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4.4 Power Distribution
System Architecture
For public disclosure
The mCOM10-L1500 module draws all required load current from the carrier board
through the COM Express connector. There are three power sources:
•
RTC (VCC_RTC)
•
Standby (VCC_5V_SBY)
•
Primary (VCC_12V)
RTC battery power is required and must be stable prior to the application of standby or
primary power. Standby power is optional, but must be supplied if standby operation is
required, such as S3 suspend-to-RAM state. The mCOM10-L1500 is compatible with
wide input range (4.75 to 20 V) primary power, as defined in the PICMG COM.0, R2.1
specification for mini modules. Internally, the standby and primary inputs are diode
OR-ed to form an auxiliary power rail (VIN_AUX), which is used to supply the memory
and other standby circuits.
4.4.1 Supervision and Reset
The Supervision module is responsible for all payload power sequencing and device reset
control. Hard reset sources include startup, overtemperature, watchdog timeout, system
reset from the carrier, and debug header.
4.4.2 Power Reset Sequence
VCC_RTC must be present for a minimum of five seconds prior to the application of
standby or primary power to ensure proper board operation. This will not be an issue for
battery-backed systems other than the initial battery installation. For battery-less systems,
the carrier board must hold off standby and primary power to meet the five second
requirement when the system powers up. Once VCC_5V_SBY or VCC_12V is applied, the
on-board standby supplies will power up and the module enters the S5 state.
To move from standby to active state, primary power, (VCC_12V) must be applied and
stable with PWR_OK as True, and the power button signal (PWRBTN#) must be asserted.
Once SUS_S5# goes high, the memory supply is enabled. The on-board main supplies
will then power up in sequence. Once all power supplies have started and are stable, CB_
RESET# is released by the module approximately 120 ms later.
4.4.3 Thermal Management
Temperature behavior of the board is influenced by two thermal zones for CPU and
memory. Each zone consists of two thresholds, T(HOT) and T(CRIT). If the hot threshold
is reached, an ACPI-aware operating system (such as Microsoft
shutdown to S4 with no data loss. If the critical threshold is reached, an emergency
shutdown to S5 is forced immediately. Non-ACPI aware operating systems (such as DOS
or VxWorks) only provide an emergency shutdown to S5 when the critical threshold is
reached. Overheating of the carrier can be signaled to the module by asserting #THRM. A
high to low edge is detected by the embedded controller, and an ACPI event is sent to the
operating system.
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GFK-2896 Hardware Reference Manual 29
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