Yes. UCD90xxx devices may hold clock low while processing the PMBus inquiry. According to PMBus specifications, a host needs to support clock stretching for up to 35 ms. It is recommended leaving a 1-ms interval between two PMBus inquiries; otherwise, the UCD90xxx may occasionally hold clock low for 35 ms and then timeout (hardware release clock line).
For more FAQ please check the following document.
UCD90xxx Family Frequently Asked Questions and Answers
UCD9090 UCD9090A UCD90120 UCD90120A UCD90124 UCD90124A UCD90160 UCD90160A UCD90320 UCD90320U