19-2458; Rev 0; 10/02
PWM Output Temperature Sensors
in SC70 Packages
General Description
The MAX6672/MAX6673 are low-current temperature
sensors with a single-wire output. These temperature
sensors convert the ambient temperature into a 1.4kHz
PWM output, which contains the temperature informa-
tion in its duty cycle. The MAX6672 has an open-drain
output and the MAX6673 has a push-pull output.
The MAX6672/MAX6673 operate from 2.4V to 5.5V with
a maximum supply current of 150µA. Both devices fea-
ture a single-wire output that minimizes the number of
pins necessary to interface with a microprocessor.
The MAX6672/MAX6673 are available in 5-pin SC70
packages.
o
Simple Single-Wire PWM Output
o
Tiny SC70 Package
o
Low 60µA (typ) Supply Current Consumption
o
1.4kHz Nominal Frequency
o
Choice of Outputs
Open Drain (MAX6672)
Push-Pull (MAX6673)
o
2.4V to 5.5V Supply Range
Features
MAX6672/MAX6673
Applications
Industrial and Process Control
HVAC
Automotive
Environmental Control
Isolated Temperature Sensing
PART
Ordering Information
TEMP RANGE
PIN-
PACKAGE
5 SC70-5
5 SC70-5
TOP
MARK
ACQ
ACR
MAX6672AX
K-T -40°C to +125°C
MAX6673AX
K-T -40°C to +125°C
Typical Application Circuit
Pin Configuration
µC
V
CC
*
0.1µF
MAX6672
MAX6673
GND
GPIO TO CONTROL
SHUTDOWN
INPUT TO TIMER/
COUNTER
TOP VIEW
DOUT
1
5
V
CC
N.C.
2
MAX6672
MAX6673
4
GND
GND
3
SC70
* PULLUP RESISTOR REQUIRED ONLY FOR THE MAX6672.
________________________________________________________________
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.
PWM Output Temperature Sensors
in SC70 Packages
MAX6672/MAX6673
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (V
CC
to GND) ................................. -0.3V to +6V
DOUT to GND (MAX6672)........................................-0.3V to +6V
DOUT to GND (MAX6673)..........................-0.3V to (V
CC
+ 0.3V)
DOUT Short to GND ...................................................Continuous
ESD Protection (Human Body Model) ............................ ±2000V
Continuous Power Dissipation (T
A
= +70°C)
5-Pin SC70 (derate 2.5mW/°C above +70°C). ............200mW
Operating Temperature Range .........................-40°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature ......................................................+150°C
SC70 Package
Vapor Phase (60s) ...................................................... +215°C
Infrared (15s). ............................................................. +220°C
Lead Temperature (soldering, 10s) ................................ +300°C
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
= 2.4V to 5.5V, T
A
= -40°C to +125°C, unless otherwise noted. Typical values specified at +25°C and V
CC
of 3.3V.) (Note 1)
PARAMETER
Temperature Error
(Note 2)
Nominal t
1
Pulse Width
Output Low Voltage
Output High Voltage
Fall Time
Rise Time
DOUT Open-Drain Leakage
Current
Output Capacitance
Power-Supply Rejection Ratio
Supply Current
PSRR
I
CC
2.4V to 5.5V, T
A
= -25°C to +125°C
2.4V to 3.6V
3.6V to 5.5V
V
OL
V
OH
t
FALL
t
RISE
I
SINK
= 3mA
I
SOURCE
= 800µA (MAX6673)
C
LOAD
= 100pF
C
LOAD
= 100pF (MAX6673)
V
DOUT
= 6V (MAX6672)
V
CC
- 0.5
14
96
0.1
2.5
0.3
60
70
0.8
100
150
SYMBOL
CONDITIONS
T
A
= +25°C to +100°C
V
CC
= 3.3V
T
A
= 0°C to +125°C
T
A
= -20°C to +125°C
T
A
= -40°C to -20°C
MIN
-3
-4
-5
±3
280
0.4
µs
V
V
ns
ns
µA
pF
°C/V
µA
TYP
MAX
+3
+4
+5
°C
UNITS
Note 1:
All specifications are 100% tested at T
A
= +25°C. Specification limits over temperature (T
A
= -40°C to +125°C) are guaranteed
by design, not production tested.
