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BQ21040: TS pin issue

chentsu chung
Mastermind 6180 points
Part Number: BQ21040

Hi,

What we found:

  1. Use BQ21040EVM-777 and connect TS to GND with 237KOhm(disable TTDM mode) and without battery, the charger VOUT will output voltage if I touch TS pin by finger or anything made by metal, and it recover if finger or the metal thing removed.

  2. TS pin voltage is generate by internal current source and clamp at 2000mV according to datasheet, but some failed IC we measured that TS pin voltage goes to 3~4V, and recover if demount and remount it again.

  3. Add too much cap at TS pin(>100n), the #CHG indicator works abnormal.

  4. In battery remove testing, we tyied to remove 3 pins of battery  pin by pin (because it's impossible all pins touch IC in the same time), if TS pin remove before B+, then #CHG will keep the status and doesn't change, unless we touch TS pin or reset VIN.
  5. Before B+ insert on EVM, if we touch BQ21040's TS pin by battery's TS pin, sometimes the B+ will output voltage(like TTDM performance) 

 Workaround:

1. We remove the NTC from battery and put it on BQ21040's TS pin, the B+ will goes HIGH-LOW-HIGH-LOW...(battery detection)

And there is no any unexpected performance happened again. (but NTC can't sense the temp. of cell in this way)

2. Due to B+ pin must remove early than TS pin, we add 10uF at TS pin, and there are no issue till now(about 10 pcs),


Support Need:

1. End-customer needs to know how those kind of issue happened.

2. End-customer needs to get officially document indecate that BQ21040 is not good for removeable battery pack application.

3. Could you help to provide the spec indecate that the period and the amplitude of battery detaction, spec have only 25ms for typ.value, customer needs to know the Min. and Max. value for SW to know that battery detection happened.

4. Based on Workaround2 (add 10uF at TS pin), could you please have comment at this solution? Is there any side effect?

Thank you very much.
C.T.