This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
Hello,
I have a customer evaluating the BQ25710 for a new design and we have a question regarding the BATFET selection.
The data sheet section 9.4.1.1 System Voltage Regulation with Narrow VDC Architecture states this, “The BATDRV pin is only able to drive a battery MOSFET with Ciss lower than 5nF. The Ciss in the range of 1nF~3nF is recommended." The P Channel FET that they are currently considering using is the TPN4R712MD,L1Q which has 4.3nF TYP Ciss but if they consider device variation and 30% tolerance they can expect some of the devices to have Ciss up to 5.6nF which is out of spec. Can you describe for us what failure would occur when the Ciss exceeds 5 nF? Will it cause a catastrophic failure of some device or will it cause the overall charger/monitor to not meet some function or performance metric?
Also, are there better TI recommended alternatives for the BATFET which would be better suited for this socket?
Best regards,
Matt Calvo
Hi, Matt,
Other than the switching FET driver, the BATDRV is a weak source. It may take longer to turn-on and turn-off the BATFET if too much Ciss. Consequently, it may not respond quickly to some protection features such as BATTERY SHORT. Please follow our EVM suggested BATFET as starting point.
Thanks for the feedback Tiger! :)
Based on the EVM User's Guide it looks like they are using the CSD25402Q3A as their BATFET in that design which is Q7 in the design schematic so we will go ahead and use that as a starting point.
-Matt Calvo
Hi Tiger,
Can you list all the protection features that will be affected by longer switching times, in addition to BATTERY SHORT? We need to assess all implications in our application.
The EVM suggests CSD25402Q3A which is not available, so we are considering alternative parts.
--Dugan
Hi Tiger,
Can you provide a complete list of features that will be affected by too much Ciss?
Sorry for the repeat question, I was having trouble posting and had to change my email.
Any protection depending on the BATFET switch-over may be impacted.
My suggestion is to find an alternative part similar to CSD25402, try it in the circuitry. You may find our charger has wide tolerance on the Ciss.