19-1852; Rev 1; 3/01
SOT23 Local Temperature Comparators
with SMBus Serial Interface
General Description
The MAX1755/MAX1756 are temperature monitors with
±3°C accuracy, each with a built-in comparator and
SMBus™-controlled variable trip threshold. This DAC-
programmable threshold allows specific thermal zones
and system responses to overtemperature conditions to
be adjusted under software control. The MAX1755/
MAX1756 feature serial programmability, low cost, wide
supply-voltage range, and a tiny package.
The MAX1755 has a self-clearing thermostat output
(OVERT), and the MAX1756 has a latched interrupt out-
put (ALERT). A variety of slave addresses allow for up
to six devices per system (Table 3).
The MAX1755 has 4°C of built-in hysteresis. The
MAX1756 detects both low-to-high and high-to-low tem-
perature transitions within an 8°C temperature window.
This arrangement supports “windowing” algorithms
where the comparison threshold is reprogrammed “on-
the-fly.”
The MAX1755/MAX1756 are offered in the 6-pin SOT23
package and are specified over the -40°C to +125°C
temperature range. For other temperature sensors with
SMBus interfaces, refer to the MAX1617, MAX1618,
MAX1668, and MAX1805 data sheets.
o
Built-In Hysteresis
o
SMBus 2-Wire Serial Interface
o
OVERT
Thermostat Output (MAX1755)
o
ALERT
Interrupt Output (MAX1756)
o
Threshold Accuracy
±3°C (+25°C to +100°C)
±5°C (0°C to +125°C)
o
200µA (max) Supply Current
o
+2.375V to +5.5V Supply Range
o
Tiny 6-Pin SOT23 Package
Features
o
Programmable Temperature Threshold
MAX1755/MAX1756
Ordering Information
PART*
MAX1755AAUT-T
MAX1755BAUT-T
MAX1756AAUT-T
MAX1756BAUT-T
TEMP RANGE
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
PIN-
PACKAGE
6 SOT23-6
6 SOT23-6
6 SOT23-6
6 SOT23-6
TOP
MARK
AANM
AANL
AANO
AANL
________________________Applications
Local Temperature Monitoring
Desktop Computers
Notebook Computers
Servers
Workstations
Memory Modules
Multichip Modules
Industrial Control Systems
Automotive
*A
and B suffixes on these devices select different combina-
tions of slave addresses. See Table 3 to determine the
appropriate suffix.
Note:
Requires a special solder temperature profile described
in the Absolute Maximum Ratings section.
Typical Operating Circuit
0.1µF
+2.375V TO +5.5V
V
CC
MAX1755
MAX1756
SMBCLK
SMBDATA
OVERT
(ALERT)
10kΩ EACH
CLOCK
DATA
INTERRUPT TO
µC
Pin Configurations appear at end of data sheet.
SMBus is a trademark of Intel Corp.
( ) ARE FOR MAX1756 ONLY.
ADD
GND
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
SOT23 Local Temperature Comparators
with SMBus Serial Interface
MAX1755/MAX1756
ABSOLUTE MAXIMUM RATINGS (Note 1)
V
CC
to GND ..............................................................-0.3V to +6V
ADD to GND ...............................................-0.3V to (V
CC
+ 0.3V)
SMBCLK, SMBDATA,
ALERT, OVERT
to GND ........-0.3V to +6V
SMBDATA,
ALERT, OVERT
Current....................-1mA to +50mA
Continuous Power Dissipation (T
A
= +70°C)
6-Pin SOT23 (derate 9.1mW/°C above +70°C)............727mW
Operating Temperature Range (extended) .......-40°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Note 1:
This device is constructed using a unique set of packaging techniques that impose a limit on the thermal profile to which the
device can be exposed during board-level solder attach and rework. The limit permits the use of only the solder profiles rec-
ommended in the industry-standard specification, JEDEC 020A, paragraph 7.6, Table 3 for IR/VPR and Convection reflow.
