30 | Cheetah 36XL Product Manual, Rev. E |
ST39205
For drives using
For drives using low voltage differential interface circuits, typical power dissipation under idle conditions is 7.5 watts (25.6 BTUs per hour).
To obtain operating power for typical random read operations, refer to the following two I/O rate curves (see Figures 10). Locate the typical I/O rate for a drive in your system on the horizontal axis and read the corre- sponding +5 volt current, +12 volt current, and total watts on the vertical axis. To calculate BTUs per hour, mul- tiply watts by 3.4123.
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I/Os per Second
5V A
12V A 
Watts
Watts
Figure 11. ST39205 DC current and power vs. input/output operations per second (LVD)
6.4Environmental limits
Temperature and humidity values experienced by the drive must be such that condensation does not occur on any drive part. Altitude and atmospheric pressure specifications are referenced to a standard day at 58.7°F (14.8°C). Maximum wet bulb temperature is 82°F (28°C).
6.4.1Temperature
a.Operating
With cooling designed to maintain the case temperature, the drive meets all specifications over a 41°F to 131°F (5°C to 55°C) drive ambient temperature range with a maximum temperature gradient of 36°F (20°C) per hour. The enclosure for the drive should be designed such that the temperatures are not exceeded. Air flow may be needed to achieve these temperature values (see Section 8.3). Operation at case tempera- tures above these values may adversely affect the drives ability to meet specifications.
The MTBF specification for the drive is based on operating in an environment that ensures that the case temperatures specified are not exceeded. Occasional excursions to drive ambient temperatures of 131°F (55°C) or 41°F (5°C) may occur without impact to specified MTBF. Air flow may be needed to achieve these temperatures. The maximum allowable continuous or sustained HDA case temperatures for rated MTBF is 122°F (50°C).
To confirm that the required cooling for the HDA is provided, place the drive in its final mechanical configu- ration, perform random write/read operations. After the temperatures stabilize, measure the case tempera- ture of the drive.
