Hi
I have an 5V application with a 0.47 (1ohm ESR) supercapacitor which is used as backup supply when the external supply is disconnected.
During power on, I would like to reduce the inrush charge current to max ~500mA. I have considered several solutions and have now stumbled upon the TI load switches which seems to be a possible solution.
The circuit looks something like this:
The empty box represents the load switch. When the external supply disconnects, VIN goes to zero and the cap (C1) supplies the load, allowing for secure shutdown. During boot and normal operation, the load can be supplied directly from Vin (not needed to wait for C1 to fully charge).
One of the main concerns is that C1 should not discharge back through the load switch towards the input when the external supply is disconnected. Also, as I do already have a voltage drop across D2, I need the drop over the load switch to be small.
The load switch should support the following:
- Adjustable charge time up to several seconds (in order to stay below 500mA)
- Reverse current protection (such that C1 does not discharge back through the load switch)
- > 500mA continuous current
- 5V in
- Low drop down
- Low price
- Good availability
I have been looking at the following parts
TPS22929D
- Good availability
- Low price
- Reverse current protection
- NO adjustable rise time
TPS22918
- Good availability
- Low price
- Adjustable rise time
- NO reverse current protection
TPS22953
- Not as good availability
- Higher priced (over spec'en in regards to current)
- Reverse current protection
- Adjustable rise time
The TPS22953 seems to be the only single output part supporting both reverse current protection and adjustable output - can this be true?
Question:
Would you recommend using the TI load switches for such an application as this one (Please note that the required rise time in this application is much longer than the examples given in the datasheets)?
If so, which part would you recommend giving the requirements above.
I appreciate any help you can provide.
Thanks
Christian