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2.16.3 Rapid Shutdown
COM Express Modules may support rapid shutdown. On a Module equipped with rapid shutdown, the
assertion of the RAPID_SHUTDOWN input will cause the internal power supply regulators on the
Module to be disabled, and for all residual voltages on the internal power supply rails to be discharged
through crowbar circuits.
Modules supporting rapid shutdown shall specify the power rail discharge behavior, including discharge
time constants and end-of-discharge voltages. An example of such a specification is "all internal power
supply rails must decay to 37% of initial value within 300uS of RAPID_SHUTDOWN assertion, and to a
voltage below 1.5V within 2mS of RAPID_SHUTDOWN assertion."
A rapid shutdown implementation also requires supporting circuitry on the Carrier Board. Upon the
assertion of RAPID_SHUTDOWN, the 12V (main) input power to the Module shall be removed by
Carrier board circuitry and the input power pins shall be externally clamped to ground though a crowbar
circuit located on the Carrier Board. This clamping circuit shall maintain a maximum resistance of 1 ohm
and shall be active for a minimum of 2mS following the rise of RAPID_SHUTDOWN. The Module shall
be designed with sufficiently low input capacitance to allow the input discharge specification to be met
with a 1 ohm discharge resistance.
The Module design should prevent overheating or damage to any Module circuitry in the event that
RAPID_SHUTDOWN is asserted without the removal of input power. This condition could occur due to
malfunction of the Carrier Board support circuitry, or if the RAPID_SHUTDOWN signal is inadvertently
asserted when the Module is installed on a Carrier Board that does not implement rapid shutdown
support circuitry.
In some system implementations the power for both the Module and Carrier Board will fail shortly after
the RAPID_SHUTDOWN signal is asserted. Therefore, the driving source for the RAPID_SHUTDOWN
pin typically must charge an RC circuit on the Module that maintains crowbar assertion for several
milliseconds following power failure. In order to charge this RC circuit rapidly, the RAPID_SHUTDOWN
signal shall be sourced from a source impedance of 50 ohms or less. The RAPID_SHUTDOWN signal
also shall have a rise time of <=1us and shall have a duration of >=20 uS. If the same
RAPID_SHUTDOWN signal source is used to drive the Carrier Board input clamp circuitry, then any
additional load from that Carrier Board circuitry needs to be considered in its design.
Table 46 : Thermal Management Signal Definitions
Signal
Pin#
RAPID_SHUTD
C67
OWN
Note:
1. SOM-5992 is not support.
*
SOM-5992 is not support.
Description
Trigger for Rapid Shutdown. Must be driven to 5V
though a <=50 ohm source impedance for ≥ 20 μs.
Carrier Board:
N/C if not used.
１１７
I/O
Note
I 3.3V
1
CMOS
5.0V
Suspend/5.0V
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