle for power savings, and the pulsed currents can cause ripples
in the VLED+ 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 15. SpO2 Mode (Allowed Settings)
SAMPLES PER SECOND
PULSE WIDTH (µs)
69
118
215
411
50
O
O
O
O
100
O
O
O
O
200
O
O
O
O
400
O
O
O
O
800
O
O
O
1000
O
O
1600
O
3200
Resolution (bits)
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Maxim Integrated | 29
MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Table 16. HR Mode (Allowed Settings)
PULSE WIDTH (µs)
SAMPLES PER SECOND
69
118
215
411
50
O
O
O
O
100
O
O
O
O
200
O
O
O
O
400
O
O
O
O
800
O
O
O
O
1000
O
O
O
O
1600
O
O
O
16
17
3200
O
Resolution (bits)
15
18
SpO2 Temperature Compensation
The MAX30101 has an accurate on-board temperature sensor that digitizes the IC’s internal temperature upon command
from the I2C master. The temperature has an effect on the wavelength of the red and IR LEDs. While the device output
data is relatively insensitive to the wavelength of the IR LED, the red LED’s wavelength is critical to correct interpretation
of the data.
Table 17 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 17 to estimate the temperature.
Table 17. RED LED Current Settings vs. LED Temperature Rise
RED LED
CURRENT
SETTING
RED LED DUTY CYCLE (% OF LED PULSEWIDTH TO SAMPLE TIME)
ESTIMATED TEMPERATURE RISE (ADD TO TEMP
SENSOR MEASUREMENT) (°C)
00000001 (0.2mA)
8
0.1
11111010 (50mA)
8
2
00000001 (0.2mA)
16
0.3
11111010 (50mA)
16
4
00000001 (0.2mA)
32
0.6
11111010 (50mA)
32
8
Red LED Current Settings vs. LED Temperature Rise
Add this to the module temperature 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.
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MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Typical Application Circuits
+1.8V
20mA
+5.0V
200mA MAX
0.1µF
10µF
4.7µF
VLED+
0.1µF
VDD
1kΩ
RED
IR
AMBIENT LIGHT
CANCELLATION
GREEN
ANALOG
VISIBLE+IR
ADC
660nm
880nm
527nm
DIE TEMP
DIGITAL
DIGITAL
FILTER
VDDIO
SCL
DATA
REGISTER
I2 C
SDA
COMMUNICATION
HOST
PROCESSOR
INT
ADC
OSCILLATOR
LED DRIVERS
MAX30101
N.C.
N.C.
N.C.
GND
PGND
(NOT CONNECTED )
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX30101EFD+T
-40°C to +85°C
14 OESIP
(0.8mm Pin Pitch)
+Denotes lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
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MAX30101
High-Sensitivity Pulse Oximeter and
Heart-Rate Sensor for Wearable Health
Revision History
REVISION
NUMBER
REVISION
DATE
0
3/16
Initial release
6/18
Changed register descriptions, updated tables 8,9,13,15,16, removed Proximity
function, updated FIFO_A_FULL description table
10–15, 18,
21–25, 27, 28
2
9/18
Updated the Applications, Absolute Maximum Ratings, Electrical Characteristics, Pin
Description, and Power-Up Sequencing sections; updated the System Diagram, Pin
Configuration, Functional Diagram, and Typical Application Circuit; updated the
Register Maps and Descriptions, Mode Configuration (0x09), SpO2 Configuration
(0x0A), LED Pulse Amplitude (0x0C–0x0F), Table 8, and Table 9.
1–5, 9–11,19,
21–22, 29, 32
3
6/20
Updated SpO2 Sample Rate Control[2:4] (0x0A) and Applications Information
section
1
PAGES
CHANGED
DESCRIPTION
—
24, 34
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max
limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
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