IEC 60601 Main requirements for the certification of a device with a Li-ion batt

[everq32]

Dear. I need help in the following question:

Dear. I need help in the following question

I work in the development of a wearable device and its main use is to record ECG signals. This is powered by a 3.7V Li-ion battery. This battery is not accessible to the user, but to charge it through a USB port that must be connected to a PC.
The user should not use the device while it is charging the battery. In order to comply with the IEC 60601 standard, I need to clarify if it is necessary to make an isolating barrier in the device. I have read a lot on the subject, but there is no clear answer to answer my question.
Some indicate that it is not necessary to isolate the circuit, but others indicate that yes.
The device is planned to be commercialized in the US market. Based on this data, should I add some isolator to the USB stage?
I appreciate your help on the subject.

 

[Pads38]

The clear and absolute requirement is that your device must not exceed the leakage current figures given in 60601-1 clause 8.7.

As you are measuring ECG you will require type BF or CF applied parts. This can mean currents cannot exceed 10uA DC or 100uA AC in normal conditions. (Type BF - type CF are more strict).

The impedance of your ECG connection could be as little as 1kohm. With 3.7V supply that could cause a current of several millamps (in fault condition).

That needs to be prevented.

Also, it is unlikely that you will be physically preventing the user from connecting to a USB while the ECG wires are still connected - potentially to the user. So the possibility of significant currents from the PC or charger must be considered.

To answer your question - will we need isolation?
Yes.

 

[everq32]

Thanks.
This helps to clarify my doubts. It is best to place the insulation in the USB port.

 

[Pads38]

Some form of isolation is likely to be required for the USB

but, as I stated above, the 3.7V is enough to exceed allowable leakage / auxillary currents so you will need protection there as well.

 

[VinceTech]

Charging the battery is still the normal use of the device. The basic safety is still need to be maintained. This means the USB charger still need to be 2MOOP isolated from mains if the device doesn't provide any MOOP for mains voltage.

There are three options:
1. USB on device is 2MOOP isolated for mains votlage
2. Charging device requirement is provided in the user instruction. for example, 'device has to be charged by USB of an IEC 60950 IT equipment)
3. Provide double insulated USB power supply which provide 2MOOP fo rmains voltage

Hope this is correct. Any comments is appreciated.