BQ24770: Smart Battery

Hi Zeming,

1) The BQ24770 can be used with smart batteries. The smart battery can send ChargeVoltage() and ChargeCurrent() commands to the BQ24770 through SMBus.

2) Yes, the BQ24770 is an SMBus controlled charger. The host must write to the registers in order to enable charging.

3) The BQ24770 does not support PEC. Please disable PEC from the smart battery's broadcasts to the charger.

4) The BQ24770 does not have a TS pin, and it cannot monitor the battery temperature on its own. Typically, our SMBus charge controllers are paired with a battery gauge that monitors parameters such as the state of charge, charge voltage, charge current, battery temperature, etc. The host MCU can make decisions based on this information and control the BQ24770 as needed.

5) and 6) There are several options for this. First, let me explain the functionality of the /BATPRES pin. /BATPRES low tells the BQ24770 that the battery is present, and /BATPRES high tells the BQ24770 that the battery is absent. If /BATPRES goes from low to high, the BQ24770 interprets this as battery removal. The device will exit LEARN mode, disable charging, and reset the ChargeVoltage() and ChargeCurrent() registers. Is this functionality needed in your application?

If the /BATPRES pin functionality is not needed, then you can simply tie /BATPRES to GND in order to indicate to the BQ24770 that the battery is present. This is the simplest solution. Make sure you do not leave the /BATPRES pin floating. Otherwise, a low to high transition will stop charging and reset the ChargeVoltage() and ChargeCurrent() registers, as explained above.

If the /BATPRES pin functionality is needed, then there are a couple options. Some battery packs have an output pin with an internal pull-down resistor, which can be conveniently connected to /BATPRES on the BQ24770. This automatically pulls the /BATPRES pin low when the battery is inserted, which indicates to the BQ24770 that the battery is present. Does your battery have a pin for this?

If the /BATPRES functionality is needed, but the battery pack does not have this output pin, then you can use the BQ24770's independent comparator to detect whether or not the battery is present. In this case, the independent comparator will compare an internal reference voltage with the battery voltage (connected to CMPIN), and CMPOUT (the output of the independent comparator) should connect to /BATPRES. You can use register ChargeOption1() bits[7:4] to set the independent comparator's internal reference voltage, output polarity, and deglitch time.

7) The BQ24770 is a host-controlled charger. The host is responsible for controlling the BQ24770 in order to set the desired charge profile. If you have an LED to indicate when charging is complete, then I would suggest that the host should control this by turning on the LED after charging is done.

Best regards,

Angelo

Hi Zeming,

Please refer to Section 4.11 in the BQ40Z50 technical reference manual. The CPE bit can be used to enable or disable PEC from the broadcasts to the charger. With PEC disabled, there should be no issue controlling the BQ24770.

https://www.ti.com/lit/ug/sluua43a/sluua43a.pdf

Please note that I only support chargers, not gauges. For further questions regarding the BQ40Z50, I recommend opening a new E2E thread for the BQ40Z50 so the gauge team can provide support.

Best regards,

Angelo