Preheating is required. Hand or wave soldering is not allowed.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
CC
= +3.3V,
T
A
= 0°C to +125°C,
unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 2)
PARAMETER
TEMPERATURE COMPARATOR AND POWER SUPPLY
DAC Resolution (Note 3)
Temperature Comparison Error
Temperature Hysteresis
Temperature Window
Sampling Frequency
Supply Voltage Range
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis
Power-On Reset Threshold
Operating Supply Current
Standby Supply Current
ADD Input High Voltage
ADD Input Low Voltage
SMBus INTERFACE
Logic Input High Voltage
Logic Input Low Voltage
SMBus Output Low Sink Current
ALERT, OVERT
Output Low Sink Current
ALERT, OVERT
Output High Leakage Current
Logic Input Current (ADD, SMBCLK, SMBDATA)
SMBus Input Capacitance
SMBus Clock Frequency
SMBCLK Clock Low Time
SMBCLK Clock High Time
SMBus Rise Time
SMBCLK, SMBDATA; V
CC
= 2.7V to 5.5V
SMBCLK, SMBDATA; V
CC
= 2.7V to 5.5V
SMBDATA forced to 0.4V; V
CC
= 2.7V to 5.5V
Pin forced to 0.4V
Pin forced to 5.5V
Inputs forced to V
CC
or GND
SMBCLK, SMBDATA
(Note 4)
t
LOW
, 10% to 10% points, V
CC
= 2.7V to 5.5V
t
HIGH
, 90% to 90% points, V
CC
= 2.7V to 5.5V
SMBCLK, SMBDATA; 10% to 90% points,
V
CC
= 2.7V to 5.5V
DC
4.7
4
1
-1
5
100
6
6
1
+1
2.1
0.8
V
V
mA
mA
µA
µA
pF
kHz
µs
µs
µs
V
CC
, falling edge
SMBus static, logic inputs forced to V
CC
or GND
SMBus static, logic inputs forced to V
CC
or GND
0.8 x V
CC
0.2 x V
CC
0.2
V
CC
input, rising edge
Monotonicity guaranteed
T
A
= +25 C to +100 C
T
A
= 0 C to +125 C
With respect to temperature comparison
value (MAX1755)
Lower threshold with respect to temperature
comparison value (MAX1756)
o
o
o
o
CONDITIONS
MIN
2
-3
-5
-4.5
-9
0.50
2.375
2.05
TYP
MAX
UNITS
o
C
C
+3
+5
-4
-8
1
2.2
30
1.7
85
0.8
2.3
200
4
-3.5
o
o
C
-7
2.00
5.5
2.35
kHz
V
V
mV
V
µA
µA
V
V
2
_______________________________________________________________________________________
SOT23 Local Temperature Comparators
with SMBus Serial Interface
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +3.3V,
T
A
= 0°C to +125°C,
unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 2)
PARAMETER
SMBus Fall Time
SMBus Start Condition Setup Time
SMBus Repeated Start Condition Setup Time
SMBus Start Condition Hold Time
SMBus Stop Condition Setup Time
SMBus Data Valid to SMBCLK Rising-Edge
Time
SMBus Data Hold Time (Master Transmitter)
SMBus Data Hold Time (Slave Transmitter)
CONDITIONS
SMBCLK, SMBDATA; 90% to 10% points,
V
CC
= 2.7V to 5.5V
V
CC
= 2.7V to 5.5V
t
SU:STA
, 90% to 90% points, V
CC
= 2.7V to 5.5V
t
HD:STA
, 10% of SMBDATA to 90% of
SMBCLK, V
CC
= 2.7V to 5.5V
t
SU:STO
, 90% of SMBCLK to 10% of
SMBDATA; V
CC
= 2.7V to 5.5V
t
SU:DAT
, 10% or 90% of SMBDATA to 10% of
SMBCLK; V
CC
= 2.7V to 5.5V
t
HD:DAT
, V
CC
= 2.7V to 5.5V
t
HD:DAT
, V
CC
= 2.7V to 5.5V
4.7
250
4
4
250
0
300
MIN
TYP
