General Description
The MAX6676/MAX6677 are high-accuracy, low-power
temperature sensors with a single-wire output. The
MAX6676/MAX6677 convert the ambient temperature
into a ratiometric PWM output with temperature information contained in the duty cycle of the output square
wave. The MAX6676 has an open-drain output and the
MAX6677 has a push-pull output.
The MAX6676/MAX6677 are specified for operation
with power-supply voltages from 1.8V to 3.6V, or from
3.6V to 5.5V. The typical unloaded supply current is
80µA. All 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 1.8kHz (±20%) at +25°C. The
output format is decoded as follows:
Temperature (°C) = 398.15 ✕(t1/ t2) - 273.15
Where t1is fixed with a typical value of 0.24ms and t2is
modulated by the temperature. The MAX6676/
MAX6677 operate from -40°C to +125°C and are available in space-saving 6-pin SOT23 packages.
Applications
Process Control
Industrial
HVAC and Environmental Control
Automotive
Portable Devices
µP and µC Temperature Monitoring
Isolated Temperature Sensing
Features
♦ Simple Single-Wire, 1.8kHz PWM Output
♦ Operates Down to 1.8V
♦ High Accuracy
±1.5°C at TA= +25°C
±3.0°C at TA= 0°C to +85°C
♦ Operates from -40°C to +125°C
♦ Low 80µA Typical Current Consumption
♦ Small 6-Pin SOT23 Package
MAX6676/MAX6677
Low-Voltage, 1.8kHz PWM Output Temperature
Sensors
________________________________________________________________ Maxim Integrated Products 1
Pin Configuration
Ordering Information
V
CC
V
CC
*REQUIRED ONLY FOR MAX6676.
5.1kΩ*
GND
DOUT
µC
INPUT TO
TIMER/COUNTER
MAX6676
t
2
t
1
0.1µF
Typical Operating Circuit
19-2660; Rev 0; 10/02
*Future product—contact factory for availability.
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.
Selector Guide
PART
MAX6676AUT3-T -40°C to +125°C 6 SOT23-6
MAX6676AUT5-T* -40°C to +125°C 6 SOT23-6
MAX6677AUT3-T* -40°C to +125°C 6 SOT23-6
MAX6677AUT5-T* -40°C to +125°C 6 SOT23-6
TEMP
RANGE
PART
MAX6676AUT3 Open drain 1.8 to 3.6 ABBF
MAX6676AUT5 Open drain 3.6 to 5.5 ABBG
MAX6677AUT3 Push-pull 1.8 to 3.6 ABBH
MAX6677AUT5 Push-pull 3.6 to 5.5 ABBI
OUTPUT
TYPE
PINPACKAGE
SUPPLY
VOLTAGE
RANGE (V)
MARK
TOP
TOP VIEW
16GND
DOUT
GND
2
34
CC
MAX6676
MAX6677
SOT23
5 GND
GNDV
MAX6676/MAX6677
Low-Voltage, 1.8kHz PWM Output Temperature
Sensors
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC= 1.8V to 3.6V (MAX6676AUT3/MAX6677AUT3), VCC= 3.6V to 5.5V (MAX6676AUT5/MAX6677AUT5), TA= -40°C to +125°C, unless
otherwise noted. Typical values are at V
CC
= 3.0V (MAX6676AUT3/MAX6677AUT3), VCC= 5.0V (MAX6676AUT5/MAX6677AUT5),
T
A
= +25°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.
Note 1: Parts are tested at +25°C. Specifications are guaranteed by design over temperature.
