BQ21061: Start-up charger current

HI Francesco, 

The information for the charger flow at startup is shown in the BQ21061 Charger Flow Diagram. You are correct that the charger will charge with pre-charge or fast charge depending on the battery voltage.

Francesco Mariottini said:

In our application we do not drive the \CE pin of the BQ21061 therefore the BQ21061

Just to double check here, is the /CE pin low? The BQ21061 does use a prioritization scheme where the /CE pin is prioritized over the CHARGER_DISABLE bit.

Best Regards,

Anthony PHam

Dear Anthony thanks for your answer, but probably I didn't able to explain my doubt. I need to know the BAT pin behaviour at start-up when the voltage on this pin goes from zero towards battery regulation voltage. The start-up procedure in terms of timing sequence that BQ21061 executes during power-up is:

1) BQ21061 measures battery voltage; if this voltage is greater than VLOWV then BQ21061 tries to recharge battery with defualt fast-charge equal to 10mA

2) BQ21061 tries to recharge battery with an unknown initial current (probably 2.5mA pre-charge current) and after that it measures battery voltage and depending if this voltage are greater or lower than VLOWV it uses default fast-charge current or default pre-charge current.

Which is the correct timing sequence of the BQ21061 during start-up, sequence 1 or sequence 2?

The final result using 1 or 2 is almost the same for battery point of view (i.e.to recharge the battery) since the start-up procedure persists for a very short time (some msec.) but it is important for the correct start-up of the Fuel Gauge that we are using. If the start-up procedure of the BQ21061 is the 2) and during start-up the current that BQ21061 can supply on BAT pin is limited and lower than 5mA, the Fuel Gauge that requires this current (5mA) to correctly start-up, could have some problems to start.

Thanks

Francesco

Hi Francesco,

Thanks for the clarification! Let me double check this in the lab. I'll reserve some time and should have an answer by EOD tomorrow. 

Best Regards,

Anthony Pham

Dear Anthony,

the two pictures that you attached seems to be the same relevant to Fast Charge at 100mA. If I well understood you shown me the two cases Fast charge at 100mA and pre-charge with 30mA to better view the difference on the currents, anyway I didn't understand how you could force the BQ21061 to start-up with pre-charge or fast-charge that are not the true default values (respectively 2.5mA and 10mA)

Francesco

Ok, thanks. I have another question. I need to understand with which current BQ21061 starts in another situation that I describe in the text under:

1) Voltage at IN pin of BQ21061 always present

2) BQ21061 start-up, after that our micro initializes the BQ21061 with these currents: Pre-charge=1.25mA, Fast-charge=100mA

3) our micro disables charger (bit CHARGER_DISABLE=1 in ICCTRL2 register, \CE pin floating)  and wait some delay

4) our micro re-enables charger (bit CHARGER_DISABLE=0 in ICCTRL2 register, \CE pin floating)

When our micro re-enables the charger of BQ210161, if VBAT>VLOWV, which is the current with BQ21061 starts to charge battery? I presume 100mA that is the fast-charge current that we set before to disalbe charger since BQ21061 is always powered from voltage at IN pin and therefore it should keep the values that we wrote inside its registers (I  need to understand if BQ21061 after point 4) starts with default fast-charge (10mA), other unknow current, or 100mA fast-charge that we previously sets inside the ICHG_CTRL register)

Thanks

Francesco