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Maxim Integrated MAX17703 Dev Kit Power On Issue

hamza nasir
I have purchased the Maxim Integrated Analog Devices development kit MAX17703. Here is the link to the datasheet: MAX17703EVKITA Datasheet. The kit is designed for 4.2V, but I have changed the kit's output voltage to suit my application. I want to charge multi-cell lithium-ion batteries with two batteries in series. I am using Panasonic NRC 3400mAh 3.7V green batteries (NRC18650B). The kit's datasheet states that the input voltage range is 6.3V to 60V.
In my case, I changed the VOUT to 8.4V by adjusting RTOP and RBOT, choosing 42.2kΩ for RTOP and 7.32kΩ for RBOT. I also changed the battery deep discharge level to 6V by adjusting R4 in the dev kit to 22kΩ. The charger seems to work fine and charges the batteries, but I am encountering a problem: when the input voltage DCIN to the kit is less than or qual to 12.5v and the battery voltage is around 6.5 to 7V or less, the charger will not start until I provide 13.8V or 14V. When I apply a DCIN input greater than 13.5V, the charging kit turns on and starts charging.
If the charging kit's minimum DC input voltage is 6.3V, why does the charger kit not start at 10V or 11V? Additionally, sometimes the charging kit does not stop charging, and the batteries overheat. I simply connect the batteries at the VOUT pin with two batteries in series. Please help me resolve this issue as soon as possible.
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  • 0

    Hello, Regarding the input voltage calculation for the kit power on, your configuration seems appropriate when using a single 4.2V cell. However, with two cells in series, the minimum voltage level should be adjusted accordingly. For reference, please use the formula provided in the MAX17703DEVKIT datasheet on page 26 under "Setting the Input Undervoltage-Lockout Level (EN/UVLO)" This adjustment is necessary for proper protection. Addressing your primary concern, if the kit only initiates at voltages above 14V and causes battery heating, it indicates a potential internal fault. While the kit is operational, the forced start at higher voltages suggests internal damage. It is advisable to either replace the kit to avoid potential burnout issues. Be cautious, as this could be dangerous. Moreover, if the kit's fault detection mechanism is not triggering under these conditions, it implies that the kit's timer is functioning correctly. However, the lack of fault generation in your scenario points towards an internal defect.

  • 0 in reply to Ozan_tasci

    Thanks for the response. Could you please clarify one more thing related to battery temperature? The datasheet for this kit mentions that we can operate it with a battery temperature from 45 to 50c max. I am using 18650 lithium ion  panasonic NRC-18650B cells in my application, which is automotive related. The device is placed in a truck where the atmospheric temperature can exceed 50c, could you please suggest another kit suitable for those conditions? or do you think we can place this kit in such conditions?

  • +1 in reply to hamza nasir

    Hello,
    The data sheet clearly states the temperature range, stating that you cannot exceed these limits. Please be careful, as you are dealing with batteries that can be dangerous at high temperatures.

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