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MAX6635MSA+

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
MAX6633/MAX6634/MAX6635
bit. Registers T
HIGH
and T
LOW
are 16 bits, read/write,
and contain values that trigger ALERT and OVERT.
Register T
HYST
is 16 bits, read/write, and contains the
values by which the temperature must rise or fall
beyond T
HIGH
, T
LOW
, or T
MAX
, before ALERT or
OVERT deassert.
Temperature Conversion
An on-chip bandgap reference produces a signal pro-
portional to absolute temperature (PTAT), as well as the
temperature-stable reference voltage necessary for the
analog-to-digital conversion. The PTAT signal is digi-
tized by the on-board ADC to a resolution of 0.0625°C.
The resulting digital value is placed in the Temperature
register. The temperature conversion runs continuously
and asynchronously from the serial interface at a rate of
500ms per conversion. When the Temperature register
is read, the conversion in progress is aborted. The bus
transaction is completed by a stop condition.
Fault Queue (MAX6634/MAX6635)
A programmable fault queue on the MAX6634/
MAX6635 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 ALERT or OVERT alarm outputs are
toggled. An out-of-tolerance reading is above T
HIGH
or
T
MAX
or below T
LOW
. The fault queue depth defaults to
1 at power-up and may be programmed—through the
Configuration register—to four consecutive conver-
sions. Any time the conversion result is in tolerance,
and the particular alarm output is not asserted, the
queue is cleared, even if it contains some out-of-toler-
ance counts. Additionally, the fault queue automatically
clears at power-up and in shutdown. Whenever the
fault queue is cleared, the alarm outputs are deassert-
ed. Figure 9 is the alarm output and reset diagram.
12-Bit Plus Sign Temperature Sensors with
SMBus/I
2
C-Compatible Serial Interface
10 ______________________________________________________________________________________
**
*
*
*
*IN INTERRUPT MODE, READING THE DEVICE CLEARS ALERT.
OTHERWISE, IT WOULD REMAIN LOW INDEFINITELY UNTIL CLEARED.
T
MAX
T
MAX
- T
HYST
T
HIGH
T
HIGH
- T
HYST
T
LOW
T
LOW
+ T
HYST
ALERT
COMPARATOR MODE
ALERT
INTERRUPT MODE
OVERT
COMPARATOR MODE
ONLY
Figure 9. Alarm Output and Reset Diagram
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
look for a T
HIGH
or a T
LOW
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
MAX6633/MAX6634/MAX6635
12-Bit Plus Sign Temperature Sensors with
SMBus/I
2
C-Compatible Serial Interface
______________________________________________________________________________________ 11
3
8
V
CC
+3V TO +5.5V
MAX6634
RELAY
5VDC, 20mA
125VAC, 1A
2N3904
HEATER
SUPPLY
HEATER
4
4kΩ
ALERT
Figure 10. Simple Thermostat
3
10kΩ
8
V
CC
+3V TO +5.5V
+12V
MAX6635
4
12V 300mA
MOTOR
FAN
LOGIC-LEVEL
MOSFET
OVERT
Figure 11. Fan Controller
MAX6633/MAX6634/MAX6635
and the serial interface. Enter shutdown by program-
ming the shutdown bit of the Configuration register
high. While in shutdown, the Temperature register
retains the last conversion result and can be read at
any time. The ADC is turned off, reducing the device
current draw to 30µA (max). The outputs of ALERT and
OVERT are latched upon entering shutdown, and the
fault queue is held in reset. After coming out of shut-
down, the Temperature register continues to read the
last converted temperature, until the next conversion
result is available.
Thermal Considerations
The MAX6633/MAX6634/MAX6635 supply current is
typically 200µA when the serial interface is inactive.
When used to drive high-impedance loads, the devices
dissipate negligible power; therefore, the die tempera-
ture is essentially the same as the package tempera-
ture. The key to accurate temperature monitoring is
good thermal contact between the MAX6633/MAX6634/
MAX6635 package and the monitored device or circuit.
Heat flows in and out of plastic packages primarily
through the leads. Short, wide copper traces leading to
the temperature monitor ensure that heat transfers
quickly and reliably. The rise in die temperature due to
self-heating is given by the following formula:
ΔT
J
= P
DISSIPATION
x θ
JA
where P
DISSIPATION
is the power dissipated by the
MAX6633/MAX6634/MAX6635, and θ
JA
is the pack-
age’s thermal resistance.
The typical thermal resistance is 170°C/W for the 8-pin
SO package. To limit the effects of self-heating, mini-
mize the output currents. For example, if the
MAX6634/MAX6635 sink 4mA with the maximum
ALERT V
L
specification of 0.8V, an additional 3.2mW of
power is dissipated within the IC. This corresponds to a
0.54°C rise in the die temperature.
Applications Information
Figure 10 shows the MAX6634 used as a simple thermo-
stat to control a heating element. Figure 11 shows the
MAX6635 used as a temperature-triggered fan controller.
Chip Information
TRANSISTOR COUNT: 12,085
PROCESS: BiCMOS
12-Bit Plus Sign Temperature Sensors with
SMBus/I
2
C-Compatible Serial Interface
12 ______________________________________________________________________________________
MAX6633
A3 A2 A1 A0 ADDRESS
GND GND GND GND 1000 000
GND GND GND V
CC
1000 001
GND GND V
CC
GND 1000 010
GND GND V
CC
V
CC
1000 011
GND V
CC
GND GND 1000 100
GND V
CC
GND V
CC
1000 101
GND V
CC
V
CC
GND 1000 110
GND V
CC
V
CC
V
CC
1000 111
V
CC
GND GND GND 1001 000
V
CC
GND GND V
CC
1001 001
V
CC
GND V
CC
GND 1001 010
V
CC
GND V
CC
V
CC
1001 011
V
CC
V
CC
GND GND 1001 100
V
CC
V
CC
GND V
CC
1001 101
V
CC
V
CC
V
CC
GND 1001 110
V
CC
V
CC
V
CC
V
CC
1001 111
MAX6634
A2 A1 A0 ADDRESS
GND GND GND 1001 000
GND GND V
CC
1001 001
GND V
CC
GND 1001 010
GND V
CC
V
CC
1001 011
V
CC
GND GND 1001 100
V
CC
GND V
CC
1001 101
V
CC
V
CC
GND 1001 110
V
CC
V
CC
V
CC
1001 111
MAX6635
A1 A0 ADDRESS
GND GND 1001 000
GND V
CC
1001 001
V
CC
GND 1001 010
V
CC
V
CC
1001 011
Table 1. Address Selection
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

MAX6635MSA+

Mfr. #:
Buy MAX6635MSA+
Manufacturer:
Maxim Integrated
Description:
Board Mount Temperature Sensors 12-Bit + Sign Temperature Sensor
Lifecycle:
New from this manufacturer.
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