Note 2:
Temperature = -200
✕
(0.85 - T
1
/T
2
)
3
+ (425
✕
T
1
/T
2
) - 273. T
1
is the low time period. T
2
is the high time period (Figure 1).
2
_______________________________________________________________________________________
PWM Output Temperature Sensors
in SC70 Packages
Typical Operating Characteristics
(V
CC
= 3.3V, T
A
= +25°C, unless otherwise noted.)
NORMALIZED OUTPUT FREQUENCY
vs. SUPPLY VOLTAGE
MAX6672 toc02
MAX6672/MAX6673
OUTPUT FREQUENCY vs. TEMPERATURE
MAX6672 toc01
t
1
AND t
2
TIMES vs. TEMPERATURE
MAX6672 toc03
2.00
1.010
NORMALIZED FREQUENCY (kHz)
600
T
A
= +125°C
1.000
T
A
= +25°C
0.995
T
A
= -40°C
t
1
AND t
2
TIMES (µs)
1.75
FREQUENCY (kHz)
1.005
500
t
2
400
1.50
1.25
300
t
1
200
1.00
-50
-25
0
25
50
75
100
125
TEMPERATURE (°C)
0.990
2.0
2.5
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
-50
-25
0
25
50
75
100
125
TEMPERATURE (°C)
OUTPUT ACCURACY vs. TEMPERATURE
MAX6672 toc04
SUPPLY CURRENT vs. TEMPERATURE
MAX6672 toc05
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX6672 toc06
4
V
CC
= 3.3V
150
100
SUPPLY CURRENT (µA)
90
V
CC
= 5V
60
V
CC
= 3.3V
30
SUPPLY CURRENT (µA)
75
100
125
2
ACCURACY (°C)
120
90
80
0
70
-2
60
-4
-50
-25
0
25
50
75
100
125
TEMPERATURE (°C)
0
-50
-25
0
25
50
TEMPERATURE (°C)
50
2.0
2.5
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
POWER-SUPPLY REJECTION
vs. TEMPERATURE
MAX6672 toc07
POWER-SUPPLY REJECTION
vs. FREQUENCY
MAX6672 toc08
OUTPUT RISE AND FALL TIMES
vs. CAPACITIVE LOAD
MAX6672 toc09
1.0
POWER-SUPPLY REJECTION (°C/V)
1.0
POWER-SUPPLY REJECTION (°C/V)
150
OUTPUT RISE AND FALL TIMES (ns)
0.5
0.5
120
90
MAX6673 RISE TIME
60
0
0
-0.5
-0.5
V
AC
= 100mV
P-P
30
FALL TIME
0
-1.0
-50
-25
0
25
50
75
100
125
TEMPERATURE (°C)
-1.0
0.01
0.10
1
10
100
1k
10k
FREQUENCY (Hz)
0.01
0.10
1
10
CAPACITIVE LOAD (nF)
_______________________________________________________________________________________
3
PWM Output Temperature Sensors
in SC70 Packages
MAX6672/MAX6673
Typical Operating Characteristics (continued)
(V
CC
= 3.3V, T
A
= +25°C, unless otherwise noted.)
THERMAL RESPONSE
IN STIRRED OIL BATH
MAX6672 toc10
OUTPUT SINK CURRENT
vs. TEMPERATURE
MAX6672 toc11
MAX6673 OUTPUT SOURCE CURRENT
vs. TEMPERATURE
V
OH
= V
CC
- 0.5V
MAX6672 toc12
100
30
25
SINK CURRENT (mA)
20
15
V
OL
= 0.4V
3.0
2.5
SOURCE CURRENT (mA)
2.0
TEMPERATURE (°C)
75
V
CC
= 5V
V
CC
= 5V
1.5
1.0
0.5
0
V
CC
= 3.3V
V
CC
= 3.3V
10
5
0
50
TRANSITION FROM +25°C AIR
TO +100°C STIRRED OIL BATH
25
0
4
8
12
TIME (s)
16
20
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
100
125
TEMPERATURE (°C)
TEMPERATURE (°C)
Pin Description
PIN
1
2
3, 4
5
NAME
DOUT
N.C.
GND
V
CC
No Connection. Not internally connected.
