1 differential temperature measurement -37, 2 single-ended temperature measurement -37, 5 remote temperature sensor selection -37 – Maxim Integrated MAXQ7666 User Manual
Page 127: 5 digital-to-analog converter (dac) port -37
MAXQ7665/MAXQ7666 User’s Guide
3-37
3.4.4.1 Differential Temperature Measurement
For differential temperature measurements, connect the anode of a diode-connected transistor to the even input channel and the cath-
ode to the odd input channel of an input pair AIN0/AIN1 or AIN2/AIN3. Run the two sensor connection lines parallel to each other with
minimum spacing. This improves temperature measurement accuracy by minimizing the differential noise between the two lines, since
they have equal exposure to most sources of noise. For further improved noise rejection, shield the two sensor connections by running
them between ground planes, when available.
Configure the MAXQ7665/MAXQ7666 temperature sensor and ADC as explained in
Section 3.4.2 for differential mode (ADCDIF = 1)
and enable the remote temperature measurement on an even channel AIN0 or AIN2 (ADCMX2 and ADCMX1 = 01 or 10).
3.4.4.2 Single-Ended Temperature Measurement
For single-ended temperature measurements, connect the anode of a diode-connected transistor to the even input channel AIN0 or
AIN2 and the cathode to the ground. Choose ground connections for sensors away from high-current return paths to avoid the intro-
duction of errors caused by voltage drops in the boards/system ground, which is the main drawback for single-ended measurements.
Practical options for better accuracy are the use of a star-configured subsystem ground or a signal ground plane; to isolate the anode
sensor connection trace away from board and system noise sources; or to shield it with ground lines and ground planes (when avail-
able) to prevent accuracy degradation in the temperature measurements caused by magnetic/electric noise induction.
Configure the MAXQ7665/MAXQ7666 temperature sensor and ADC as explained in
Section 3.4.2 for single-ended mode (ADCDIF = 0)
and enable the remote temperature measurement on an even channel AIN0 or AIN2 (ADCMX2 and ADCMX1 = 01 or 10).
3.4.5 Remote Temperature Sensor Selection
Temperature-sensing accuracy depends on having a good quality, diode-connected, small-signal transistor as a sensor. Accuracy has
been experimentally verified for 2N3904-type devices. The transistor must be a small-signal type with low base resistance. See Table
3-11 for recommended devices.
Table 3-11. Remote Sensor Transistor Manufacturers
3.5 Digital-to-Analog Converter (DAC) Port
The MAXQ7665/MAXQ7666 have a true 12-bit voltage-output DAC with buffered outputs that supports a 15µs maximum settling time
at a 12-bit level. The DAC provides a gain of 1 relative to the external REFDAC reference voltage. The MAXQ7665/MAXQ7666 DAC
features include:
• 12-bit voltage-output DAC
• 8µs typical and 15µs maximum settling time
• Unity gain output buffer
• External reference
• Straight binary input
• Double-buffered data
• DAC load control from external pin or software write
MANUFACTURER
MODEL NUMBER
Central Semiconductor (CMPT)
CMPT3904
Fairchild Semiconductors (USA)
MMBT3904
ON Semiconductor (USA)
MMBT3904
Rohm Semiconductor (Japan)
SST3904
Zetex (England)
FMMT3904CT-ND
Diodes Inc.
MMBT3904
Maxim Integrated