When the IC runs without load, the negtive output voltage is within regulation; but after I attach a nominal load resistor, the negtive output voltage increase to almost 0V. Is the IC damaged?
No. There are two possible causes.
First, the VREF pin has only been characterized for output currents up to 10uA as shown in the electrical charateristics table. Your resistor between VREF and FB pins may too small and is causing VREF to fall out of regulation.
Second, an inverting buck-boost converter like the VNEG rail produces significant switching noise. This switching noise can couple back into the IC through the FB and VNEG pins and false trip the current limit circuit of the power switch. Therefore, the switch turns off too early and causes the converter to be power limited. The app note at the link http://focus.ti.com/lit/an/slva219/slva219.pdf explains this in more detail. If you copy the TPS63700 EVM's board layout as documented in the user's guide at the link http://focus.ti.com/lit/ug/slvu134a/slvu134a.pdf on your board, the switching noise will be minimized and should not power limit the converter.
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.