MAX6680MEE+T Maxim Integrated Products, MAX6680MEE+T Datasheet - Page 7

• Manufacturer Part Number: MAX6680MEE+T
• Description: IC TEMP SENSOR SMBUS 16-QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX6680MEE+T

• Function: Thermometer, Thermostat
• Topology: ADC, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -55°C ~ 125°C, External Sensor
• Output Type: I²C™/SMBus™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -55°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Full Temp Accuracy: +/- 5 C, +/- 3 C
• Digital Output - Bus Interface: Serial (2-Wire)
• Digital Output - Number Of Bits: 10 bit + Sign
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 55 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

age and computes the temperature based on this volt-
age. If the remote channel is not used, connect DXP to
DXN. Do not leave DXP and DXN unconnected.
When a conversion is initiated, both channels are con-
verted whether or not they are used. The DXN input is
biased at one V
to set up the ADC inputs for a differential measurement.
Resistance in series with the remote diode causes
about 1/2°C error per ohm.
A conversion sequence consists of a local temperature
measurement and a remote temperature measurement.
Each time a conversion begins, whether initiated auto-
matically in the free-running autoconvert mode
(RUN/STOP = 0) or by writing a One-Shot command,
both channels are converted, and the results of both
measurements are available after the end of conver-
sion. A BUSY status bit in the Status register shows that
the device is actually performing a new conversion. The
results of the previous conversion sequence are still
available when the ADC is busy.
The MAX6680/MAX6681 can directly measure the die
temperature of CPUs and other ICs that have on-board
temperature-sensing diodes (see the Typical Operating
Circuit) or they can measure the temperature of a dis-
crete diode-connected transistor. The type of remote
diode used is set by bit 5 of the Configuration Byte. If
bit 5 is set to zero, the remote sensor is a diode-con-
nected transistor, and if bit 5 is set to 1, the remote sen-
sor is a substrate or common-collector PNP transistor.
For best accuracy, the discrete transistor should be a
small-signal device with its collector and base connect-
ed together. Accuracy has been experimentally verified
for all of the devices listed in Table 1.
The transistor must be a small-signal type with a rela-
tively high forward voltage; otherwise, the A/D input
voltage range can be violated. The forward voltage at
the highest expected temperature must be greater than
0.25V at 10µA, and at the lowest expected tempera-
ture, forward voltage must be less than 0.95V at 100µA.
Large power transistors must not be used. Also, ensure
that the base resistance is less than 100Ω. Tight speci-
fications for forward-current gain (50 < ß < 150, for
example) indicate that the manufacturer has good
process controls and that the devices have consistent
V
When sensing local temperature, these temperature
sensors are intended to measure the temperature of the
PC board to which they are soldered. The leads pro-
BE
characteristics.
±1°C Fail-Safe Remote/Local Temperature
Thermal Mass and Self-Heating
BE
_______________________________________________________________________________________
above ground by an internal diode
A/D Conversion Sequence
Remote-Diode Selection
Sensors with SMBus Interface
vide a good thermal path between the PC board traces
and the die. Thermal conductivity between the die and
the ambient air is poor by comparison, making air-tem-
perature measurements impractical. Because the ther-
mal mass of the PC board is far greater than that of the
MAX6680/MAX6681, the device follows temperature
changes on the PC board with little or no perceivable
delay.
When measuring the temperature of a CPU or other IC
with an on-chip sense junction, thermal mass has virtu-
ally 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 (e.g., a SOT23) 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.
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, an 8Hz conversion rate, and ALERT sinking 1mA,
the typical power dissipation is V
1mA, which equals 2.75mW; θ
package is about +120°C/W, so assuming no copper
PC board heat sinking, the resulting temperature rise is:
Even under these engineered circumstances, it is diffi-
cult to introduce significant self-heating errors.
The integrating ADC used has good noise rejection for
low-frequency signals such as 60Hz/120Hz power-sup-
Table 1. Remote-Sensor Transistor
Manufacturers
Note: Transistors must be diode connected (base shorted to
collector).
Central Semiconductor (USA)
On Semiconductor (USA)
Rohm Semiconductor (USA)
Samsung (Korea)
Siemens (Germany)
Zetex (England)
MANUFACTURER
∆T
=
2 75
.
mW
×
120
°
C W
ADC Noise Filtering
J-A
/
CC
for the 16-pin QSOP
=
FMMT3904CT-ND
2N3904, 2N3906
✕
0 330
MODEL NO.
KST3904-TF
.
CMPT3904
SMBT3904
550µA + 0.4V
SST3904
°
C
CC
7
=
✕