MAX6642ATT90+T Maxim Integrated Products, MAX6642ATT90+T Datasheet - Page 12

• Manufacturer Part Number: MAX6642ATT90+T
• Description: IC TEMP SENSOR SMBUS 6-TDFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX6642ATT90+T

• Function: Temp Monitoring System (Sensor)
• Topology: ADC, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, 0°C ~ 150°C
• Output Type: I²C™/SMBus™
• Output Alarm: Yes
• Output Fan: No
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 6-TDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: MAX6642ATT90+T; MAX6642ATT90+TTR

Cable resistance also affects remote-sensor accuracy.
For every 1Ω of series resistance, the error is approxi-
mately 1/2°C.
When sensing local temperature, this device is intend-
ed to measure the temperature of the PCB to which it is
soldered. The leads provide a good thermal path
between the PCB traces and the die. Thermal conduc-
tivity between the die and the ambient air is poor by
comparison, making air temperature measurements
impractical. Because the thermal mass of the PCB is far
greater than that of the MAX6642, the device follows
temperature changes on the PCB with little or no per-
ceivable delay.
When measuring temperature of a CPU or other IC with
an on-chip sense junction, thermal mass has virtually
no effect; the measured temperature of the junction
tracks the actual temperature within a conversion cycle.
When measuring temperature with discrete remote sen-
sors, smaller packages, such as SOT23s, yield the best
thermal response times. Take care to account for ther-
mal gradients between the heat source and the sensor,
and ensure that stray air currents across the sensor
package do not interfere with measurement accuracy.
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
12
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Thermal Mass and Self-Heating
Self-heating does not significantly affect measurement
accuracy. Remote-sensor self-heating due to the diode
current source is negligible. For the local diode, the
worst-case error occurs when autoconverting at the
fastest rate and simultaneously sinking maximum cur-
rent at the ALERT output. For example, with V
+5.0V, at an 8Hz conversion rate and with ALERT sink-
ing 1mA, the typical power dissipation is:
ø
assuming no copper PCB heat sinking, the resulting
temperature rise is:
Even under nearly worst-case conditions, it is difficult to
introduce a significant self-heating error.
J-A
for the 6-pin TDFN package is about +41°C/W, so
5.0V x 450µA + 0.4V x 1mA = 2.65mW
ΔT = 2.65mW x 41°C/W = +0.11°C
CC
=