Datasheet

Temperature Alert (MAX6634/MAX6635)
ALERT has programmable polarity and two modes:
comparator and interrupt. Polarity and mode are selected
through the Configuration register (Table 4). The ALERT
output is open drain.
Interrupt Mode
With ALERT in interrupt mode, the MAX6634/MAX6635
look for a THIGH or a TLOW fault. The ALERT pin asserts
an alarm for an undertemperature fault, as well as for an
overtemperature fault. Once either fault has occurred, it
remains active until deasserted by a read of any register.
The device then begins to look for a temperature change
crossing the hysteresis level. The activation of ALERT is
subject to the depth of the fault queue.
For example: If T
HIGH
is set to 100°C, T
HYST
is set
to 20°C, and the fault queue depth is set to 4, ALERT
does not assert until four consecutive conversions
exceed 100°C. If the temperature is then read through
the I
2
C-compatible interface, ALERT deasserts. ALERT
asserts again when four consecutive conversions are
less than 80°C.
Comparator Mode
In comparator mode, ALERT is asserted when the num-
ber of consecutive conversions exceeding the value in
the T
HIGH
register, or lower than the value in the T
LOW
register, is equal to the depth of the fault queue. ALERT
deasserts when the number of consecutive conversions
less than T
HIGH
- T
HYST
or greater than T
LOW
+ T
HYST
is equal to the depth of the fault queue.
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, ALERT
does not assert until four consecutive conversions exceed
100°C, or are below 80°C. ALERT only deasserts if four
consecutive conversions are less than T
HIGH
- T
HYST
or
greater than T
LOW
+ T
HYST
.
Comparator mode allows autonomous clearing of an
ALERT fault without the intervention of a master and is
ideal to use for driving a thermostat (Figure 10).
Overtemperature Alarm (MAX6635)
The MAX6635 also includes an overtemperature output
that is always in comparator mode. Whenever the tem-
perature exceeds a value in the programmable T
MAX
register, OVERT is asserted. OVERT only deasserts
after the temperature drops below T
MAX
- T
HYST
. When
the fault queue is activated, OVERT is subject to that
queue, which sets the number of faults that must occur
before OVERT asserts or deasserts. This helps prevent
spurious alarms in noisy environments.
Comparator mode also allows autonomous clearing of an
OVERT fault without the intervention of a master and thus
is ideal to use for driving a cooling fan (Figure 11). In this
application, the polarity of OVERT is active high.
Shutdown
The MAX6633/MAX6634/MAX6635 feature a shutdown
mode, accessible through the serial interface that
saves power by turning off everything except the POR
Figure 11. Fan ControllerFigure 10. Simple Thermostat
3
10kΩ
8
V
CC
+3V TO +5.5V
+12V
MAX6635
4
12V 300mA
MOTOR
FAN
LOGIC-LEVEL
MOSFET
OVERT
3
8
V
CC
+3V TO +5.5V
MAX6634
RELAY
5VDC, 20mA
125VAC, 1A
2N3904
HEATER
SUPPLY
HEATER
4
4kΩ
ALERT
MAX6633/MAX6634/
MAX6635
12-Bit Plus Sign Temperature Sensors
with SMBus/I
2
C-Compatible Serial Interface
www.maximintegrated.com
Maxim Integrated │ 11