(Voltages Referenced to GND)
V
CC
........................................................................-0.3V to +6.0V
DOUT (MAX6676)..................................................-0.3V to +6.0V
DOUT (MAX6677).......................................-0.3V to (V
CC
+ 0.3V)
DOUT Current .....................................................-1mA to +50mA
ESD Protection (DOUT, Human Body Model) .................±2000V
Continuous Power Dissipation (T
A
= +70°C)
6-Pin SOT23 (derate 8.7mW/°C above +70°C).........695.7mW
Operating Temperature Range .........................-40°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
Supply Voltage Range V
Supply Current I
Temperature Error
Nominal t1 Pulse Width 240 µs
Output High Voltage V
Output Leakage Current V
Output Low Voltage V
Fall Time t
Rise Time t
Digital Output Capacitance C
Power-Supply Rejection Ratio PSRR VCC = 1.8V - 3.6V -1.2 +0.4 +1.2 °C/V
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX6676AUT3/MAX6677AUT3 1.8 3.6
CC
MAX6676AUT5/MAX6677AUT5 3.6 5.5
CC
OUT
RL = ∞ 80 200 µA
TA = +25°C
T
= 0°C to +85°C
A
T
= -20°C to +100°C -4.2 +4.2
A
= -40°C to +125°C
T
A
IOH = 800µA, MAX6677
OH
= VCC, MAX6676 0.1 µA
OUT
IOL = 3mA 0.5 V
OL
CL = 100pF, RL = 10kΩ 20 ns
F
MAX6676, CL = 15pF, RL = 10kΩ 300 ns
R
-1.5 +1.5
-3.0 +3.0
-5.5 +5.5
V
-
CC
0.5
15 pF
V
°C
V
MAX6676/MAX6677
Low-Voltage, 1.8kHz PWM Output Temperature
Sensors
_______________________________________________________________________________________ 3
Typical Operating Characteristics
(VCC= 3.0V, TA= +25°C, unless otherwise noted.)
MAX6676 toc09
V
OUT
10ns/div
0V
OUTPUT FALL TIME
(C
L
= 100pF, RL = 100kΩ)
OUTPUT ACCURACY
vs. TEMPERATURE
MAX6676 toc04
TEMPERATURE (°C)
OUTPUT ACCURACY (°C)
85603510-15
-3
-1
1
3
5
-5
-40
110
OUTPUT FREQUENCY
vs. TEMPERATURE
3.0
2.5
2.0
OUTPUT FREQUENCY (kHz)
1.5
1.0
-40 110
TEMPERATURE (°C)
85603510-15
2.50
MAX6676 toc01
2.25
2.00
OUTPUT FREQUENCY (Hz)
1.75
1.50
600
500
400
300
200
SUPPLY CURRENT (µA)
100
MAX6676AUT3 OUTPUT FREQUENCY
vs. SUPPLY VOLTAGE
TEMP = +125°C
TEMP = +25°C
TEMP = -40°C
1.8 3.6
SUPPLY VOLTAGE (V)
MAX6676AUT3 SUPPLY CURRENT
vs. TEMPERATURE
VCC = 3.6V
VCC = 3.0V
VCC = 1.8V
0
-40 110
5.1kΩ PULLUP RESISTOR
TEMPERATURE (°C)
3.33.02.72.42.1
85603510-15
MAX6676 toc02
MAX6676 toc05
t1 AND t2 TIMES
vs. TEMPERATURE
450
t
2
400
350
TIME (µs)
300
t
250
1
200
-40 110
TEMPERATURE (°C)
MAX6676AUT3 SUPPLY CURRENT
vs. SUPPLY VOLTAGE
450
400
350
300
250
5.1kΩ PULLUP
200
150
SUPPLY CURRENT (µA)
100
NO PULLUP
50
0
1.8 3.6
SUPPLY VOLTAGE (V)
MAX6676 toc03
85603510-15
MAX6676 toc06
3.33.02.72.42.1
POWER-SUPPLY REJECTION RATIO
vs. TEMPERATURE
1.0
0.5
0
PSRR (°C/V)
-0.5
-1.0
-50
TEMPERATURE (°C)
MAX6676 toc07
100 1257550250-25
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
2
1
0
-1
-2
-3
-4
CHANGE IN TEMPERATURE (°C)
-5
VAC = 100mV
-6
1 10k
P-P
10010
FREQUENCY (Hz)
MAX6676 toc08
1k
MAX6676/MAX6677
Low-Voltage, 1.8kHz PWM Output Temperature
Sensors
4 _______________________________________________________________________________________
Detailed Description
The MAX6676/MAX6677 are high-accuracy, low-current
(80µA, typ) temperature sensors ideal for interfacing
with µCs or µPs. The MAX6676/MAX6677 convert the
ambient temperature into a ratiometric PWM output at a
nominal frequency of 1.8kHz (±20%) at +25°C.
