18 ST11950 and ST12550 Installation Guide, Rev. D

continued from previous page

2A −10% tolerance is permissible during initial start of the
spindle but must return to ±5% before reaching 7,200 RPM.
The ±5% must be maintained after the drive signifies that its
power-up sequence has been completed and that the drive
is able to accept selection by the host initiator.
3See the +12V current profile in the

Product Manual

.
4This condition occurs when the Motor Start option is en-
abled and the drive has not yet received a start motor
command.
5See “Conducted noise immunity” in the

Product Manual.

The specified voltage tolerance is inclusive of ripple, noise,
and transient response.
6At power-up, the motor current regulator limits the +12V
current to an average value of less than 2.0A, although
instantaneous peaks may exceed this value. These peaks
should measure 5 msec duration or less.
7Minimum current loading for each supply voltage is not less
than 7% of the maximum operating current shown.
8Use separate ground returns for +5 and +12V supplies.
9Where power is provided to multiple drives from a common
supply, carefully consider individual-drive power require-
ments. Where multiple units are powered on simultaneously,
be sure the peak starting current is available to each device.
10Operating condition is a third-stroke seek at OD and read
one track. The command is issued every 0.07 seconds.

continued