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Original question:

BQ21040: Question about TTDM mode

BQ21040: Question about TTDM mode

chentsu chung
Mastermind 6180 points
Part Number: BQ21040

Hi Bill,

But in our testing, only disable TTDM, then #CHG can goes low when battery insert.

1) According to datasheet 8.4.6, is this descript what I have tested?

 If the battery was removed then the CHG terminal will go
to its high impedance state if not already there. If a battery is detected the CHG terminal does not change states
until the current tapers to the termination threshold, where the CHG terminal goes to its high impedance state if
not already there (the regulated output will remain on).

2) Sorry I don't get it. Do you mean I can reduce resistor from 237K?

3) How the 237K be calculated?

  • 0
    TI__Guru**** 167396 points
    Hi Chentsu,

    Regarding 1, section 8.4.6 is discussing how the charger behaves when it senses a change in TS pin voltage, either because the entire battery pack + thermistor is removed or because only the voltage on TS has changed. For example, if the battery pack remains connected but the TS pin has been forced high or only the thermistor is removed, the charger runs a charge detect cycle to confirm that the battery is still present and then does not change the /CHG output. /CHG should go low when a new battery is attached and charging has started.

    Regarding 2 and 3, with a 237k resistor from TS to GND, the TS pin current source cannot raise the voltage on TS to the TTDM threshold. as shown in figure 6 page 11.