You can check your Macintosh System Profile. When you select the installed eSATA card, the Device ID will show either "0x6081" or "0x5081". The 3 Gigabit/second eSATA cards use the Marvell chip 88SX6081. The 1.5 Gigabit/second eSATA cards use the Marvell chip 88SX5081.
This condition occurs when the System Preferences Energy Saver Put the hard disk(s) to sleep when possible checkbox is checked (on), or the Disk Sleep Timer is enabled; the Tempo-X SATA card using firmware version 1.2 does not support disk sleep.
To correct this issue, update the Tempo-X card's firmware to version 2.0 or later. Download and run the installer to add disk sleep support.