The time periods, t1(low) and t2(high) (Figure 1), are
easily read by a µP’s timer/counter port. To calculate
the temperature, use the following expression:
Temperature (°C) = 398.15 x (t1/ t2) - 273.15
The µC or µP measures the output of the MAX6676/
MAX6677 by counting t1and t2and 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. Always use the same
clock for t1and t2counters so that the temperature is
strictly based on a ratio of the two times, thus eliminating errors due to different clocks’ frequencies.
The MAX6677 (Figure 2a) has a push-pull output with
full CMOS output swings. The ability to source and sink
current allows the MAX6677 to drive capacitive loads
up to 100pF with less than 1°C error.
The MAX6676 (Figure 2b) has an open-drain output.
The output capacitance should be minimized in
MAX6676 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.
Applications Information
Accurate temperature monitoring requires a good thermal contact between the MAX6676/MAX6677 and the
object being monitored. A precise temperature measurement depends on the thermal resistance between
the object being monitored and the MAX6676/
MAX6677 die. Heat flows in and out of plastic packages primarily through the leads. If the sensor is intended to measure the temperature of a heat-generating
component 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.
Power Supply from µP Port Pin
The low quiescent current of the MAX6676/MAX6677
enables them to be powered from a logic line, which
meets the requirements for supply voltage range. This
provides 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.
Pin Description
Figure 1. MAX6676/MAX6677 PWM Output
Figure 2. Output Configurations
PIN NAME FUNCTION
1 DOUT
2, 4, 5, 6 GND
3V
CC
Digital Output Pin. The duty
cycle of the output waveform is
modulated by temperature.
Ground. All four ground pins
must be connected to GND.
Supply Voltage. It is
recommended bypassing V
to GND with a 0.1µF capacitor.
CC
t
2
t
1
V
CC
P
DOUT
N
(a) (b)
V
CC
DOUT
N
MAX6677
MAX6676
MAX6676/MAX6677
Low-Voltage, 1.8kHz PWM Output Temperature
Sensors
_______________________________________________________________________________________ 5
Galvanic Isolation
Use an optocoupler to isolate the MAX6676/MAX6677
whenever a high common-mode voltage is present.
Choose an optocoupler with equal turn-on and turn-off
times. Unequal turn-on/turn-off times produce an error
in the temperature reading (Figure 3).
Thermal Considerations
Self-heating may cause the temperature measurement
accuracy of the MAX6676/MAX6677 to degrade in
some applications. The quiescent dissipation and the
power dissipated by the digital output may cause
errors in obtaining the accurate temperature measurement. The temperature errors depend on the thermal
conductivity of the package (SOT23, +140°C/W), the
mounting technique, and the airflow. Static dissipation
is typically 4.0µW operating at 5V with no load. For
example, an out load of 3mA creates a maximum error
of less than 0.1°C.
Multiple Logic Voltages
Use the MAX6676 open-drain output to drive devices
operating at supply voltages other than the MAX6676’s
VCC. As shown in Figure 4, connect a pullup resistor
from the other supply voltage to the MAX6676 output.
Limit the resistor’s current to less than 1mA, thus maintaining an output low logic level of less than 200mV.
Chip Information
TRANSISTOR COUNT: 2096
PROCESS: BiCMOS
Figure 3. Galvanic Isolation Using an Optocoupler
Figure 4. Low-Voltage Logic
3.3V
MAX6676AUT3
DOUT
V
ISO
V
V
CC
MAX6676
DOUT
5.1kΩ
DD
MAX6676/MAX6677
Low-Voltage, 1.8kHz PWM Output Temperature
Sensors
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
6 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
6LSOT.EPS
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