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BQ24090: Need for TS Blanking at Battery Insertion?

James Olson
Prodigy 170 points
Part Number: BQ24090
Other Parts Discussed in Thread: BQ24316

Attached to this posting is a schematic of a single cell Li-Ion charger.  The charger contains BQ24090 supervised by BQ24316.

Why did the circuit designer include a 555 timer that zeroes out the TS pin of the BQ24090 for 2 seconds at the time the battery is inserted into the charger?

Battery presence detection is accomplished using pin #6 (BATTERYPRESENT) of battery connector P1.  Internal to the battery module its pin #6 is grounded to the battery's minus pin. 

When the battery module is inserted into the charger the negative-going pulse on BATTERYPRESENT triggers the 555 timer and grounds the BQ24090's TS pin. Why?

18650 Smart Cell Charger.pdf

  • 0
    Prodigy 170 points

    The above posting has garnered 24 views without any remarks.  Maybe I can comment further on my own posting.

    Is it possible that the need for a 2 second TS blanking timer arises from (and this is only a guess) a tendency for the BQ24090 to make a decision on excessively hot battery too quickly after battery insertion into the charger cradle?

    If there is capacitance placed across the 10K temperature thermistor (say, to make TS measurements freer of noise) then immediately after battery insertion the voltage on the TS pin will be low suggesting battery overtemp.  The bandwidth limiting capacitor has not yet had time to charge up to the correct TS value.

    Is there information in the data sheet that tells the time after battery insertion that the "battery too hot/too cold" decision is made?

  • 0 in reply to James Olson
    TI__Guru 67676 points

    Hi James

    This could be related to noise on the TS pin during battery exchange trigger some problem, This was reported by a customer a couple of years ago.  Issue was caused by the sequence pins were connect and ringing on signal.

    Update -- The problem was related to the Charge Complete LED, during battery insertion it was not certain the LED would be ON.  

    Note with this device the Charge Complete LED will only be ON for first charge cycle.