19-2138; Rev 3; 8/09
High-Accuracy PWM Output Temperature
Sensors
General Description
The MAX6666/MAX6667 are high-accuracy, low-cost,
low-power temperature sensors with a single-wire
output. The MAX6666/MAX6667 convert the ambient
temperature into a ratiometric PWM output with temper-
ature information contained in the duty cycle of the out-
put square wave. The MAX6666 has a push-pull output
and the MAX6667 has an open-drain output.
The MAX6666/MAX6667 operate at supply voltages
from +3V to +5.5V. The typical unloaded supply current
at 5.0V is 200µA. Both devices feature a single-wire
output that minimizes the number of pins necessary to
interface with a microprocessor (µP). The output is a
square wave with a nominal frequency of 35Hz (±20%)
at +25°C. The output format is decoded as follows:
Temperature (°C) = 235 - (400 x t
1
) / t
2
Where t
1
is fixed with a typical value of 10ms and t
2
is
modulated by the temperature (Figure 1). The MAX6666/
MAX6667 operate from -40°C to +125°C and are available
in space-saving SOT23 packages.
o
Simple Single-Wire PWM Output
o
±1.0°C Accuracy at +25°C
o
High Accuracy
±1°C at T
A
= +30°C
±2.5°C at T
A
= +10°C to +50°C
o
Operate Up to +125°C
o
Low 200µA Typical Current Consumption
o
Small SOT23 package
Features
MAX6666/MAX6667
Applications
Process Control
Industrial
HVAC and Environmental Control
Automotive
µP and µC Temperature Monitoring
PART
MAX6666AUT+T
MAX6667AUT+T
Ordering Information
TEMP RANGE
-40°C to +125°C
-40°C to +125°C
PIN-
PACKAGE
6 SOT23
6 SOT23
TOP
MARK
AATF
AATG
+Denotes
a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
Typical Operating Circuit
TOP VIEW
t
1
t
2
Pin Configuration
+3.3V
V
CC
+
D
OUT
µC
INPUT TO
TIMER/COUNTER
1
MAX6666
MAX6667
6
I.C.
MAX6666
MAX6667
DOUT
GND
V
CC
2
5
I.C.
GND 3
4
I.C.
SOT23
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
High-Accuracy PWM Output Temperature
Sensors
MAX6666/MAX6667
ABSOLUTE MAXIMUM RATINGS
(Voltages Referenced to GND)
V
CC
........................................................................-0.3V to +6.0V
D
OUT
MAX6666................................................-0.3V to (V
CC
+ 0.3V)
MAX6667 ..........................................................-0.3V to + 6.0V
D
OUT
Current ......................................................-1mA to +50mA
Continuous Current into Any Other Terminal....................±20mA
Continuous Power Dissipation (T
A
= +70°C)
6-Pin SOT23 (derate 7.4mW/°C above +70°C)............595mW
Operating Temperature Range .........................-40°C to +150°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature ......................................................+150°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
= +3.0V to +5.5V, T
A
= -40°C to +125°C, unless otherwise noted. Typical values are at V
CC
= +3.3V, T
A
= +25°C.)
PARAMETER
Supply Voltage Range
Supply Current
SYMBOL
V
CC
I
CC
V
CC
= +3.0V to +5.5V
T
A
= +30°C
T
A
= +10°C to +50°C
Temperature Error
V
CC
= +3.3V
T
A
= 0°C to +100°C
T
A
= -25°C to +125°C
T
A
= -40°C, V
CC
= +3.3V
Nominal t
1
Pulse Width
MAX6666 Output High Voltage
MAX6666 Output Low Voltage
MAX6666 Fall Time
MAX6666 Rise Time
MAX6667 Output Low Voltage
MAX6667 Fall Time
MAX6667 Output Capacitance
MAX6667 Output Leakage
Power-Supply Rejection Ratio
PSRR
V
CC
= +3.0V to +5.5V
I
OH
= 800µA
I
OL
= 800µA
C
L
= 100pF, R
L
=
∞
C
L
= 100pF, R
L
=
∞
I
SINK
= 1.6mA
I
SINK
= 5.0mA
C
L
= 100pF, R
L
= 10kΩ
C
L
= 0
40
15
<0.1
0.3
1.0
80
80
0.4
1.2
V
CC
- 0.4
0.4
-1
-2.5
-3.8
-4.8
-6
10
CONDITIONS
MIN
3.0
200
TYP
MAX
5.5
500
+1
+2.5
+3.8
+4.8
+6
ms
V
V
ns
ns
V
ns
pF
µA
°C/V
°C
UNITS
V
µA
2
_______________________________________________________________________________________
High-Accuracy PWM Output Temperature
Sensors
Detailed Description
The MAX6666/MAX6667 are high-accuracy, low-cost,
low current (200µA typ) temperature sensors ideal for
interfacing with µCs or µPs. The MAX6666/MAX6667
convert the ambient temperature into a ratiometric
PWM output at a nominal frequency of 35Hz (±20%) at
+25°C.
