Temperature Alert

(MAX6634/MAX6635)

ALERT has programmable polarity and two modes:

comparator and interrupt. Polarity and mode are select-

ed through the Configuration register (Table 4). The

ALERT output is open drain.

Interrupt Mode

With ALERT in interrupt mode, the MAX6634/MAX6635

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.

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

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

register, is equal to the depth of the fault queue. ALERT

deasserts when the number of consecutive conversions

is equal to the depth of the fault queue.

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

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-

register, OVERT is asserted. OVERT only deasserts

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

12-Bit Plus Sign Temperature Sensors with

______________________________________________________________________________________

11

3

8

VCC

+3V TO +5.5V

MAX6634

RELAY

5VDC, 20mA

125VAC, 1A

2N3904

HEATER

SUPPLY

HEATER

4

4k

Ω

ALERT

Figure 10. Simple Thermostat

3

10k

Ω

8

+3V TO +5.5V

+12V

MAX6635

4

12V 300mA

MOTOR

FAN

LOGIC-LEVEL

MOSFET

OVERT

Figure 11. Fan Controller