MIC284 Datasheet, PDF (12/20 Pages) Micrel Semiconductor – Two-Zone Thermal Supervisor Advance Information

MIC284
If the device is shut down while in interrupt mode (mode = 1),
the /INT pin will be unconditionally de-asserted and the
internal latches holding the interrupt status will be cleared.
Therefore, no interrupts will be generated while the MIC284
is in shutdown mode, and the interrupt status will not be
retained. Regardless of the setting of the MODE bit, the state
of /CRIT and its corresponding status bit, CRIT1, does not
change when the MIC284 enters shutdown mode. They will
retain their states until after the device exits shutdown mode
and resumes A/D conversions. Since entering shutdown
mode stops A/D conversions, the MIC284 is incapable of
detecting or reporting temperature events of any kind while in
shutdown. Diode fault detection requires one or more A/D
conversion cycles to detect external sensor faults, therefore
diode faults will not be reported until the MIC284 exits
shutdown (see "Diode Faults" above).
Fault Queues
Fault queues (programmable digital filters) are provided in
the MIC284 to prevent false tripping due to thermal or
electrical noise. The two bits in CONFIG[4:3] set the depth of
Fault_Queue. Fault_Queue then determines the number of
consecutive temperature events (TEMPx > T_SETx, TEMPx
< T_HYSTx, TEMP1 > CRIT1, or TEMP1 < nCRIT1) which
must occur in order for the condition to be considered valid.
There are separate fault queues for each zone and for the
over-temperature detect function. As an example, assume
the part is in comparator mode, and CONFIG[4:3] is pro-
grammed with 10_b. The measured temperature in zone one
would have to exceed T_SET1 for four consecutive A/D
conversions before /INT would be asserted or the S1 status
bit set. Similarly, TEMP1 would have to be less than T_HYST1
for four consecutive conversions before /INT would be reset.
Like any filter, the fault queue function also has the effect of
delaying the detection of temperature events. In this ex-
ample, it would take 4 x t_CONV to detect a temperature event.
The depth of Fault_Queue vs. D[4:3] of the configuration
register is shown in Table 4:
CONFIG[4:3]
00
01
10
11
* Default setting
Fault_Queue Depth
1 conversion*
2 conversions
4 conversions
6 conversions
Table 4. Fault_Queue Depth Settings
Interrupt Generation
Assuming the MIC284 is in interrupt mode and interrupts are
enabled, there are five different conditions that will cause the
MIC284 to set one of the status bits (S0, S1, or CRIT1) in
CONFIG and assert the /INT output and/or the /CRIT output.
These conditions are listed in Table 5. When a temperature
event occurs, the corresponding status bit will be set in
CONFIG. This action cannot be masked. However, a
temperature event will only generate an interrupt signal on /
INT if it is specifically enabled by the interrupt mask bit (IM =0
in the configuration register). Following an interrupt, the host
Micrel
should read the contents of the configuration register to
confirm that the MIC284 was the source of the interrupt. A
read operation on any register will cause /INT to be de-
asserted. This is shown in Figure 5. The status bits will be
cleared once CONFIG has been read.
Since temperature-to-digital conversions continue while /INT
is asserted, the measured temperature could change be-
tween the MIC284’s assertion of /INT or /CRIT and the host’s
response. It is good practice for the interrupt service routine
to read the value in TEMPx, to verify that the over-tempera-
ture or under-temperature condition still exists. In addition,
more than one temperature event may have occurred simul-
taneously or in rapid succession between the assertion of
/INT and servicing of the MIC284 by the host. The interrupt
service routine should allow for this eventuality. Keep in mind
that clearing the status bits and deasserting /INT is not
sufficient to allow further interrupts to occur. TEMPx must
become less than T_HYSTx if the last event was an over-
temperature condition, or greater than T_SETx if the last
event was an under-temperature condition, before /INT can
be asserted again.
Putting the device into shutdown mode will de-assert /INT
and clear the S0 and S1 status bits. This should not be done
before completing the appropriate interrupt service routine(s).
/CRIT Output
If and when the measured remote temperature exceeds the
value programmed into the CRIT1 register, the /CRIT output
will be asserted and CRIT1 in the configuration register will be
set. If and when the measured temperature in zone one
subsequently falls below the value programmed into nCRIT1,
the /CRIT output will be de-asserted and the CRIT1 bit in
CONFIG will be cleared. This action cannot be masked and
is completely independent of the settings of the mode bit and
interrupt mask bit. The host may poll the state of the /CRIT
output at any time by reading the configuration register. The
state of the CRIT1 bit exactly follows the state of the /CRIT
output. The states of /CRIT and CRIT1 do not change when
the MIC284 enters shutdown mode. Entering shutdown mode
stops A/D conversions, however, so their states will not
change while the device is shut down.
Polling
The MIC284 may either be polled by the host, or request the
host’s attention via the /INT pin. In the case of polled
operation, the host periodically reads the contents of CONFIG
to check the state of the status bits. The act of reading
CONFIG clears the status bits. If more than one event that
sets a given status bit occurs before the host polls the
MIC284, only the fact that at least one such event has
occurred will be apparent to the host. For polled systems, the
interrupt mask bit should be set (IM = 1). This will disable
interrupts from the MIC284, and prevent the /INT pin from
sinking current. The host may poll the state of the /CRIT
output at any time by reading the configuration register. The
state of the CRIT1 bit exactly follows the state of the /CRIT
output.
MIC284
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September 29, 2000