Product Features
WD Scorpio MX375M
22
RELEASED 11/17/10 (WD CONFIDENTIAL)
2679-771293-A01
could also be a problem with backward compatibility. Both these issues need new specification items in
drive specifications to set limits for both the disk drive designers and designers of hot plug enclosures.
3.7.1.6
Hot Plug Removal Issues
Generally, removal of hot plug disk drives does not present any technical issues. Drives are usually in a
low power state prior to removal. Decoupling capacitors in the disk drive will continue to provide
power long enough to soften the sudden loss of current. Bulk capacitors in the power supply and
backplane will absorb the drop in power long enough for the regulators to adjust.
3.7.1.7
ESD Issues
Prior to insertion, disk drives can have static charges of thousands of volts relative to the enclosure. This
charge needs discharging during the insertion process. If insertion guides are ESD resistive, they will
discharge the static charge prior to contact with the mating connector. If the guides are not conductive,
then any static charge will discharge at first contact of the mating connector ground pins. This sudden
discharge will normally not cause any problems because the static charge of the disk drive is common
mode to all internal circuitry making internal differential current and voltages low during discharge.
Because of the unpredictable nature of ESD, use of ESD resistive (not metal) insertion guides is a safer
solution since it gradually discharges any static charge. Having the disk drive enclosed in a canister also
helps ensure proper discharge. It is the responsibility of the hot plug enclosure designer to handle ESD
issues in a safe manner.
3.7.1.8
Drive Canisters
Hot pluggable disk drives can be enclosed in a canister for added protection. This added protection is
both mechanical and electrical. The main electrical protection is from ESD. Canisters prevent any local
discharge onto sensitive parts of the disk drive during handling and insertion. Canisters do increase the
cost of the system.
3.8
Active LED Status
The drive supports external LED requirements. It provides an activity LED output which is ON
during command execution and OFF otherwise.
The drive strength of this open Drain Drive Active signal is that it can sink 12mA to 0.4V Max. It is
5V tolerant, meaning that the external LED may be driven from +5V or +3.3V so long as the Host
system provides a series resistor to limit the LED current to the lower of 12mA or the rated operating
current of the LED. As an example with +5V and a 2 volt forward drop across a 10mA LED, a 300
Ohm 5% 1/16W resistor would be suitable. In the case of a 3.3V supply for the same LED, the resistor
would be 130 Ohm 5% 1/16W.
The pin corresponding to P11 shall be used for Active LED (see “Device Pin Connector Pin
Definitions” on page 11).
