FXTH870xD
Sensors
Freescale Semiconductor, Inc.
85
10.7
Thermal Shutdown
When the package temperature becomes too low or too high the MCU can be placed into a STOP mode to suspend operation
and prevent transmission of RF signals which may be corrupted at the temperature extremes. Return to normal operation after
the temperature falls back within the recovery temperature range. The presence of either the low or high temperature shutdown
will disable the PWU from causing either a periodic wakeup or a periodic reset. The MCU, temperature sensor and ADC10 are
all functional over the full temperature range from T
L
to T
H
.
10.7.1
Low Temperature Shutdown
Low temperature shutdown is achieved using temperature readings taken by the ADC10 as described in
and
enabling the thermal restart circuit by setting the TRE bit and selecting the low temperature threshold by clearing the TRH bit.
When the software programmed low temperature is reached the MCU will turn off all operating functions and enter the STOP1
mode.
10.7.2
High Temperature Shutdown
The high temperature shutdown level is determined from a measurement of the temperature sensor by the ADC10 as described
in
and enabling the thermal restart circuit by setting the TRE bit and selecting the high temperature threshold by
setting the TRH bit. When the software programmed high temperature is reached the MCU will turn off all operating functions and
enter the STOP1 mode.
10.7.3
Temperature Shutdown Recovery
The MCU can be restarted by the Temperature Restart (TR) module when the temperature returns within the normal temperature
range, T
RESET
. When this occurs the MCU will be reset and begin execution from the reset vector located at $DFFE/$DFFF. The
TR module can be enabled using the TRE bit in the SIMOPT1 register. The TR module can be powered on and off by setting or
clearing the TRE bit located at bit 3 in the SIMOPT1 register at address $1802. The TRE bit is cleared by an MCU reset.
When the TRE bit is set the TR module can then be set to detect a recovery from either a high temperature or a low temperature
using the TRH in the SIMOPT1 register. The TRH bit is cleared by an MCU reset.
The TR module does not activate an MCU restart and reset unless it has first moved outside the re-arming temperature range,
T
REARM
, as shown in
Figure 58
. The status of the TR can be checked by reading the TRO bit located at bit 0 in the SIMTST
register at address $180F. The TRO bit is set high by an MCU reset. The state of the TRO bit is as follows:
1 = TR module is outside the T
REARM
temperature range and will restart the MCU if the TRE bit is set and
temperature falls back within the T
RESET
temperature range.
0 = TR module is within the T
RESET
temperature range and the MCU cannot be armed to restart when
temperature falls back to the T
RESET
range. The TRE bit cannot be set.
Figure 58. Temperature Restart Response
TRO = 1
TRO = 0
T
RESET
T
REARM
TRO
TEMPERATURE
SHUTDOWN
SHUTDOWN
ACTIVE
T
REARML
T
REARMH
T
RESETL
T
RESETH
TRH = 1
TRH = 0
Содержание FXTH870 D Series
Страница 86: ...FXTH870xD Sensors 84 Freescale Semiconductor Inc Figure 57 Data Flow For Measurements...
Страница 170: ...FXTH870xD Sensors 168 Freescale Semiconductor Inc 19 Package Outline Figure 127 QFN Case Outline...
Страница 171: ...FXTH870xD Sensors Freescale Semiconductor Inc 169 Figure 128 QFN Case Outline...
Страница 172: ...FXTH870xD Sensors 170 Freescale Semiconductor Inc Figure 129 QFN Case Outline...
Страница 173: ...FXTH870xD Sensors Freescale Semiconductor Inc 171...