MAX
300
UNITS
ns
µs
ns
µs
µs
ns
µs
ns
MAX1755/MAX1756
ELECTRICAL CHARACTERISTICS
(V
CC
= +3.3V,
T
A
= -40°C to +125°C,
unless otherwise noted.) (Note 2)
PARAMETER
TEMPERATURE COMPARATOR AND POWER SUPPLY
DAC Resolution (Note 3)
Temperature Comparison Error
Temperature Hysteresis
Temperature Window
Supply Voltage Range
Operating Supply Current
SMBus INTERFACE
SMBus Output Low Sink Current
ALERT, OVERT
Output Low Sink Current
ALERT, OVERT
Output High Leakage Current
SMBDATA forced to 0.4V; V
CC
= 2.7V to 5.5V
Pin forced to 0.4V
Pin forced to 5.5V
6
6
1
mA
mA
µA
SMBus static, logic inputs forced to V
CC
or GND
With respect to temperature comparison
value (MAX1755)
Lower threshold with respect to temperature
comparison value (MAX1756)
Monotonicity guaranteed
2
-5
-4.5
-9
2.375
+5
-3.5
o
o
o
CONDITIONS
MIN
TYP
MAX
UNITS
C
C
C
-7
5.5
200
V
µA
Note 2:
Limits are 100% production tested at T
A
= +25°C. Limits over operating temperature are guaranteed by design.
Note 3:
Guaranteed, but not 100% tested.
Note 4:
The SMBus logic block is a static design that works with clock frequencies down to DC. While slow operation is possible,
it violates the 10kHz minimum clock frequency and SMBus specifications and may monopolize the bus.
_______________________________________________________________________________________
3
SOT23 Local Temperature Comparators
with SMBus Serial Interface
MAX1755/MAX1756
Typical Operating Characteristics
(V
CC
= +3.3V, T
A
= +25°C, unless otherwise noted.)
TRIP THRESHOLD ACCURACY PERCENTAGE
OF PARTS SAMPLED vs. ACCURACY
MAX1755/6 toc01
ACCURACY vs. TEMPERATURE SETTING
MAX1755/6 toc02
SUPPLY CURRENT
vs. TEMPERATURE
MAX1755/6 toc03
20
PERCENTAGE OF PARTS SAMPLED (%)
1.00
0.75
0.50
ACCURACY (°C)
0.25
0
-0.25
-0.50
-0.75
130
120
SUPPLY CURRENT (µA)
110
100
90
80
70
60
V
CC
= +2.375V
-50
-25
0
25
50
75
V
CC
= +3.3V
V
CC
= +5.5V
15
0
5
0
-1.00
-0.50
0
ACCURACY (°C)
0.50
1.00
1.00
-50
-25
0
25
50
75
100 125 150
TEMPERATURE (°C)
100 125 150
TEMPERATURE (°C)
SUPPLY CURRENT
vs. TEMPERATURE (STANDBY)
MAX1755/6 toc04
V
OL
vs. I
OL
200
T
A
= +125°C
160
V
OL
(mV)
120
T
A
= +25°C
80
T
A
= -40°C
40
MAX1755/6 toc05
1.9
1.7
SUPPLY CURRENT (µA)
1.5
1.3
1.1
0.9
0.7
0.5
-50
-25
0
25
50
75
V
CC
= +2.375V
V
CC
= +3.3V
V
CC
= +5.5V
0
0
2
4
6
8
I
OL
(mA)
10
12
14
16
100 125 150
TEMPERATURE (°C)
S0T23 THERMAL STEP RESPONSE
65
60
55
50
45
40
35
30
25
20
15
10
5
0
-2
MAX1755/6 toc06
STARTUP AND POWER-DOWN
MAX1755/6 toc07
TEMPERATURE (°C)
A
V
CC
= 3.3V
T
A
= +110°C
SOT23 IMMERSED IN +60°C
FLUORINERT BATH
-1
0
1
2
3
4
5
B
TIME (s)
A: V
CC
, 2V/div
B: OVERT, 2V/div
4ms/div
4
_______________________________________________________________________________________
SOT23 Local Temperature Comparators
with SMBus Serial Interface
Pin Description
PIN
1
2
3
4
NAME
ADD
SMBDATA
SMBCLK
OVERT
ALERT
V
CC
GND
SMBus Address-Select Pin. See Table 3.
