Part Number: BQ25896
Hello all,
I am designing the BQ25896 part into a Li-Ion charger. The charger will operate from a stable 12V DC input. Although the charger has I2C control link, I'd like to have an autonomous charging mode as default operation. What I am struggling to understand is how the ILIM external resistor (or PSEL set HIGH to USB input) affect the charging current? As I understand, the power-on default is set to 2A, but if the input side of the device has a limit, say 500mA, obviously I can't get the full default charging current. Actually, I'd like to set the input limits in such a way that the charging current will be just about 1A, for fail-safe operations. I don't believe this relationship is described in the datasheet. Could someone explain how it works?
The Pin Table on page 5 says the following about ILIM pin:
Input current limit Input. ILIM pin sets the maximum input current and can be used to monitor input current
ILIM pin sets the maximum input current limit by regulating the ILIM voltage at 0.8 V. A resistor is connected
from ILIM pin to ground to set the maximum limit as IINMAX = KILIM/RILIM . The actual input current limit is the
lower limit set by ILIM pin (when EN_ILIM bit is high) or IIINLIM register bits. Input current limit of less than 500
mA is not support on ILIM pin.
ILIM pin can also be used to monitor input current when the voltage is below 0.8V. The input current is
proportional to the voltage on ILIM pin and can be calculated by IIN = (KILIM x VILIM) / (RILIM x 0.8)
The ILIM pin function can be disabled when EN_ILIM bit is 0.
I am confused here. What is VILIM? Which voltage can be below 0.8V?
I understand that KILIM is about 355 Ohms +- 10%. If I use RILIM of about 700 Ohms (input limit to ~500mA) will it limit the max battery charge current (ICHG) to about 1A under power-up defaults?
Thanks.
