Actions
Forum Thread Details
  • State Verified Answer
  • Replies 10 replies
  • Subscribers 35 subscribers
  • Views 615 views
  • Users 0 members are here
Related

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.
image
imageimage
Parents
  • 0

    C34 looks like a problem waiting to happen it's only rated at 6.3V.  It is worth replacing this but I would be surprised if its causing the problem you describe.

    Can't guess what else is wrong.

    Do be very careful if the batteries get hot - that could be very dangerous.

    Try putting a scope on the output (and maybe other places)  - if the charger is unstable and oscillating it won't work right.

    The data sheet talks about a capacitor across Rbot but I don't see one on your schematic  - there is one on the eval board but it may be the wrong value now.

    MK

  • 0 in reply to michaelkellett

    HI, Thank you for the reply. Firstly, I am having an issue related to the input side. The output capacitor C34, which you highlighted, has a 20% tolerance. I cross-verified this capacitor, and it is not causing the issue. It has 8.4V consistently with no heating issues related to this tantalum capacitor. The issue I am facing is related to the input side. The kit is designed for an input range of 6.3V to 60V, but my kit only starts at 14.2V or greater. This is the problem. I cross-verified everything, and the EN/UVLO IC pin has 2.8V when it turns on. However, below this, the kit does not start. Once the kit starts at 14.2V, it continues to work even if I reduce the voltage to below 14.2V, such as 11V or 10.5V. Initially, we require more voltage to turn on the kit.

  • 0 in reply to hamza nasir

    If you are over-volting a tantalum capacitor then expect a fire !

    It WILL fail. Generally good practice is to use tantalum capacitors at no more than 50% of their voltage rating.

    How do you know that that there is no oscillation on the output side which prevents the 17703 from starting ?

    Does anything at all happen on the output side ?

    Did your board work correctly before you modified it ?

    MK

  • 0 in reply to michaelkellett

    Yes, I actually verified this in two ways. First, I cross verified by connecting an oscilloscope, C34 is not oscillating too much or not even heating. Then, I removed C34 from the kit, as it only provides filtration, and checked again to turn on the kit. However, the same issue persists, so it clearly means the issue is something else.

Reply Children
  • 0 in reply to michaelkellett

    When I connect below 14V, both Flag 1 and Flag 2 show 0V, which means the charger is turned off. ISMON reads 0.1v or lower considered noisy voltages when the charger is off. The charger doesn't respond even if the batteries are completely discharged or their voltages drop below 7.8V. It stays off until I provide 14.2V or higher. when I forcefully turn on the kit with 14.2V input, Flag 2 shows 5.1V and Flag 1 shows 0V, indicating that charging is happening. The battery voltages quickly rise to their maximum of 8.4V. Initially, ISMON reads 1.4V to 1.2V, but then stabilizes around 0.8V or 0.9V, showing a charging current of 6A to 5.33A. Charging continues, and sometimes the batteries start heating when they are deeply discharged. This heating only happens in this specific case. Once the batteries are charged to around 7.4V or 7.8V, they do not heat up.