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BQ28Z610-R1: product safety - short at VC1/VC2

Andre Stelzer
Prodigy 220 points
Part Number: BQ28Z610-R1

Hello,

we do have a product with a bq28z610-r1 for battery protection.

At the moment we do a product-safety test and the following question did appear:

- lets assume a first-error occurs and one of the marked parts (fuel gauge, 100nF at VC1 or 1uF between VC1/VC2) have a short
- this leads to a 5R or 100R or 105R load direct at the battery (or both batteries)
- this load leads to an high current (the resistors are only CH0402 -> 1/16 W) without any protection

So my question is:

How can we maintain safety with a first-error at the fuel gauge, 100nF at VC1 or 1uF between VC1/VC2 (e.g. increase both resistor values)?

best regards
Andre

  • 0
    TI__Guru** 105760 points

    Hello Andre,

    I have never seen this kind of issue before. If you are concerned the capacitor may fail and lead to a closed circuit I would increase the capacitor voltage rating.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 220 points

    Hey Wyatt,

    i also think this case is really really unlikely but unfortunately this is not what product safety looks for. The auditor asks if i can garantuee that the capacitor or the fuelgauge will never ever go into short if a error happend (e.g. production failture of the part, aging effect, ....).

    If yes - all is fine, if no i need additional actions. 

    Unfortunately i dont know any capacitor with a garantuee for "if an error happens, capacitor will aways got to open" and for the fuel gauge there is also no safety hint for VC1/VC2.

    Best regards

    Andre

  • 0 in reply to Andre Stelzer
    TI__Guru** 105760 points

    Hello Andre,

    All of our gauges use a similar recommendation for cell voltage sensing (with capacitor connected between cells) and are used in many industries which require safety precautions.

    If this is a major concern you can place two capacitors in series so if one is damaged the other will prevent an overcurrent condition.

    Is this requirement from a safety certification like UL1642?

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 220 points

    Hello Wyatt,

    our prodcut safety test is based on EN 62368-1.

    The double capacitor can help us for the case "short over capacitor".

    But how can i be sure that the fuel-gauge will never go into short (short on DIE from VC1/VC2 to VSS) ?

    Best regards

    Andre