User manual

43 MIC-3392MIL User Manual
Chapter 3 Pre-heating for the MIC-3392MILC
A heater pad (70 mm x 80 mm) attached to the interior side of the conduction-cooled
plate is capable of providing approximately 10 watts of thermal power when required.
Its power input wire is connected to CN13. It gets a +12 V (with 0.8 A) input from two
J5 connector pins. The following figure illustrates the pin definitions of CN13.
Figure 3.2 Pin definitions of CN13
3.2 Pre-heat Firmware Operation
The pre-heat code in the firmware will be executed when the board temperature (as
measured by DS1631AU) is below a predefined threshold (TEMP_PREHEAT) and
the board is powered on. By default, TEMP_PREHEAT is set at -30° C.
The pre-heat code can be configured to operate in one of two different modes by set-
ting the PREHEAT_MODE register to the appropriate value. The modes are Standard
Pre-heat, and Extended Pre-heat.
3.2.1 Standard Pre-heat Mode
As a default pre-heat mode, the firmware code will keep the system reset asserted
when the payload power is enabled. It will activate the pre-heat circuit by turning on
the appropriate GPIO pin and will:
! Constantly monitor if the payload is switched off again -> turn off preheat circuit
and return to the firmware code’s application main loop.
! Constantly monitor board temperature and de-assert the system reset once the
board temperature rises above TEMP_PREHEAT. It shall keep the preheat cir-
cuit enabled and keep monitoring the board temperature. The preheat circuit will
only be switched off after the temperature rises after a predefined
TEMP_PREHEAT + TEMP_HIST.
Note! More +12 V power to the pre-heat pad can be made available via pins 1
through 3 on CN13, with customized J3 ~ J5 pin definitions and Com-
pactPCI backplane.
Note! TEMP_HIST = Positive temperature hysteresis for preheat circuit deacti-
vation. The default value of the TEMP_HIST is 0° C.