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Hi there
Very interested in using the BQ25895 IC to solve a couple of problems. I am trying to understand what is possible with this, so I have the following hypothetical questions:
1/ With BATFET being controllable via I2C, if this is switched off via I2C but Vbus is still powered, does the IC provide a regulated supply on VSYS still? Similar to how it would behave if no battery where connected (even though it actually is - but forced so it won't battery supplement).
2/ If I had a large supercapacitor on SYS that was pre-charged to a level above the minimum SYS voltage and VBUS not connected, I assume BATFET will be switched off? Would the IC use any significant current?
3/ Not related to the above two questions: Quiescent current: I assume that with VBUS unconnected and simply a charged battery present on BAT whilst no current is being drawn on SYS, then quiescent current should be < 60uA?
Thank you in advance.
Hi Jeff
Thank you for the replies.
I assume for point 2, if the SYS was the source to charge the supercapacitor (and it was current limited appropriately), the maximum supply voltage would be defined by MINSYS i.e. 3.7V? or would it be possible to supply greater than this?
Further to this, I have three more questions:
1/ Are there any other devices with similar VinDPM ranges? Minimum charge + supply current 2A. Ideally the VinDPM range should be up to 8V. I don't mind this being set with resistors, provided the charge voltage is programmable (or settable) via I2C or using resistors.
The BQ25895 has a VinDPM 2.6 - 15.3V. Most other devices has a much lower range (up to 5.08V or similar).
2/ What is the transient response time of VinDPM i.e. if the input voltage changes, how quickly should it react. I have some indicators of this from some of the traces, but no hard figures or scope shots with the timescales set appropriately.
3/ Maximum voltage input for BQ24895 - The recommended operating range is 3.9 - 14V. The absolute maximum is 22V. I feel this is unusual compared to other similar parts e.g.
- BQ24163 = 10.5V max operating voltage, 18V input voltage (non operating), 20V absolute maximum.
- BQ24193 = 17V max operating voltage, 22V absolute maximum.
If I wanted to run 17V DC into the BQ24895 indefinitely, would this be acceptable?
Thanking you again in advance.
BQ24163 |
Thanks Jeff, very helpful.
Finally, relating to 3/ again, I am comfortable with it not functioning above 13.5V. What I would like to know is if it is safe to run 17V into this input indefinitely (but I understand it will not charge unless < 13.5V). i.e. will there be damage caused by this. Ideally a figure for the maximum recommended input voltage (non-operating) for the bq25895.
My suspicion is that it would be fine (given specification from bq24163) but I would like some confirmation - could this be checked with the design team?
Thanks again
Ok. Now I understand your question. Yes, it is okay to run 17V at this input indefinitely. The input FET is a 20V FET.