Rainbow Electronics MAX6626 - Manual (Page 11)

MAX6625/MAX6626
9-Bit/12-Bit Temperature Sensors with
I 2 C-Compatible Serial Interface in a SOT23
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drain, and the MAX6625R/MAX6626R output includes
an internal 35k
Ω (typ) pullup resistor. Figure 6 shows
the OT alarm operation and reset details.
Fault Queue
A programmable fault queue on the MAX6625/
MAX6626 eliminates spurious alarm activity in noisy
environments. The queue sets the number of consecu-
tive out-of-tolerance temperature readings that must
occur before the OT alarm output is toggled. An out-of-
tolerance reading is above T
HIGH or below T LOW . The
fault queue depth defaults to one at power-up and may
be programmed to one, two, four, or six consecutive
conversions. Any time the conversion result is in toler-
ance, and OT is not asserted, the queue is cleared,
even if it contains some out-of-tolerance counts.
Additionally, the fault queue automatically clears at
power-up, in shutdown, or if a master writes to any of
the T
HIGH , T LOW , or configuration registers. Whenever
the fault queue is cleared, OT is deasserted.
For example, the fault queue is set to four, two consec-
utive out-of-tolerance readings have occurred, and the
master writes to the T
LOW register. The fault queue is
cleared and begins to look for four new consecutive
out-of-tolerance conversions.
Comparator Mode
In comparator mode, OT is asserted when the number
of consecutive conversions exceeding the value in the
T
HIGH register is equal to the depth of the fault queue.
OT deasserts when the number of consecutive conver-
sions less than the value in the T
LOW register is equal
to the depth of the fault queue. T HIGH minus T LOW is
the effective hysteresis of the OT output.
For example, if T HIGH is set to +100°C, T LOW is set to
+80°C, and the fault queue depth is set to four, OT will
not assert until four consecutive conversions exceed
+100°C. Then, OT will not deassert until four consecu-
tive conversions are less than +80°C.
Comparator mode allows autonomous clearing of an OT
fault without the intervention of a master and is ideal to
use for driving a cooling fan (Figure 7).
Interrupt Mode
In interrupt mode, the MAX6625/MAX6626 look for a
T
HIGH or a T LOW fault based on previous fault activity.
The OT pin asserts an alarm for an undertemperature
fault, as well as for an overtemperature fault, depending
on certain conditions. If the fault queue is cleared at
power-up, the IC looks for a T
HIGH fault. After a T HIGH
fault, the IC looks for a T LOW fault. After a T LOW fault,
the IC looks for a T HIGH fault, and it will bounce back
and forth if properly deasserted each time. Once either
fault has occurred, it remains active indefinitely until
deasserted by a read of any register, and the device
then begins to look for a fault of the opposite type. Also,
if the fault queue is cleared, OT is deasserted and the
IC once again looks for a T
HIGH fault. The activation of
any fault is subject to the depth of the fault queue.
DIE
TEMPERATURE
TIME
* * *
T HIGH
T LOW
OT
(COMPARATOR MODE)
OT
(INTERRUPT MODE)
TEMPERATURE RESPONSE
SHOWN WITH OT SET FOR
ACTIVE LOW
*THIS ASSUMES DEASSERTION OF OT BY A
MASTER THROUGH THE SERIAL INTERFACE.
SEE INTERRUPT MODE SECTION.
Figure 6. OT Alarm Output and Reset Diagram