Pin 3 and Pin 4 must be tied together and connected to ground.
Positive Supply. Bypass with a 0.1µF capacitor to GND.
FUNCTION
Digital Output Pin. PWM output, open-drain output (MAX6672), or push-pull output (MAX6673).
Detailed Description
The MAX6672/MAX6673 are low-current (60µA, typ),
local temperature sensors ideal for interfacing with µCs
or µPs. The MAX6672/MAX6673 convert their own tem-
perature into a ratiometric PWM output. The square-
wave output waveform time ratio contains the
temperature information. The output is a square wave
with a nominal frequency of 1.4kHz at +25°C. The tem-
perature is obtained with the following formula:
Temperature (°C) = -200 x (0.85 - t
1
/ t
2
)
3
+ (425 x t
1
/ t
2
) - 273
Where t
1
is a fixed value and t
2
is modulated with the
temperature. Table 1 lists time ratio vs. temperature.
For temperatures greater than +50°C, the temperature
error is primarily first order and the following equation
can be used:
Temperature (°C) = (425 x t
1
/ t
2
) - 273
The MAX6673 has a push-pull output. The rise and fall
times of the MAX6673 output are negligible with
respect to the period; therefore, errors caused by
capacitive loading are minimized.
The output load capacitance should be minimized in
MAX6672 applications because the sourcing current is
set by the pullup resistor. If the output capacitance
becomes too large, unequal rise and fall times distort
the pulse width, thus delivering inaccurate readings.
Applications Information
Pulse-Width Modulation
Interfacing with a µC
The
Typical Application Circuit
shows the MAX6672/
MAX6673 interfaced with a µC. In this example, the
MAX6672/MAX6673 convert the ambient temperature
to a PWM waveform. The µC reads the temperature by
measuring the t
1
and t
2
periods in software and hard-
ware. The only timing requirements are that the clock
frequency used for timing measurements is stable and
4
_______________________________________________________________________________________
PWM Output Temperature Sensors
in SC70 Packages
Table 1. Time Ratio vs. Temperature
TIME RATIO
(t
1
/t
2
)
0.936
0.878
0.807
0.714
0.646
0.602
0.560
TEMPERATURE
(°C)
125
100
70
30
0
-25
-40
5
V
CC
MAX6672/MAX6673
t
2
t
1
Figure 1. PWM Waveform Timing
Block Diagram
high enough to provide the required measurement res-
olution. The interface for the MAX6672 requires a pullup
resistor.
Thermal Response Time
The time periods t
1
(low) and t
2
(high) are values that
are easily read by the µP timer/counter. The tempera-
ture reading is then calculated using software. Since
both periods are obtained consecutively, using the
same clock, performing the division indicated in the
above formulae results in a ratiometric value that is
independent of the exact frequency.
TEMPERATURE
SENSOR
PWM
MODULATOR
DOUT 1
t
2
GND
3, 4
t
1
Sensing Circuit Board and Ambient
Temperatures
Temperature sensor ICs such as the MAX6672/
MAX6673 that sense their own die temperatures must
be mounted on or close to the object whose tempera-
ture they are intended to measure. Because there is a
good thermal path between the SC70 package’s metal
leads and the IC die, the MAX6672/MAX6673 can
accurately measure the temperature of the circuit
board to which they are soldered. If the sensor is
intended to measure the temperature of a heat-generat-
ing component on the circuit board, it should be mount-
ed as close as possible to that component and should
share supply and ground traces (if they are not noisy)
with that component where possible. This maximizes
the heat transfer from the component to the sensor.
The thermal path between the plastic package and the
die is not as good as the path through the leads, so the
MAX6672/MAX6673, like all temperature sensors in
plastic packages, are less sensitive to the temperature
of the surrounding air than they are to the temperature
of their leads. They can be successfully used to sense
ambient temperature if the circuit board is designed to
track the ambient temperature.
As with any IC, the wiring and circuits must be kept
insulated and dry to avoid leakage and corrosion,
especially if the part is operated at cold temperatures
where condensation can occur.
The error caused by power dissipation in the MAX6672/
MAX6673 is negligible.
Chip Information
TRANSISTOR COUNT: 601
PROCESS: BiCMOS
_______________________________________________________________________________________
5
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