The time periods, t
1
(high) and t
2
(low) (Figure 1), are
easily read by the µP’s timer/counter port. To calculate
the temperature, use the expression below:
Temperature (°C) = +235 - (400 x t
1
) / t
2
The µC or µP measures the output of the MAX6666/
MAX6667 by counting t
1
and t
2
and computing the
temperature based on their ratio. The resolution of the
count is a function of the processor clock frequency
and the resolution of the counter. The MAX6666/
MAX6667 have a resolution of approximately 11 bits.
Always use the same clock for t
1
and t
2
counters so
that the temperature is strictly based on a ratio of the
two times, thus eliminating errors due to different
clocks’ frequencies.
The MAX6666 (Figure 2a) has a push-pull output and
provides rail-to-rail output drive. The ability to source
and sink current allows the MAX6666 to drive capaci-
tive loads up to 10nF with less than 1°C error.
The MAX6667 (Figure 2b) has an open-drain output.
The output capacitance should be minimized in
MAX6667 applications because the sourcing current is
set by the pullup resistor. If the output capacitance
becomes too large, lengthy rise and fall times distort
the pulse width, resulting in inaccurate measurements.
t
1
MAX6666/MAX6667
t
2
Figure 1. MAX6666/MAX6667 PWM Output
Power-Supply Bypassing
The MAX6666/MAX6667 operate from a +3V to +5.5V
supply. If a noisy power-supply line is used, bypass
V
CC
to GND with a 0.1µF capacitor.
Power Supply from µP Port Pin
The low quiescent current of the MAX6666/MAX6667
enables it to be powered from a logic line, which meets
the requirements for supply voltage range. This pro-
vides a simple shutdown function to totally eliminate
quiescent current by taking the logic line low. The logic
line must be able to withstand the 0.1µF power-supply
bypass capacitance.
Galvanic Isolation
Use an optocoupler to isolate the MAX6666/MAX6667
whenever a high common-mode voltage is present.
Because some optocouplers have turn-off times that
are much longer than their turn-on times, choose an
optocoupler with equal turn-on and turn-off times.
Unequal turn-on/turn-off times produce an error in the
temperature reading.
Applications Information
Accurate temperature monitoring requires a good ther-
mal contact between the MAX6666/MAX6667 and the
object being monitored. A precise temperature mea-
surement depends on the thermal resistance between
the object being monitored and the MAX6666 die. Heat
flows in and out of plastic packages primarily through
the leads. For the best thermal contact, connect all
unused pins to ground. If the sensor is intended to
measure the temperature of a heat-generating compo-
nent on the circuit board, mount the device as close as
possible to that component and share the ground
traces (if they are not too noisy) with the component.
This maximizes the heat transfer from the component to
the sensor.
Thermal Considerations
Self-heating may cause the temperature measurement
accuracy of the MAX6666/MAX6667 to degrade in
some applications. The quiescent dissipation and the
power dissipated by the digital output may cause
errors in obtaining the accurate temperature measure-
ment. The temperature errors depend on the thermal
conductivity of the package (SOT23, 140°C/W), the
mounting technique, and the airflow. Static dissipation
in the MAX6666/MAX6667 is typically 4.5mW operating
at 5V with no load. As a worst-case example, consider
the MAX6667 and its maximum rated load of 5mA and
assume a maximum output voltage of 0.8V adds 4mW
power dissipation. Use Figure 3 to estimate the temper-
ature error.
_______________________________________________________________________________________
5
Embedded System
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