TI seldom sees the request for creating negative rail from a negative rail, so we do not have a specific IC to do this.
Of course you could use a linear regulator, and TI has many negative linear regulators, however the efficiency would be 5/15 or 33%.
Here are 2 that would work for you.
We do have a reference design using a switcher.
Buck Converter for Negative Input and Output Voltages Reference Design
This uses the TPS40210 in a buck configuration.
Since Vout -5V must be referenced to ground, and the IC is referenced to -15Vin, the output voltage must be level shifted with respect to ground. In the schematic you will see Q2 Q3 which perform this function.
You can modify this design to create -5V at 500mA from -15Vin.
Ed WalkerTexas Instruments Online Support - Systems & Tools
In reply to EdWalker:
Dear Mr. Ed Walker,
Thanks for reply,
Actually we don't have sufficient space to incorporate buck converter at PCB board.
Consequently, I went through the part no. UCC284-ep (datasheet as attached) .
By using UCC284-ep LOW-DROPOUT 0.5-A NEGATIVE LINEAR REGULATOR, whether i could able to achieve high efficiency at given attributes
We required efficiency minimum 80%
Please guide me.
In reply to Atul Mishra:
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