Means of Protection Handheld Medical Device Charging and Using at the same time

Hello,

I'm new to the regulations world and have a question about the means of protection for a handheld medical device.

The device contains a 3.8V LiPo battery which can be charged with a USB-C (5V). Now the question has come up about using and charging the device at the same time. Is there any documentation or design guidelines for hardware development that I can consult?

The power management so far includes ESD diodes at the USB connector, the charger IC with integrated fault protection (6.6-V IN overvoltage protection – 1000-mA overcurrent protection), and a battery protection IC for over/under voltage, shorts, etc. There is also the option to add an NTC resistor for battery overheating detection while charging.

Internally in the device, we have 3.3V and 5V for the electronics, and some quite high currents (up to 1.5A).

Thank you for your help!

If the device has things like electrodes or sensors that are in good electrical contact with the skin, it's not advisable to allow the device to be charged and used at the same time. The alternative is to include an isolation barrier between the charging circuits and the patient contact points, but that is normally a large overhead. But anyway, this kind of device needs an expert on the team to make it safe, there's a lot of issues and it wouldn't be something you handle via Q&A on this forum.

If the device only has plastic contact with the patient (user), it's not really a safety issue but it's likely to have trouble complying with IEC 60601-1, especially if you are engaging a third party. The standard has a lot of worst case assumptions that are not really important in this particular case, and in most cases it's no different risk to being able to hold your smart phone while it's charging, with earbuds etc. But it's an uphill battle pushing against them. You probably (again) need someone on the team with a lot of experience in IEC 60601-1 in order to write up all the justifications to confidently overrule the requirements in the standard, and then there is the risk that a third party or regulators might not agree.

Or you can just prohibit charging and use at the same time.

>There is also the option to add an NTC resistor for battery overheating detection while charging.

It's very important that you provide some temperature monitoring during charging as the battery design and certification will only be valid for a specified temperature range as batteries can become unstable if taken outside this range.

Whilst it's not a medical standard, EN 62368-1 Annex M contains lots of requirements on testing rechargeable devices and could be considered to represent "state of the art" in this area.

Hi,
if the device can be used while charging, you must add an isolation of 2MOPP to protect against high leakage currents. usually a Medical Grade DC/DC (not so big, depends of course on the power) or an external MG power supply AC/DC (can be a small wallmount...).
As Charlie wrote, you need to verify there are no unacceptable risk while charging the batteries (overheating , explosion, leakage etc..) during NC and under a SFC.

Are there other external connections to the device?

Avidan

How far are you in the design process? Are there patient connections or something required to use it?
You might consider locating the USB charging port that it gets covered by a required attachment. Be aware of risks, like safe covering, not a flap which might be snapped of by an annoyed user.

Thank you all for the answers

Avidan B said:

Hi,
if the device can be used while charging, you must add an isolation of 2MOPP to protect against high leakage currents. usually a Medical Grade DC/DC (not so big, depends of course on the power) or an external MG power supply AC/DC (can be a small wallmount...).
As Charlie wrote, you need to verify there are no unacceptable risk while charging the batteries (overheating , explosion, leakage etc..) during NC and under a SFC.

Are there other external connections to the device?

Avidan

Click to expand...

To clarify, the handheld device in question doesn't have any electrical contact points. While other parts of the device do come into contact with the patient, they're not electrically connected. The aim is to ensure that users can utilize any standard USB-C cable or wall adapter. This flexibility is crucial since there's a high likelihood that users might misplace the provided medical-grade wall charger or resort to using an alternative one. Therefore, the electronics need to be designed to accommodate this requirement.

For power management, a DC/DC converter would be suitable for meeting the 2MOPP (Means of Patient Protection) standard ?
However, a typical battery charger like the BQ25X series from TI, which employs LDO (Low Drop-Out) regulation for lithium battery charging, may not suffice?

Most battery management ICs indeed utilize LDO regulation. Regarding specifics, the battery in question has a capacity of around 350mAh (a single cell), and it will be charged at a rate of 0.5C, following Li-Po (Lithium Polymer) chemistry standards.