SMBus Serial-Data Input/Output, Open Drain
SMBus Serial-Clock Input
Open-Drain Thermostat Output
(MAX1755 Only)
Open-Drain SMBus Alert (Interrupt) Output
(MAX1756 Only)
Supply Voltage Input, +2.375V to +5.5V. Bypass V
CC
to GND with a 0.1µF capacitor. If supply is
noisy, insert 100Ω resistor in series with this connection.
Ground
FUNCTION
MAX1755/MAX1756
5
6
Detailed Description
The MAX1755/MAX1756 are temperature comparators
designed to work in conjunction with an external µC or
other digital intelligence through an SMBus interface.
The µC is typically a power-management or keyboard
controller, which generates SMBus serial commands
from a GPIO port or through a dedicated SMBus inter-
face block.
Figure 1 illustrates the circuit blocks in the MAX1755/
MAX1756. The output of an analog temperature-to-volt-
age converter signal is compared to the temperature-
stable output of a serially programmed dual-output
digital-to-analog converter (DAC). Great care is taken in
the design to ensure that the thermal signal is propor-
tional to absolute temperature or PTAT. A precision
comparator with low-input offset voltage is used to
compare the PTAT voltage to the DAC output.
The DAC provides two levels: one is set to the rising trip
threshold and the other is set to the falling threshold
(hysteresis) level by a digital subtractor. This arrange-
ment makes the hysteresis value very accurate with
respect to the rising trip point. Each DAC level is alter-
nately compared to the PTAT voltage through a sam-
pling system that reuses the same comparator, thereby
reducing errors due to comparator offset. The sampling
rate is typically 1kHz.
A simplified SMBus interface enables the system to
program the temperature thresholds and read the part’s
status register.
SMBus Digital Interface
The SMBus block utilizes the read-byte/write-byte pro-
tocol. It only supports 8-bit reads and writes, has no
command byte, and does not need to support the Alert
Response feature. From a software perspective, the
MAX1755/MAX1756 appear as write registers contain-
ing the DAC comparison value and as read registers
containing the status byte. A standard SMBus 2-wire
serial interface is used to program DAC values and
read the status byte. Figure 2 shows the SMBus data
protocols and Figure 3 details the SMBus timing.
Programming the T
MAX
Register
The T
MAX
register is programmed using a standard
SMBus Send Byte operation. The temperature data for-
mat is 6 bits plus sign in two’s complement form, with
each data bit representing 2°C (Table 1). The MSB is
transmitted first, LSB last. The MSB (B7) of the T
MAX
register is an embedded control bit, which can either
invert the polarity of the
OVERT
output (MAX1755) or
mask low-going (T
HYST
) interrupts (MAX1756). The B6
bit of the T
MAX
register is the sign bit for the remaining
6 bits that make up the binary-coded temperature
threshold.
Software Standby Mode
If the DAC code is set to negative full scale, the device
goes into software standby mode. In standby mode,
supply current is reduced to 0.8µA. At very low supply
voltages (UVLO threshold), the supply current is higher
due to address decoding. Typical supply current can
be as high as 250µA, depending on the ADD setting,
while the typical ADD input current can be as high as
40µA. Exiting standby mode causes the slave address
to be checked again.
_______________________________________________________________________________________
5
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