What are the recommendations if I don't use one of the rails in the MAX20360?

And what is the guidance for the external components? If you are not using any rails you can leave the pin and the external components unpopulated.

How do I reduce influence from the temperature of the surrounding environment to MAX30205 when it is used to measure body temperature?

MAX30205 is used to measure body temperature. To reduce the influence of the ambient environment, rubber sheet or plastic can be used to serve as thermal insulation between the device and the environment everywhere except the contact between the point of contact of the thermometer and the object/heat source to be measured. Please refer to the illustration below:

Which thermal glue/paste is recommended for MAX30205 Temperature Sensor?

Our Business Unit recommends Arctic Silver Thermal Adhesive .

App Note AN6502 discusses a large discrepancy between the actual and measured temperature. How can you explain it?

The thermal equilibrium figure below has been taken out of context in this app note. This figure is to explain what happens in the first 10 to 20 seconds after the sensor is placed in contact with the skin and has little to do with steady state accuracy.

How does the MAX30205 sense temperature?

The MAX30205 measures the temperature of its own die. The thermal path between the die and the outside world determines the accuracy of temperature measurements. External temperature is conducted to the die primarily through the leads and the exposed pad. Because of this, the device most easily measures the PCB temperature. For ambient temperature measurements, mount the device on a PCB (or a section of the PCB) that is at ambient temperature. Temperature errors due to self-heating of the device die are minimal due to the low supply current.

How does self-heating of MAX30205 affect measurement?

The power consumption of MAX30205 is very low, and the temperature change resulting from self-heating is less than 0.02 degree. This change is negligible for measurement.

The MAX30205 datasheet states typical Quiescent supply current (Iq) of MAX30205 as 600uA. What is the status of the AFE under this condition?

When Iq is 600uA as stated in the datasheet, I2C is inactive, but AFE is operating. The 1.65uA quiescent current refers to the supply current in shutdown mode, when both the AFE and the I2C are not in operation.

Is there time response data for the MAX30205 mounted on PCB material, and any performance improvement suggestions?

For time response of PCB material the only data taken is for the EVKit PCB. The time response of this PCB is around 15sec. What happens when the PCB is placed next to the skin is that the outer layers of skin (epidermis and dermis) and PCB are at thermal equilibrium in about 30 seconds. During this exchange of heat from the skin to the PCB the skin drops about 1.5 oC. For the PCB to increase its temperature to the temperature of the skin before contact the system is reliant on heat flowing from the blood into the skin and then into the PCB. This is a much slower heat transfer process with a time constant of around 15 to 30 minutes depending on location on the body and difference in the person. It is important for the customer to understand this limitation to be successful in making an accurate and timely temperature sensor. The key design considerations are to maximize the contact area with the skin and minimize the thermal heat capacity of the sensor. (i.e. make the PCB as small as possible or use Flex circuit). The other important consideration is steady state heat loss to the environment which can keep the sensor from ever reaching the initial skin temperature. The thermal resistance to the environment must be much greater than the thermal resistance of the heat flow from the blood through the skin and contact material to the sensor, or the 0.1 oC accuracy will not be realized. Thermal resistance to the environment is best kept high by minimizing copper trace thickness connecting to the MAX30205, and not having ground planes on the PCB. Most heat flow in a PCB is through the copper and all the heat flow in a flex circuit is in the copper.

Possible error on MAX30205EVSYS# datasheet.

Question Description: The datasheet for PN MAX30205 states “Sample period > 10s to eliminate self-heating effects”, i.e. 0.1 samples per second. The user guide for the part’s eval kit, however, states “A minimum of 10sps should be used to avoid self-heating of the sensor”. That large difference and the odd wording of the second statement suggests that it is incorrect. ----------------------------------------------------------------------------------------------------------------------- Answer: The description in MAX30205EVSYS datasheet (Rev. 0) is incorrect, “10sps” refresh rate on page 3 should be "10s" because the refresh rate in the GUI is in second, and "minimum 10s" makes sense here.