My customer is planning to use the BQ20z45 and a BQ24747 in a battery pack design and they had the following questions. Can someone help to provide answers?
1.) Can a host controller, through the SMbus, have the AFE disconnect the load from battery and on reconnecting return to normal operation? 2.) When using Bq20z45 with Bq247xx, what is the best approach to isolate the positive charge input be protected & isolated from reverse current (if it is not easy, then I will add an isolation diode)? 3.) What external components can be optimized / eliminated when using Bq20z45 with Bq247xx? Could a single temperature sensing element be used? Could some of the pass switch elements be eliminated? Can they share current sense information (to use one Isense instead of two)? Is there any reason to place a switch (AFE controlled, as in the eval board) between the charger and battery? 4.) Since our intended power supply (for charging) will always be significantly higher voltage than the battery, could we safely replace a mosfet in the charger with a catch diode? 5.) Is there a a.) method, b.) advantage, to sharing information about the charge state that the AFE/Fuel gauge is aware of, to the charger? Could we get into a situation where the fuel gauge sees that more charge could be accepted at the battery, but the charger has “given up” i.e. completed it’s cycle, or gone into float/trickle mode?
1.) Can a host controller, through the SMbus, have the AFE disconnect the load from battery and on reconnecting return to normal operation?
2.) When using Bq20z45 with Bq247xx, what is the best approach to isolate the positive charge input be protected & isolated from reverse current (if it is not easy, then I will add an isolation diode)?
3.) What external components can be optimized / eliminated when using Bq20z45 with Bq247xx? Could a single temperature sensing element be used? Could some of the pass switch elements be eliminated? Can they share current sense information (to use one Isense instead of two)? Is there any reason to place a switch (AFE controlled, as in the eval board) between the charger and battery?
4.) Since our intended power supply (for charging) will always be significantly higher voltage than the battery, could we safely replace a mosfet in the charger with a catch diode?
5.) Is there a a.) method, b.) advantage, to sharing information about the charge state that the AFE/Fuel gauge is aware of, to the charger? Could we get into a situation where the fuel gauge sees that more charge could be accepted at the battery, but the charger has “given up” i.e. completed it’s cycle, or gone into float/trickle mode?
1. The load can be disconnected under SMBus command only if the unit is unsealed. An intentional fault could be introduced, or the special 0x46 command can be used to manipulate the FETs. Leaving a unit unsealed in the field represents a very risky safety hazard, however. Some customers insert auxilliary control lines to manipulate the FETs directly, without SMBus.
2. Yes, use a steering diode on the input.
3. This is a good question. Right now I don't see much opportunity since charger senses current on the high side, while gauge senses on the low side. Temperature reading schemes would interfere. In the future, we will definitely consider some kind of combined device that is optimized.
4. Sorry, don't understand this one. Please clarify, or better yet submit this one to the Charger Forum.
5. Please see attached app note.
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