I require a -15V line, fed from a 15V-18V supply.
Since I have previous experience with the TPS40200, and it seems to fit the additional inverting configuration requirements, I would like to proceed with this chip.
I have done a bit of research:
And a post from Peter Miller in a different thread:
"You could use 2 TPS40200 controllers, one in a standard BUCK configuration to generate the +15V rail and the second in an inverting Buck-Boost configuration to generate the -15V rail.
The inverting Buck-Boost configuration is the same as the BUCK, only you connect the output of the BUCK to the system ground and the ground of the BUCK to the negative output."
My question is in regards to the difference between ground, and the system ground that Peter Miller mentioned. I have attached a picture of my schematic for reference.
You can see I have my GND and VOUT (-15V) switched as per the reports I've read.
What do I connect C3, C5, and C11 to? is this another system ground, and in that case do they go to -15V? or do they remain as true ground?
Do I need to add a cap to my input line to VOUT? This was mentioned in the reports I read, but absent from Peter's simple instructions.
Thank you for your time.
The -15V will be the ground reference for TPS40200, therefore, C3, C5 and C11 should refer to -15V.
Yes, you will need to add a cap between input and -15V Vout, which provides a clean bias supply for the TPS40200.
The following app note may also be useful for you.
The app notes doesn't works. I've tried to start up D-DC TPS40200 with output -15V @300mA, but it doesn't start.
The simulation based on slvm023 and tuned for -15V works good, in real prototype nothing. Some advise, please.
Thank you, Gadi
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