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Hi,
I wish to use the bq24735 and the bq40Z50 for a 4 cell Lithium Ion battery system. I have ordered both EVMs. I wish to clarify
Thanks
You can connect both devices to the SMBus, because they use different addresses. I think that the UVLO feature on the charger is different that what would would want to use to control the load. It shuts down the charger if the voltage goes too low, but the threshold is lower than your would want to use with a 4S application.
I have a question on the same topic.
It appears as if both the bq24735 charger and the bq40Z50 both connect directly to the PACK+ and PACK-. Yet both boards are independent. Does the bq40Z50 know when the charger is applying current to the PACK+ and PACK- and behave accordingly? (ie safely). Is this the normal relationship you would use to charge a PACK using the bq24735 and the bq40Z50 ?
Thanks
The only interaction between these devices is that the bq40z50 can send broadcast commands to request a charging voltage and current from the charger. It will also send charging fault and flag data, as necessary. If the charger and load are enabled, then current will flow from the charger to the load and not through the bq40z50's sense resistor. The batteries can supply current that the charger does not provide and the gauge will sense this current. It would be better to disable the charger, if you do not want it to operate in this manner.
Hello,
Background:
I am charging a 4S battery pack configuration (1cell = 365 mAh) currently using the bq24735 evaluation board, bq24735evm. I've settled into these settings with some success:
With these settings and no load on the evaluation board J2(SYS), supply V2 = OFF, and supply V1 = Vin = 19.5 V, I've successfully charged the 4S depleted battery pack (~13.0 V) up to full charge (16.2 V) in less than three hours.
The issue:
SMBus communication ceases when I turn Vin OFF. Turn Vin back ON and use EV2300 interface board and the software to Read the registers, bq24735 experiences a Power On Reset (POR) and restores the defaults for Charge Option, Charge Current, Charge Voltage, and Input Current. I don't intend on using the EV2300 or a microcontroller to feed the registers every time I plug this battery pack in for a charge. I would really like to Write my registers and have these setting hold after power cycling -- but it doesn't look like this chip can do it alone, no flash memory. If I can't hold these settings, what are my options to fill these registers after power cycle?
Thomas mentioned above: "...bq40z50 can send broadcast commands (on Pack lines ?) to request charging voltage and current from the charger (bq24735 ?)". A quick look at bq40z50 and its evaluation module tells me that it has flash memory capability. Is there a guide on using the bq40z50 and bq24735 together?
Please advise. Thanks!
Philadelphia,
I am not aware of an applications note that covers this subject, but the implementation is fairly simple. The bq40z50 will broadcast the ChargingCurrent and ChargingVoltage to the host and smart charger approximately every 10 seconds. This time can be delayed to up to 60 seconds if the device is busy with an operation. The BCAST bit needs to be set to enable the feature and the Package Error Checking configuration bits need to be set to what the host or charger use. The host and charger are usually set to SMBus address 10 and 12 and are just placed on the same bus. I did attach a document that offers some information on broadcast mode.
Tom
Tom,
It seems this requires a host to feed the values to the bq24735 after power up, every time you charge. I am trying to do it without a microcontroller... here's a test I have conducted towards that goal:
I am aware from the datasheet that in order to keep the SMBus alive you need two conditions:
1) Vvcc > UVLO
2) Vacdet > 0.6 V
I have hard-wired my circuit such that these conditions are met. The SMBus stays alive and my register values remain in the bq24735. However, I am seeing a very high Leak Current from the battery while the external power adapter is not present. I am measuring Leak Current approximately 2.5 mA with an ammeter in line with J2(BATT,GND). I want this Leak Current in the ballpark of 10 uA while battery is not loaded or being charged.
Can you think of any design alternatives without a microcontroller that will keep the custom charge values in the bq24735 while keeping the Leak Current low? Should I instead be looking at some Stand Alone control interface modules (e.g. bq246xx family)?
Thank you for the help!
Philadelphia,
I will need to work with this on the bench and I will try to get back with you in a few days.
Tom
